Nutrition Exam 3

Estimating Energy Requirements: Age

The BMR declines during adulthood as lean body mass diminishes. This change in body composition occurs, in part, because some hormones that influence appetite, body weight, and metabolism become more, or less, active with age. Physical activities tend to decline as well, bringing the average reduction in energy expenditure to about 5 percent per decade. The decline in BMR that occurs when a person becomes less active reflects the loss of lean body mass and may be minimized with ongoing physical activity.

Estimating Energy Requirements: Body Composition and body size

The BMR is high in people who are tall and so have a large surface area The more a person weighs, the more energy is expended on basal metabolism.

Waist Circumference

• a good indicator of central obesity and its associated health risks. • In general, women with a waist circumference of greater than 35 inches (88 centimeters) and men with a waist circumference of greater than 40 inches (102 centimeters) have a high risk of central obesity-related health problems. • Waist circumference should be less than half of a person's height; the waist-to-height ratio is also a useful measure of disease risks.

Pyruvate

a 3-carbon compound that plays a key role in energy metabolism.

Enzymes

proteins that facilitate chemical reactions without being changed in the process; protein catalysts.

Clinically severe obesity

a BMI of 40 or greater or a BMI of 35 or greater with additional medical problems. A less preferred term used to describe the same condition is morbid obesity

Hypothalamus

a brain center that controls activities such as maintenance of water balance, regulation of body temperature, and control of appetite.

ATP (adenosine triphosphate)-

a common high-energy compound composed of a purine (adenine), a sugar (ribose), and three phosphate groups.

Coenzymes

complex organic molecules that work with enzymes to facilitate the enzymes' activity. Many coenzymes have B vitamins as part of their structures.

BMR decreases with age

5% decrease by 30, and the 5% more each decade

Pyruvate-to-Lactate (Anaerobic)

If the electron transport chain is unable to accept these hydrogens, as may occur when cells wither have insufficient mitochondria or an absence of sufficient oxygen, pyruvate can accept the hydrogens. • By accepting the hydrogens, pyruvate becomes lactate, and the coenzymes are freed to return to glycolysis to pick up more hydrogens • The rapid rate of glycolysis produces abundant pyruvate and releases hydrogen-carrying coenzymes more rapidly than the mitochondria can handle. • Making lactate from pyruvate removes two hydrogen ions, which actually diminishes acidity and improves the performance of tired muscles. • One possible fate of lactate is to be transported from the muscles to the liver since the liver can convert the lactate produced in muscles to glucose, which can then be returned to the muscles. • This process is known as the Cori cycle

Estimating Energy Requirements: Gender

In general, women have a lower BMR than men, in large part because men typically have more lean body mass.

Weight Maintenance preventing weight gain

Put simply, it takes more effort to prevent weight regain than to prevent weight gain. • Physical activity plays a key role in preventing weight gains and maintaining weight losses. • Weight maintenance may require a person to expend at least 2500 kcalories in physical activity per week. • To accomplish this, a person might exercise either moderately (such as brisk walking at 4 miles per hour) for 60 minutes a day or vigorously (such as fast bicycling at 18 miles per hour) for 30 minutes a day

Estimating Energy Requirements: Growth

The BMR is high in people who are growing including pregnant and lactating women, infants, children

Causes of Overweight and Obesity

The obvious answer is that they take in more energy from foods and beverages than they expend in physical activity and metabolic processes.

Estimating Energy Requirements: Physical activity

Using individual values for various physical activitiesis time-consuming and impractical for estimating the energy needs of a population. Instead, various activities are clustered according to the typical intensity of a day's efforts.

Acetyl CoA

a 2-carbon compound (acetate or acetic acid) to which a molecule of CoA is attached.

Lactate

a 3-carbon compound produced from pyruvate during anaerobic metabolism

Body Mass Index (BMI) definition

a measure of a person's weight relative to height; determined by dividing the weight (in kilograms) by the square of the height (in meters).

Leptin definition

a protein produced by fat cells under direction of the ob gene that decreases appetite and increases energy expenditure -acts as a hormone, primarily in the hypothalamus

TCA Cycle

a series of metabolic reactions that break down molecules of acetyl CoA to carbon dioxide and hydrogen atoms; also called the citric acid cycle or the Krebs cycleafter the biochemist who elucidated its reactions.

Successful weight-loss maintenance

achieving a weight loss of at least 5 to 10 percent of initial body weight and maintaining the loss for at least 1 year.

ketone bodies

acidic compounds produced by the liver during the incomplete breakdown of fat when carbohydrate is not available.

Adaptive Thermogenesis definition

adjustments in energy expenditure related to changes in environment such as extreme cold and to physiological events such as overfeeding, trauma, and changes in hormone status.

Obesogenic environment

all the factors surrounding a person that promote weight gain, such as increased food intake, especially of unhealthy choices, and decreased physical activity.

Waist Circumference definition

an anthropometric measurement used to assess a person's abdominal fat.

binge eating disorder

an eating disorder in which people overeat compulsively

lipoprotein lipase (LPL)

an enzyme that hydrolyzes triglycerides passing by in the bloodstream and directs their parts into the cells, where they can be metabolized or reassembled for storage.

Thermic Effect of Food (TEF) definition

an estimation of the energy required to process food (digest, absorb, transport, metabolize, and store ingested nutrients); also called the specific dynamic effect (SDE) of food or the specific dynamic activity (SDA) of food. The sum of the TEF and any increase in the metabolic rate due to overeating is known as diet-induced thermogenesis (DIT).

bomb calorimeter

an instrument that measures the heat energy released when foods are burned, thus providing an estimate of the potential energy of the foods.

CoA

coenzyme A; the coenzyme derived from the B vitamin pantothenic acid and central to energy metabolism.

Central obesity

excess fat around the trunk of the body; also called abdominal fat or upper-body fat.

Subcutaneous fat

fat stored directly under the skin

Visceral fat

fat stored within the abdominal cavity in association with the internal abdominal organs; also called intra-abdominal fat.

The classic rule states that

for each 3500 kcalories eaten in excess, a pound of body fat is stored; similarly, a pound of fat is lost for each 3500 kcalories expended beyond those consumed.

Hyperplasia

increase in the number of fat cells

Hypertrophy

increase in the size of fat cells

When body fat decreases

leptin decreases—which stimulates appetite and suppresses energy expenditure.

When body fat increases

leptin increases—which suppresses appetite.

Weight management

maintaining body weight in a healthy range by preventing gradual weight gains over time and losing weight if overweight, and by preventing weight losses and gaining weight if underweight.

Anaerobic

not requiring oxygen

Environmental influence: Accessibility

o Among the strongest influences on how much we eat are the accessibility, ease, and convenience of obtaining food. In general, the less effort needed to obtain food, the more likely food will be eaten. Think about it. Are you more likely to eat if half a leftover pizza is in your refrigerator or if you have to drive to the grocery store, buy a frozen pizza, and bake it for 45 minutes? o The message is clear. For people wanting to eat fewer empty-kcalorie or high-kcalorie foods, keep them out of sight in an inconvenient place, or better yet, don't even bring them home

Environmental influence: Package and Portion sizes

o As noted earlier, the sizes of packages in grocery stores as well as portion sizes at restaurants and at home have increased dramatically in recent decades, contributing to the increase in obesity in the United States. o Put simply, we tend to clean our plates and finish the package.

Environmental influence: Distractions

o Distractions influence food intake by initiating eating, interfering with internal controls to stop eating, and extending the duration of eating. o Some people start eating dinner when a favorite television program comes on, regardless of hunger. o Other people continue eating breakfast until they finish reading the newspaper. Such mindless eating can easily become overeating.

Strategies for successful weight maintenance

o Eat a low-kcalorie diet (usually small portions four to five times a day). o Follow a diet that is high in nutrient density and low in energy density. o Eat breakfast (curbs hunger). o Engage in physical activity regularly (at least 60 minutes of moderate activity daily). o Monitor weight frequently (at least weekly) and take prompt action with small gains. o Use productive problem-solving skills and positive self-talk. o Limit television time (less than 10 hours a week). o Consult a registered dietitian nutritionist, physician, or other support person (or group).

Environmental influence: Socializing

o People tend to eat more when socializing with others. o Pleasant conversations extend the duration of a meal, allowing a person more time to eat more, and the longer the meal, the greater the consumption. o In addition, by taking a visual cue from companions, a person might eat more when others at the table eat large portions or go to the buffet line for seconds. o One way to eat less is to pace yourself with the person who seems to be eating the least and slowest.

benefits of physical activity weight-management program include:

o Short-term increase in energy expenditure (from exercise and from a slight rise in metabolism) o Long-term increase in BMR (from an increase in lean tissue) o Improved body composition o Appetite control o Stress reduction and control of stress eating o Physical, and therefore psychological, well-being o Improved self-esteem

Environmental influence: Atmosphere

o The environment surrounding a meal or snack influences its duration. When the lighting, décor, aromas, and sounds of an environment are pleasant and comfortable, people tend to spend more time eating and thus eat more.

Environmental influence: Serving Containers

o We often use plates, utensils, and glasses as visual cues to guide our decisions on how much to eat and drink. o If you plan to eat a bowl of ice cream, it matters whether the bowl you select holds 8 ounces or 24 ounces. Large dinner plates and wide glasses create illusions and misperceptions about quantities consumed.

Environmental influence: Multiple choices

o When offered a large assortment of foods, or several flavors of the same food, people tend to eat more. o To limit intake, then, focus on a limited number of foods per meal; eating the same meal everyday tends to lower energy intake.

Risk factors for eating disorders among athletes include:

o Young age (adolescence) o Pressure to excel at a chosen sport o Focus on achieving or maintaining an "ideal" body weight or body fat percentage o Participation in sports or competitions that emphasize a lean appearance or judge performance on aesthetic appeal such as gymnastics, wrestling, figure skating, or dance o Weight-loss dieting at an early age o Unsupervised dieting

Coupled reactions

pairs of chemical reactions in which some of the energy released from the breakdown of one compound is used to create a bond in the formation of another compound.

Fad Diets

popular eating plans that promise quick weight loss. Most fad diets severely limit certain foods or overemphasize others • They espouse exaggerated or false theories of weight loss and advise consumers to follow inadequate diets. • Some fad diets are hazardous to health

Catabolism

reactions in which large molecules are broken down to smaller ones. Reactions release energy. -ex: hydrolysis

Anabolism

reactions in which small molecules are put together to build larger ones. Reactions require energy.

Aerobic

requiring oxygen

Resting metabolic rate (RMR)

similar to the basal metabolic rate (BMR), a measure of energy use for a person at rest in a comfortable setting, but with less stringent criteria for recent food intake and physical activity. Consequently, the RMR is slightly higher than the BMR. • RMR is slightly higher than the BMR because its criteria for recent food intake and physical activity are not as strict.

Basal metabolic rate (BMR)-

the rate of energy use for metabolism under specified conditions: after a 12-hour fast and restful sleep, without any physical activity or emotional excitement, and in a comfortable setting. It is usually expressed as kcalories per kilogram body weight per hour.

Environment

• With obesity rates rising and the gene pool remaining relatively unchanged, environment must also play a role in obesity. • Over the past 4 decades, the demand for physical activity has decreased as the abundance of food has increased. • Keep in mind that genetic and environmental factors are not mutually exclusive; in fact, their interactions create the epigenetics that provide a greater understanding of obesity and related diseases.

Energy balance

the energy (kcalories) consumed from foods and beverages compared with the energy expended through metabolic processes and physical activities.

Basal Metabolism definition

the energy needed to maintain life when a body is at complete digestive, physical, and emotional rest. -Largest piece of puzzle when explaining energy output at 50-65%

Satiety

the feeling of fullness and satisfaction that occurs after a meal and inhibits eating until the next meal. Satiety determines how much time passes between meals. • Whereas satiation tells us to "stop eating," satiety reminds us to "not start eating again. • Of course, people can override these signals, especially when presented with stressful situations or favorite foods.

Satiation

the feeling of satisfaction and fullness that occurs during a meal and halts eating. Satiation determines how much food is consumed during a meal. • During the course of a meal, as food enters the GI tract and hunger diminishes satiation occurs • As receptors in the stomach stretch and hormones such as cholecystokinin become active, the person begins to feel full.

Electron transport chain

the final pathway in energy metabolism that transports electrons from hydrogen to oxygen and captures the energy released in the bonds of ATP; also called the respiratory chain.

Epigenetics

the influence of environmental factors, such as diet and physical activity, on gene expression.

Appetite

the integrated response to the sight, smell, thought, or taste of food that initiates or delays eating.

Fatty acid oxidation

the metabolic breakdown of fatty acids to acetyl CoA; also called beta oxidation.

Glycolysis

the metabolic breakdown of glucose to pyruvate. Glycolysis does not require oxygen

Physiological fuel value

the number of kcalories that the body derives from a food, in contrast to the number of kcalories determined by calorimetry.

Hunger

the painful sensation caused by a lack of food that initiates food-seeking behavior. • hunger is the physiological response to a need for food triggered by nerve signals and chemical messengers originating and acting in the brain, primarily in the hypothalamus • Hunger can be influenced by the presence or absence of nutrients in the bloodstream, the size and composition of the preceding meal, customary eating patterns, climate, physical activity, hormones, and illnesses

Cori cycle

the pathway in which glucose is metabolized to lactate (by anaerobic glycolysis) in the muscle, lactate is converted back to glucose in the liver, and then glucose is returned to the muscle; named after the scientist who elucidated this pathway.

Set point

the point at which controls are set (for example, on a thermostat). The set-point theory that relates to body weight proposes that the body tends to maintain a certain weight by means of its own internal controls.

Body Weight and Body Composition

the proportions of muscle, bone, fat, and other tissue that make up a person's total body weight. • Direct measures of body composition are impossible in living human beings; instead, researchers assess body composition indirectly based on the following assumption: -Body Weight= fat + lean tissue (including water)

Metabolism

the sum total of all the chemical reactions that go on in living cells. Energy metabolism includes all the reactions by which the body obtains and expends the energy from food; the body releases energy, water, and carbon dioxide (and other waste products) when this occurs.

Heg diet

using a pregnancy hormone that speeds up metabolism as a dietary option

brite adipocytes

white fat cells with brown fat cell characteristics; also called beige adipocytes.

Be Realistic about Energy Intake Continued

• A reasonable suggestion for overweight and obese adults is to increase activity and reduce food intake enough to create a deficit of 500 to 750 kcalories per day. • In general, weight-loss diets need to provide about 1200 to 1500 kcalories per day for women and 1500 to 1800 kcalories a day for men. • Breakfast frequency is inversely associated with obesity and its associated risk factors—that is, people who frequently eat breakfast have a lower BMI, blood pressure, and blood cholesterol than those who tend to skip breakfast. • Eating breakfast, especially a protein-rich breakfast, improves satiety and diet quality—two factors that support healthy body weight.

Basal Metabolism

• About two-thirds of the energy the average person expends in a day supports the body's basal metabolism • Metabolic activities include the lungs inhaling and exhaling air, the bone marrow making new red blood cells, the heart beating 100,000 times a day, and the kidneys filtering wastes • The rate may vary from person to person and may vary for the same individual with a change in circumstance or physical condition. • The rate is slowest when a person is sleeping undisturbed, but it is usually measured in a room with a comfortable temperature when the person is awake, but lying still, after a restful sleep and an overnight (12 to 14 hour) fast.

Adaptive Thermogenesis

• Additional energy is expended when circumstances in the body are dramatically changed. • A body challenged to physical conditioning, extreme cold, overfeeding, starvation, trauma, or other types of stress must adapt; it has extra work to do and uses extra energy to build the tissues and produce the enzymes and hormones necessary to cope with the demand. • This energy is known as adaptive thermogenesis and in some circumstances (for example, in burn victims), it makes a considerable difference in the total energy expended.

Fad Diets' Appeal

• Americans spend an estimated $33 billion a year on weight-loss books and products. Even a plan that offers only minimal weight-loss success easily attracts a following. • Perhaps the greatest appeal of fad diets is that they tend to ignore dietary recommendations. Foods such as meats and milk products that need to be selected carefully to limit saturated fat can be eaten with abandon. • Dieters are also lured into fad diets by sophisticated—yet often erroneous—explanations of the metabolic consequences of eating certain foods. • If fad diets were as successful as some people claim, then consumers who tried them would lose weight, and their obesity problems would be solved. But this is not the case. Similarly, if fad diets were as worthless as others claim, then consumers would eventually stop pursuing them. • Clearly, this is not happening either. Most fad diets have enough going for them that they work for some people at least for a short time, but they fail to produce long-lasting results for most people.

Amino Acid Pathways

• Amino acids can enter the energy pathways in several ways. • Some amino acids can be converted to pyruvate, others are converted to acetyl CoA, and still others enter the TCA cycle directly as compounds other than acetyl CoA • As you might expect, amino acids that are used to make pyruvate can provide glucose, whereas those used to make acetyl CoA can provide additional energy or make body fat but cannot make glucose. • Amino acids entering the TCA cycle directly can continue in the cycle and generate energy; alternatively, they can generate glucose.

Health Risks of Overweight

• Among the health risks associated with obesity are diabetes, hypertension, cardiovascular disease, sleep apnea (abnormal ceasing of breathing during sleep), osteoarthritis, some cancers, gallbladder disease, kidney stones, respiratory problems (including Pickwickian syndrome, a breathing blockage linked with sudden death), infertility, and complications in pregnancy and surgery. • Obese people are more likely to be disabled in their later years. • Each year, these obesity-related illnesses cost our nation $147 billion

Overweight and Obesity

• An estimated 69 percent of the adults in the United States are now considered overweight or obese, as defined by a BMI of 25 to 29.9, or 30 and greater, respectively. • The prevalence of overweight is especially high among women, the poor, blacks, and Mexican Americans. • An estimated 32 percent of children and adolescents aged 2 to 19 years are either overweight or obese. • obesity has spread worldwide, affecting 1.4 billion adults and 40 million children younger than age 5.

Ghrelin

• Another protein, known as ghrelin, also acts as a hormone primarily in the hypothalamus • In contrast to leptin, ghrelin is secreted primarily by the stomach cells and promotes eating and weight gain by increasing smell sensitivity, stimulating appetite, and promoting efficient energy storage. • Ghrelin triggers the desire to eat. Blood levels of ghrelin typically rise before and fall after a meal—reflecting the hunger and satiety that precede and follow eating. • On average, ghrelin levels are high whenever the body is in negative energy balance, as occurs during low-kcalorie diets • Weight loss is more successful with exercise and after gastric bypass surgery, in part because ghrelin levels are relatively low. • Ghrelin levels decline again whenever the body is in positive energy balance, as occurs with weight gains.

TCA cycle ending

• As compounds in the TCA cycle lose a carbon to carbon dioxide, hydrogen atoms with their electrons are carried off by coenzymes made from the B vitamins niacin and riboflavin to the electron transport chain

electron transport chain continued

• As electrons are passed from carrier to carrier, hydrogen ions are pumped across the membrane to the outer compartment of the mitochondria. • The rush of hydrogen ions back into the inner compartment powers the synthesis of ATP. In this way, energy is captured in the bonds of ATP. • The ATP leaves the mitochondria and enters the cytoplasm, where it can be used for energy.

Glucose breakdown

• As glucose breaks down to pyruvate, hydrogen atoms with their electrons are released and carried to the electron transport chain by coenzymes made from the B vitamin niacin. • If needed, cells in the liver can make glucose again from pyruvate in a process similar to the reversal of glycolysis. • When the body needs energy quickly—as occurs when you run a quarter mile as fast as you can—pyruvate is converted to lactate. • The breakdown of glucose-to-pyruvate-to-lactate proceeds without oxygen which is known as anaerobic • This anaerobic pathway yields energy quickly, but it cannot be sustained for long—a couple of minutes at most. • When energy expenditure proceeds at a slower pace—as occurs when you jog around the track for an hour—pyruvate breaks down to acetyl CoA in an aerobic pathway • Aerobic pathways produce energy more slowly, but because they can be sustained for a long time, their total energy yield is greater

Eat Small Portions

• As mentioned earlier, portion sizes at markets, at restaurants, and even at home have increased dramatically over the years, contributing significantly to energy intake and weight gains. • We have come to expect large portions, and we have learned to clean our plates. Many of us pay more attention to these external cues defining how much to eat than to our internal cues of hunger and satiety. • For health's sake, we may need to learn to eat less food at each meal—one piece of chicken for dinner instead of two, a teaspoon of butter on vegetables instead of a tablespoon, and one cookie for dessert instead of six. • The goal is to eat enough food for adequate energy, abundant vitamins and minerals, and some pleasure, but not more.

Adaptation: Creating an Alternative Fuel

• As the fast continues, the body finds a way to use its fat to fuel the brain. It adapts by combining acetyl CoA fragments derived from fatty acids to produce an alternative energy source, ketone bodies • Normally produced and used only in small quantities, ketone bodies can efficiently provide fuel for brain cells. • Ketone body production rises until, after about 10 days of fasting, it is meeting much of the nervous system's energy needs. • A ketone body that contains an acid group (COOH) is called a Keto acid • Small amounts of keto acids are a normal part of the blood chemistry, but when their concentration rises, the pH of the blood drops, known as ketosis.

Drugs

• Based on new understandings of obesity's genetic basis and its classification as a chronic disease, much research effort has focused on drug treatments for obesity. • Experts reason that if obesity is a chronic disease, it should be treated as such—and the treatment of most chronic diseases includes drugs. • The challenge, then, is to develop an effective drug—or more likely, a combination of drugs—that can be used over time without adverse side effects or the potential for abuse. • Weight-loss drugs should be prescribed only to those with medical risks—not for cosmetic reasons—and in tandem with a healthy diet and activity program. • When used as part of a long-term, comprehensive weight-loss program, drugs can help with modest weight loss.

The kCalories-per-Gram Secret Revealed

• Because fat contains many carbon-hydrogen bonds that can be readily oxidized, it sends numerous coenzymes with their hydrogens and electrons to the electron transport chain, where that energy can be captured in the bonds of ATP. • This explains why fat yields more kcalories per gram than carbohydrate or protein.

Amino Acid Deamination

• Before entering the metabolic pathways, amino acids are deaminated that is, they lose their nitrogen-containing amino group • This provides the nitrogen needed to make nonessential amino acids and other nitrogen-containing compounds. • Any remaining ammonia is cleared from the body via urea synthesis in the liver and excretion in the kidneys.

Uncoupling Proteins white vs brown fat

• Brown fat is most metabolically active during exposure to cold. • Importantly, brown fat activity declines with age and with obesity; overweight and obese individuals have less brown fat activity than others. • Recent research has revealed that some white fat cells can undergo a process known as browning as they take on characteristics of brown fat, most notably the activity of uncoupled proteins; these fat cells have been named brite adipocytes • Interestingly, among the factors that trigger browning is physical activity. During exercise, muscle cells release a protein (the myokine irisin) that triggers the transformation of white fat cells into brite fat cells.

Bulimia Nervosa

• Bulimia nervosa is distinct from anorexia nervosa and is more prevalent, although the true incidence is difficult to establish because bulimia nervosa is not as physically apparent. • More men suffer from bulimia nervosa than from anorexia nervosa, but bulimia nervosa is still more common in women than in men • Diagnosis is based on such criteria as number and frequency of binge eating episodes, inappropriate compensatory behaviors to prevent weight gain (such as self-induced vomiting or misuse of laxatives), and self-evaluation unduly influenced by body shape and weight

Relative Energy Deficiency

• Central to RED-S is an energy deficiency—the athlete's diet is providing too little energy given the amount of energy expended to support health, activities of daily living, growth, and sports. • Sometimes energy deficiencies develop as the result of mismanaged athletic programs to quickly reduce body weight. • Energy deficiencies sometimes occur when athletes participate in unsupervised weight loss regimens or fail to eat enough during times of extreme exercise

Anorexia Nervosa

• Characteristics include a significantly low body weight caused by persistent restriction of energy intake; an intense fear of gaining weight or becoming fat, or persistent behaviors that interfere with weight gains; and a disturbance in self-perceived weight or shape. • Central to the diagnosis of anorexia nervosa is a distorted body image that overestimates personal body fatness. • Anorexia nervosa cannot be self-diagnosed. • Many people in our society are engaged in the pursuit of thinness, and denial runs high among people with anorexia nervosa. • Some women have all the attitudes and behaviors associated with the condition, but without the dramatic weight loss.

Fat Cell Metabolism LPL

• Consequently, even modest excesses in energy intake have a more dramatic impact on obese people than on lean people. When obese people eat less in an effort to lose weight, their LPL activity diminishes. • The activity of LPL in different regions of the body is partially influenced by gender. In women, fat cells in the breasts, hips, and thighs produce abundant LPL, storing fat in those body sites; in men, fat cells in the abdomen produce abundant LPL. • This enzyme activity explains why men tend to develop central obesity around the abdomen (apple-shaped) whereas women more readily develop lower-body fat around the hips and thighs (pear-shaped).

Breaking down Nutrients for Energy

• During digestion, the body breaks down the three energy-yielding nutrients—carbohydrates, fats, and proteins—into smaller molecules that can be absorbed: o From carbohydrates—glucose (and other monosaccharides) o From fats (triglycerides)—glycerol and fatty acids o From proteins—amino acids • Pyruvate can be used to make glucose. • Acetyl CoA cannot be used to make glucose. • Amino acids and glycerol can be converted to pyruvate and therefore can provide glucose for the body. • Fatty acids are converted to acetyl CoA and therefore cannot make glucose. Acetyl CoA can readily make fat.

Fasting—Inadequate Energy

• During fasting, carbohydrate, fat, and protein are all eventually used for energy but fuel must still be delivered to every cell. • As the fast begins, glucose from the liver's stored glycogen and fatty acids from the adipose tissue's stored fat travel to the cells. • Liver glycogen is depleted and blood glucose begins to fall. • The body must adjust its normal metabolism to survive without food. Starvation demands cells to degrade their components for fuel.

Set-Point Theory

• Researchers have confirmed that after weight losses, the body adjusts its metabolism. The decrease in the metabolic rate after weight loss is greater than would be expected based on body composition alone. • This adaptation helps to explain why it can be difficult for an overweight person to maintain weight losses. While set point answers some questions regarding the biology of energy balance, it fails to explain the many other influences contributing to the population's obesity epidemic.

Overriding Hunger and Satiety

• Eating can be triggered by signals other than hunger, even when the body does not need food. Some people experience food cravings when they are bored or anxious and may eat in response to any kind of stress, negative or positive. • Many people respond to external cues such as the time of day or the availability, sight, and taste of food • Environmental influences such as large portion sizes, favorite foods, or an abundance or variety of foods stimulate eating and increase energy intake. • Cognitive influences—such as perceptions, memories, intellect, and social interactions—can easily lead to weight gain. • Eating can also be suppressed by signals other than satiety, even when a person is hungry. • People with the eating disorder anorexia nervosa, for example, use tremendous discipline to ignore the pangs of hunger. • Some people simply cannot eat during times of stress, negative or positive.

Weight-gain strategies

• Eating energy dense foods o Energy-dense foods (the very ones eliminated from a successful weight-loss diet) hold the key to weight gain. Pick the highest-kcalorie items from each food group—that is, milk shakes instead of fat-free milk, salmon instead of snapper, avocados instead of cucumbers, a cup of grape juice instead of a small apple, and whole-wheat muffins instead of whole-wheat bread. • Regular meals daily • Large portions • Extra snacks • Juice and milk • Exercising to build muscles

Message Central—The Hypothalamus

• Eating is a complex behavior controlled by a variety of genetic, psychological, social, metabolic, and physiological factors • The hypothalamus appears to be the control center, integrating messages about energy intake, expenditure, and storage from other parts of the brain and from the mouth, GI tract, and liver.

Weight-Loss Products unsafe

• Ephedrine-containing supplements promote modest short-term weight loss (about 2 pounds a month), but with great risks. • These supplements have been implicated in numerous heart attacks and seizures, resulting in about 100 deaths. • For this reason, the FDA has banned the sale of ephedrine-containing supplements, but they are still readily available on the Internet. • These supplements have been implicated in numerous heart attacks and seizures, resulting in about 100 deaths. For this reason, the FDA has banned the sale of ephedrine-containing supplements, but they are still readily available on the Internet.

The Criterion of Health

• Even if our society were to accept fat as beautiful, obesity is still a major risk factor for several life-threatening diseases, including heart disease, type 2 diabetes, and some cancers. • For this reason, the most important criterion for determining how much a person should weigh and how much body fat a person needs is not appearance but good health and longevity. • Ideally, a person has enough fat to meet basic needs but not so much as to incur health risks.

What Excess Carbohydrate does

• Excess dietary carbohydrate can also displace fat in the fuel mix and when this occurs, carbohydrate spares both dietary fat and body fat from oxidation—an effect that may be more pronounced in overweight people than in lean people. • The net result: excess carbohydrate contributes to obesity or at least to the maintenance of an overweight body.

Fatty Acids-to-Acetyl CoA

• Fatty acids are taken apart two carbons at a time in a series of reactions known as Fatty acid oxidation • Each 2-carbon fragment splits off and combines with a molecule of CoA to make acetyl CoA. • As each 2-carbon fragment breaks off, hydrogens and their electrons are released and carried to the electron transport chain by coenzymes made from the B vitamins riboflavin and niacin.

Alcohol in the body

• Females only need to have 1 drink a day • Male can have 1 to 2 • This is because guys metabolize faster

Health Risks of Underweight

• Fewer than 2 percent of US adults are underweight • An underweight person, especially an older adult, may be unable to preserve lean tissue during the fight against a wasting disease such as cancer or a digestive disorder, especially when the disease is accompanied by malnutrition. • Without adequate nutrient and energy reserves, an underweight person will have a particularly tough battle against such medical stresses and face increased risks of mortality following surgeries • Underweight women develop menstrual irregularities and become infertile.

Ghrelin research

• Findings from an interesting research study suggest that a person's mindset also influences ghrelin's response to a meal. • These researchers suggest there may be a physiological benefit to adopting a psychological mindset of indulgence when eating low-energy-density, healthy foods. • These two proteins—leptin and ghrelin—illustrate some of the complex factors involved in the regulation of food intake and energy homeostasis.

Slow down

• For health's sake, we may need to learn to eat less food at each meal—one piece of chicken for dinner instead of two, a teaspoon of butter on vegetables instead of a tablespoon, and one cookie for dessert instead of six. The goal is to eat enough food for adequate energy, abundant vitamins and minerals, and some pleasure, but not more. • Consequently, energy intake is lower when meals are eaten slowly. Savoring each bite also activates the pleasure centers of the brain. Some research suggests that people may overeat when the brain doesn't sense enough gratification from food. Faster eating correlates with higher BMI.

Genetics and Epigenetics

• Genetics plays a true causative role in relatively few cases of obesity, for example, in Prader-Willi syndrome—a genetic disorder characterized by excessive appetite, massive obesity, short stature, and often mental retardation. • Most cases of obesity, however, do not stem from a single gene, yet multiple genetic influences do seem to be involved. • Researchers have found that adopted children tend to be more similar in weight to their biological parents than to their adoptive parents. • Studies of twins yield similar findings: compared with fraternal twins, identical twins are far more likely to weigh the same. • Clearly, something genetic makes a person more or less likely to gain or lose weight when overeating or undereating. Some people gain more weight than others on comparable energy intakes. • Researchers have been examining the human genome in search of genetic and epigenetic answers to obesity questions.

Glycerol-to-Pyruvate

• Glycerol is a 3-carbon compound like pyruvate but with a different arrangement of H and OH on the C. • As such, glycerol can easily be converted to another 3-carbon compound that can go either "up" to glucose or "down" to pyruvate and then to acetyl CoA

Emphasize Nutritional Adequacy

• Healthy diet plans make nutritional adequacy a priority. Nutritional adequacy is difficult to achieve on fewer than 1200 kcalories a day, and most healthy adults need never consume any less. • A plan that provides an adequate intake supports a healthier and more successful weight loss than a restrictive plan that creates feelings of starvation and deprivation, which can lead to an irresistible urge to binge. • Specifies the amounts of foods from each food group for diets providing 1200 to 1800 kcalories. • Such an intake would allow most people to lose weight and still meet their nutrient needs with careful, low-kcalorie, nutrient-dense food selections. • Keep in mind, too, that well-balanced diets that emphasize fruits, vegetables, whole grains, lean protein foods, and low-fat milk products offer many health rewards even when they don't result in weight loss. • A dietary supplement providing vitamins and minerals—especially iron and calcium for women—at or below 100 percent of the Daily Values can help people following low-kcalorie diets to achieve nutrient adequacy.

Body Mass Index (BMI)

• Healthy weight falls between a BMI of 18.5 and 24.9 • Underweight below 18.5 • Overweight 25 to 29.9 • Obese above 30 • More than two-thirds of adults in the United States have a BMI greater than 25

Pyruvate-to-Acetyl CoA (Aerobic)

• If a cell needs energy and oxygen is available, pyruvate molecules enter the mitochondria of the cell. • There a carbon group (COOH) from the 3-carbon pyruvate is removed to produce a 2-carbon compound that bonds with a molecule of CoA, becoming acetyl CoA. • The carbon group from pyruvate becomes carbon dioxide , which is released into the blood, circulated to the lungs, and breathed out.

Remember water

• In addition to lowering the energy density of foods, water seems to help those who are trying to lose or maintain weight. • For one, foods with high water content (such as broth-based soups) increase fullness, reduce hunger, and consequently reduce energy intake. • For another, drinking a large glass of water before a meal eases hunger, fills the stomach, and consequently reduces energy intake. • Importantly, water adds no kcalories. • The average US diet delivers an estimated 75 to 150 kcalories a day from sweetened beverages. Simply replacing nutrient-poor, energy-dense beverages with water can help a person achieve a 5 percent weight loss at 6 months.

Adaptation: Conserving Energy

• In an effort to conserve body tissues for as long as possible, the hormones of fasting slow metabolism. • As the body shifts to the use of ketone bodies, it simultaneously reduces its energy output and conserves both its fat and its lean tissue.

The Criterion of Fashion

• In asking what is ideal, people often mistakenly turn to friends and fashion for the answer and judge body weight by appearances. • No doubt our society sets unrealistic ideals for body weight, especially for women. • Magazines, movies, and television all convey the message that to be thin is to be beautiful and happy. • As a result, the media have a great influence on the weight concerns and dieting patterns of people of all ages, but most tragically on young, impressionable children and adolescents.

Uncoupling Proteins

• In brown adipose tissue, oxidation is uncoupled from ATP formation, producing heat only. • By radiating energy away as heat, the body expends, rather than stores, energy. In contrast, efficient coupling facilitates synthesis reactions, including the making of fat for storage. • Brown fat and heat production is particularly important in newborns and in animals exposed to cold weather, especially those that hibernate. • In contrast, human adults have little brown fat, stored primarily around the neck and clavicles.

Estimating Energy Requirements

• In estimating energy requirements, the DRI Committee developed equations based on research measuring total daily energy expenditure.

Basal Metabolism Continued

• In general, the more a person weighs, the more total energy is expended on basal metabolism, but the amount of energy per pound of body weight may be lower. o For example, an adult's BMR might be 1500 kcalories per day and an infant's only 500, but compared to body weight, the infant's BMR is more than twice as fast.

Physical inactivity

• Life requires little exertion—escalators carry us up stairs, automobiles take us across town, and remote controls change television channels from a distance. Modern technology has replaced physical activity at home, at work, and in transportation. • Inactivity contributes to weight gain and poor health. Most physical inactivity occurs when watching television, playing video games, and using the computer. • Sedentary activities contribute to weight gain in several ways. First, they require little energy beyond the resting metabolic rate. Second, they replace time spent in more vigorous activities. Third, watching television influences food purchases and correlates with between-meal snacking on the high-kcalorie, solid fat and added sugars foods and beverages most heavily advertised.

Bulimia Nervosa Characteristics

• Like the person with anorexia nervosa, the person with bulimia nervosa spends much time thinking about body image and food • The preoccupation with food manifests itself in secret binge-eating episodes, which usually progress through several emotional stages: anticipation and planning, anxiety, urgency to begin, rapid and uncontrollable consumption of food, relief and relaxation, disappointment, and finally shame or disgust. • A bulimic binge is characterized by a sense of no control over eating.

Bulimia Nervosa Treatment

• Major steps toward recovery include discontinuing purging and restrictive dieting habits and learning to eat three meals a day plus snacks. • A mental health professional should be on the treatment team to help clients with their depression and addictive behaviors. • Most women diagnosed with bulimia nervosa recover within 5 to 10 years, with or without treatment, but treatment probably speeds the recovery process.

The Helpers in Metabolic Reactions—Enzymes and Coenzymes

• Metabolic reactions almost always require enzymes to facilitate their action. • In many cases, the enzymes need assistants to help them from assistors known as coenzymes • Coenzymes work closely with enzymes but are not proteins themselves • The relationships between various coenzymes and their respective enzymes may differ in detail, but one thing is true of all: without its coenzyme, an enzyme cannot function

Weight-Loss Products

• Millions of people in the United States use over-the-counter weight-loss products. • Most users are women, especially young overweight women, but almost 10 percent are of normal weight. • In their search for weight-loss magic, some consumers turn to "natural" herbal products and dietary supplements, even though few have proved to be effective and many have proved to be harmful. • For example, in addition to the many cautions that accompany the use of all herbal remedies, consumers should be aware that St. John's wort is often prepared in combination with the herbal stimulant ephedrine. •

Lower Energy Density

• Most people take their cues about how much to eat based on portion sizes, and the larger the portion size, the more they eat. To lower energy intake, a person can either reduce the portion size or reduce the energy density. • educing energy density while maintaining or even increasing food quantity, especially by reducing fat and including fruits and vegetables, seems to be a successful strategy to control hunger and manage weight. • Because a low-energy-density diet is a low-fat, high-fiber diet rich in many vitamins and minerals, it supports good health in addition to weight loss.

Adaptation: Making Glucose

• Normally, the brain and nerve cells consume about half of the total glucose used each day (about 500 kcalories' worth). • About one-fourth of the energy the adult body uses when it is at rest is spent by the brain. • During a fast, the need for glucose poses a major problem. • The body can use its stores of fat, which may be quite generous, to furnish most of its cells with energy, but the red blood cells are completely dependent on glucose, and the brain and nerves prefer energy in the form of glucose. • Amino acids that yield pyruvate can be used for gluconeogenesis or the making of glucose from a noncarbohydrate source • The liver is the major site of gluconeogenesis, but the kidneys become increasingly involved under certain circumstances, such as starvation. • The glycerol portion of a triglyceride and most amino acids can be used to make glucose

Overeating

• One explanation for obesity is that overweight people overeat, although diet histories may not always reflect high intakes. • Diet histories are not always accurate records of actual intakes; both normal-weight and obese people commonly misreport their dietary intakes. • Obese people who had a positive energy balance for years and accumulated excess body fat may not currently have a positive energy balance. • Both present and past eating and activity patterns influence current body weight. • We live in an environment that exposes us to an abundance of high-kcalorie, high-fat foods that are readily available, relatively inexpensive, heavily advertised, and reasonably tasty. • Most alarming are the extraordinarily large portions and ready-to-go combo-meals. Eating large portion sizes multiple times a day accounts for much of the weight increase seen over the decades.

Disordered Eating

• One reason many athletes engage in disordered eating is that they and their coaches have embraced unsuitable weight standards. An athlete's body must be heavier for a given height than a nonathlete's body because the athlete's body is dense, containing more healthy bone and muscle and less fat. • Disordered eating among athletes usually involves energy deficits and weight loss, but some athletes, usually males, go to extreme measures to bulk up and gain weight.

Choose fats sensibly

• One way to lower energy intake is to lower fat intake. Lowering the fat content of a food lowers its energy density—for example, selecting fat-free milk instead of whole milk. That way, a person can consume the usual amount (say, a cup of milk) at a lower energy intake (85 instead of 150 kcalories). • Fat has a weak satiating effect, and satiation plays a key role in determining food intake during a meal. Consequently, a person eating a high-fat meal increases energy intake in two ways—more food and more fat kcalories. For these reasons, measure fat with extra caution.

Other Gimmicks

• Other gimmicks don't help with weight loss either. • Hot baths do not speed up metabolism so that pounds can be lost in hours. • Steam and sauna baths do not melt the fat off the body, although they may dehydrate people so that they lose water weight. • Brushes, sponges, wraps, creams, and massages intended to move, burn, or break up fat do nothing of the kind.

Prevention

• Over the years, these strategies become an integral part of a person's life: o Eat regular meals and limit snacking o Drink water instead of high-kcalorie beverages o Select sensible portion sizes and limit daily energy intake to no more than energy expended o Become physically active and limit sedentary activities

Oxaloacetate in TCA Cycle

• Oxaloacetate's role in replenishing the TCA cycle is critical because when oxaloacetate is insufficient, the TCA cycle slows down, and the cells face an energy crisis. • Oxaloacetate is made primarily from pyruvate, although it can also be made from certain amino acids, however oxaloacetate cannot be made from fat. • Oxaloacetate must be available for acetyl CoA to enter the TCA cycle which underscores the importance of carbohydrates in the diet. A diet that provides ample carbohydrate ensures an adequate supply of oxaloacetate—because glucose produces pyruvate during glycolysis. • Oxaloacetate is the first 4-carbon compound to enter the TCA cycle and then picks up acetyl CoA drops off one carbon (as carbon dioxide), then another carbon (as carbon dioxide), and returns to pick up another acetyl CoA.

Sustaining Satiation and Satiety

• Protein is considered most satiating out of the three energy yielding nutrients • Too little protein in the diet can leave a person feeling hungry. • Including some protein—such as drinking milk—provides satiety and decreases energy intake at the next meal. • Fructose in a sugary fruit drink seems to stimulate appetite and increase food intake. • The best nutrient as causing a satiating affect is complex carbohydrates • Fat has a weak satiating effect

ATP conversion

• Quite often, the hydrolysis of ATP occurs simultaneously with reactions that will use that energy a metabolic duet known as coupled reactions • In essence, the body uses ATP to transfer the energy released during catabolic reactions to power anabolic reactions that require energy. • The body converts the chemical energy of food to the chemical energy of ATP with about 50 percent efficiency, radiating the rest as heat. • Some energy is lost as heat again when the body uses the chemical energy of ATP to do its work o EX: moving muscles, synthesizing compounds, or transporting nutrients, for example.

Leptin

• Researchers have identified an obesity gene, called ob, that is expressed primarily in the adipose tissue and codes for the protein leptin • Leptin maintains homeostasis by regulating food intake and energy expenditure in response to adipose tissue. • Although extremely rare, a genetic deficiency of leptin or genetic mutation of its receptor has been identified in human beings as well. Extremely obese children with barely detectable blood levels of leptin have little appetite control; they are constantly hungry and eat considerably more than their siblings or peers. • Very few obese people have a leptin deficiency, however. • In fact, leptin levels increase as BMI increases. Leptin rises but fails to suppress appetite or enhance energy expenditure—a condition researchers describe

Other Measures of Body Composition

• Researchers sometimes estimate body composition using these methods: total body water, radioactive potassium count, near-infrared spectrophotometry, ultrasound, computed tomography, and magnetic resonance imaging.

Weight Maintenance

• Some look at success after 1 year and others after 5 years; some quantify success as 10 or more pounds lost and others as 5 or 10 percent of initial body weight lost. • An estimated one out of every six overweight adults in the United States has successfully maintained at least a 10 percent loss for at least a year. • Those who are successful in maintaining their weight loss have established regular exercise regimens and careful eating patterns, taking in less energy than the national average. • Because formerly overweight people are more efficient at storing fat, they do not have the same flexibility in their food and activity habits as their friends who have never been overweight.

The Transfer of Energy in Reactions—ATP

• Some of the energy released during the breakdown of glucose, glycerol, fatty acids, and amino acids is captured in the high-energy compound ATP • The negative charges on the phosphate groups make ATP vulnerable to hydrolysis. • When the bonds between the phosphate groups are hydrolyzed, they readily break, splitting off one or two phosphate groups and releasing energy. In this way, ATP provides the energy that powers all the activities of living cells.

Dangerous Interventions

• Some people attach so many dreams of happiness to weight loss that they willingly risk huge sums of money for the slightest chance of success. As a result, weight-loss schemes flourish. • The negative consequences must be carefully considered before embarking on any weight-loss program. • Some of the nation's most popular diet books and weight-loss programs have misled consumers with unsubstantiated claims and deceptive testimonials • Some weight-loss programs are better than others in terms of cost, approach, and customer satisfaction

Changes, Losses, and Goals

• Successful weight-loss strategies embrace changes, celebrate losses, and set goals. • A comprehensive lifestyle approach that includes low-kcalorie, nutrient-dense foods and regular physical activity supports both weight loss and health benefits. • Even modest weight loss brings health benefits. Modest weight loss, even when a person is still overweight, can improve blood glucose and reduce the risks of heart disease by lowering blood pressure and blood cholesterol, especially for those with central obesity. • Improvements in physical capabilities and quality of life become evident with even a 5 percent weight loss • Depending on initial body weight, a reasonable rate of loss for overweight adults is 1/2 to 2 pounds a week, or 5 to 10 percent of body weight over 6 months. For a person weighing 250 pounds, a 10 percent loss is 25 pounds, or about 1 pound a week for 6 months.

surgery may be an option

• Surgery may be an option for people with all of the following conditions: o Unable to achieve adequate weight loss with diet and exercise o BMI more than 40 or BMI greater than 35 with weight-related health problems (such as diabetes or hypertension) o No medical or psychological contraindications o Understanding of risks and strong motivation to comply with post-surgery treatment plan

BMR is high or increased when

• The BMR is highest in people who are growing (children, adolescents, and pregnant women) and in those with considerable lean body mass (physically fit people and males). • One way to increase the BMR, then, is to participate in endurance and strength-training activities regularly to maximize lean body mass. • The BMR is also high in people with fever or under stress and in people with highly active thyroid glands. • The BMR slows down with a loss of lean body mass and during fasting and malnutrition.

TCA Cycle described

• The TCA cycle is the final common metabolic pathway for carbohydrates, fats, and amino acids. • This reactions take place in the inner compartment of the mitochondria. • When cells need energy, acetyl CoA enters the TCA cycle, a busy metabolic traffic center. • The TCA cycle is a circular path, but that doesn't mean it regenerates acetyl CoA. • Acetyl CoA goes one way only—down to two carbon dioxide molecules and a coenzyme (CoA). • The TCA cycle is a circular path because a 4-carbon compound known as oxaloacetate is needed in the first step and it is synthesized in the last step.

Surgery

• The US prevalence of clinically severe obesity is estimated at 6 percent. • At this level of obesity, lifestyle changes and modest weight losses can improve disease risks a little, but the most effective treatment is surgery. • More than 100,000 such surgeries are performed in the United States annually • In addition, gastric bypass suppresses hunger by changing production of gastrointestinal hormones. • Because the long-term safety and effectiveness of surgery depend, in large part, on compliance with dietary instructions, nutrition care plays an important role in follow-up treatment. • Vitamin and mineral deficiencies are common, and dietary supplements are routinely prescribed • Another surgical procedure removes some fat deposits by liposuction. This cosmetic procedure has little effect on body weight (less than 10 pounds), but can alter body shape slightly in specific areas. • Liposuction is a popular procedure in part because of its perceived safety, but immediate and delayed complications can arise

physical activity

• Whether trying to minimize weight gains or support weight losses, the best approach includes physical activity. • To prevent weight gains and support weight losses, current recommendations advise 200 to 300 minutes of moderately intense physical activity a week in addition to activities of daily life. • People who combine diet and exercise typically lose more fat, retain more muscle, and regain less weight than those who only follow a weight-loss diet. • Even when they do not lose more weight, they seem to follow their diet plans more closely and maintain their losses better than those who do not exercise.

Food Composition

• The amount of heat given off provides a direct measure of the food's energy value • In addition to releasing heat, these reactions generate carbon dioxide and water—just as the body's cells do when they metabolize the energy-yielding nutrients from foods. • A bomb calorimeter measures the available energy in foods but overstates the physiological fuel value • The body is less efficient than a calorimeter and cannot metabolize all of the energy-yielding nutrients in a food completely. • The body is less efficient than a calorimeter and cannot metabolize all of the energy-yielding nutrients in a food completely. • These values provide reasonable estimates, but they do not reflect the precise amount of energy a person will derive from the foods consumed.

Excess Carbohydrate

• The body handles abundant carbohydrate by first storing it as glycogen, but glycogen storage areas are limited and fill quickly. • Because maintaining glucose balance is critical, the body uses glucose frugally when the diet provides only small amounts and freely when supplies are abundant. • In other words, glucose oxidation rapidly adjusts to the dietary intake of carbohydrate. • Like protein, excess glucose can also be converted to fat directly however this pathway is relatively minor. • As mentioned earlier, converting glucose to fat is energetically expensive and does not occur until after glycogen stores have been filled but, new body fat is made whenever carbohydrate intake is excessive.

Uncoupling Proteins 2 types

• The body has two main types of fat: white and brown adipose tissue. White adipose tissue stores fat for other cells to use for energy; brown adipose tissue releases stored energy as heat, thus defending against cold and preventing obesity.

Adaptation: Making Glucose effect on body

• The breakdown of body protein is an expensive way to obtain glucose. In the first few days of a fast, body protein provides about 90 percent of the needed glucose; glycerol, about 10 percent. • If body protein losses were to continue at this rate, death would follow within three weeks, regardless of the quantity of fat a person had stored.

electron transport chain

• The electron transport chain captures energy in the high-energy bonds of ATP and consists of a series of proteins that serve as electron "carriers." • These carriers are mounted in sequence on the inner membrane of the mitochondria • As the coenzymes deliver their electrons from the TCA cycle, glycolysis, and fatty acid oxidation to the electron transport chain, each carrier receives the electrons and passes them on to the next carrier. • These electron carriers continue passing the electrons down until they reach oxygen. Oxygen (O) accepts the electrons and combines with hydrogen atoms (H) to form water

Fat Cell Metabolism

• The enzyme lipoprotein lipase plays a major role in the metabolism and transport of lipids, and consequently is a participant in the development of obesity. • One of its roles is to remove triglycerides from the blood for storage in both adipose tissue and muscle cells. • Obese people generally have much more LPL activity in their adipose cells than lean people do • This high LPL activity makes fat storage especially efficient.

Glucose

• The first pathway glucose takes on its way to yield energy is called glycolysis • In a series of reactions, the 6-carbon glucose is converted to similar 6-carbon compounds before being split in half, forming two 3-carbon compounds. These 3-carbon compounds continue along the pathway until they are converted to pyruvate. • Thus the net yield of one glucose molecule is two pyruvate molecules • The net yield of energy at this point is small; to start glycolysis, the cell needs a little energy and then releases only a little more than it invested initially.

The Site of Metabolic Reactions—Cells

• The human body is made up of trillions of cells, and each cell busily conducts its metabolic work all the time. • The type and extent of metabolic activities vary depending on the type of cell, but of all the body's cells, the liver cells are the most versatile and metabolically active.

Fat Distribution

• The location of fat on the body may influence health as much, or more than, total fat alone • Visceral fat that is stored around the organs of the abdomen is referred to as central obesity or upper-body fat • Central obesity contributes to heart disease, cancers, diabetes, and related deaths • Visceral fat is most common in men and to a lesser extent in women past menopause. • Even when total body fat is similar, men have more visceral fat than women. • Subcutaneous fat around the hips and thighs, sometimes referred to as lower-body fat, is most common in women during their reproductive years, and is associated with lower heart disease risks

Be Realistic about Energy Intake

• The main characteristic of a weight-loss diet is that it provides less energy than the person needs to maintain present body weight. If food energy is restricted too severely, dieters may not receive sufficient nutrients. • Rapid weight loss usually means excessive loss of lean tissue, a lower BMR, and rapid weight regains to follow. • The composition of regained weight is more fat and less lean than the composition of the originally lost weight. • Energy intake should provide nutritional adequacy without excess—that is, somewhere between deprivation and complete freedom to eat whatever, whenever.

Fat Cell Metabolism in weight loss

• The release of lower-body fat is less active in women than in men, whereas the release of upper-body fat is similar. • The rate of fat breakdown is lower in women than in men. • Women may have a more difficult time losing fat in general, and from the hips and thighs in particular. • Enzyme activity may also explain why some people who lose weight regain it so easily. After weight loss and weight stabilization, adipose tissue LPL is increased and its response to meals is heightened. • It's as if the LPL enzyme gene is saying "Make more fat-storing enzymes." • People easily regain weight after having lost it because they are battling against enzymes that want to store fat. Fat storage is efficient, and fat oxidation is not.

Physical Activity

• The second component of a person's energy output is physical activity at 30 to 50%. • Physical activity is the most variable—and the most changeable—component of energy expenditure meaning its influence on both weight gain and weight loss can be significant. • During physical activity, the muscles need extra energy to move, and the heart and lungs need extra energy to deliver nutrients and oxygen and dispose of wastes.

Anorexia Nervosa consequences

• The starvation of anorexia nervosa damages the body just as the starvation of war and poverty does. • In fact, most people with anorexia nervosa are malnourished. • Their bodies have been depleted of both body fat and protein. • They lose so much lean tissue that their basal metabolic rate slows. • In addition, the heart pumps inefficiently and irregularly, the heart muscle becomes weak and thin, the chambers diminish in size, and the blood pressure falls. • Minerals that help to regulate heartbeat become unbalanced. • Many deaths occur because of multiple organ system failure when the heart, kidneys, and liver cease to function. • Starvation brings other physical consequences as well, such as loss of brain tissue, impaired immune response, anemia, and a loss of digestive functions that worsen malnutrition.

Food intake

• To achieve energy balance, the body must meet its needs without taking in too much or too little energy

Anorexia Nervosa Treatment

• Treatment of eating disorders requires a multidisciplinary approach.Teams of physicians, nurses, psychiatrists, family therapists, and dietitians work together to resolve two sets of issues and behaviors: those relating to food and weight and those involving relationships with oneself and others. o The first dietary objective is to stop weight loss while establishing regular eating patterns.

Excess Fat

• Unlike excess protein and carbohydrate, which both increase oxidation, eating too much fat does not promote fat oxidation. • Instead, excess dietary fat moves efficiently into the body's fat stores; almost all of the excess is stored.

Overweight in Good Health

• Weight loss is recommended for people who are obese and those who are overweight with one or more of the following risk factors for chronic diseases: o Hypertension o Cigarette smoking o Abnormal blood lipids o Diabetes or prediabetes o Family history of heart disease o Men 45 or older and women 55 or older • A 50-year-old man with a BMI of 28 who has high blood pressure and a family history of heart disease can improve his health by adjusting his diet and engaging in a regular exercise plan.

Fat Cell Development

• When "energy in" exceeds "energy out," much of the excess energy is stored in the fat cells of adipose tissue. The amount of fat in adipose tissue reflects both the number and the size of the fat cells. • he number of fat cells increases most rapidly during the growing years of late childhood and early puberty. • After growth ceases, fat cell numbers may continue to increase whenever energy balance is positive. • Obese people have more fat cells than healthy-weight people; their fat cells are also larger. • As fat cells accumulate triglycerides, they expand in size • When the cells enlarge, they stimulate cell proliferation so that their numbers increase again.

Low-Carbohydrate Diets

• When a person consumes a low-carbohydrate diet, a metabolism similar to that of fasting prevails. • With little dietary carbohydrate coming in, the body uses its glycogen stores to provide glucose for the cells of the brain, nerves, and blood. • Once the body depletes its glycogen reserves, it begins making glucose from the amino acids of protein

Feasting—Excess Energy

• When a person eats too much, metabolism favors fat formation. Fat cells enlarge regardless of whether the excess in kcalories derives from protein, carbohydrate, or fat. • The pathway from dietary fat to body fat, however, is the most direct (and the most efficient. • To convert a dietary triglyceride to a triglyceride in adipose tissue, the body removes two of the fatty acids from the glycerol, absorbs the parts, and puts them together again. • The body uses much less energy to convert dietary fat to body fat than it does to convert dietary carbohydrate to body fat • On average, storing excess energy from dietary fat as body fat uses only 5 percent of the ingested energy intake, but storing excess energy from dietary carbohydrate as body fat requires 25 percent of the ingested energy intake.

Thermic Effect of Food (TEF)

• When a person eats, the GI tract muscles speed up their rhythmic contractions, the cells that manufacture and secrete digestive juices become active, and some nutrients require energy to be absorbed. • This acceleration of activity requires energy and produces heat; it is known as the thermic effect of food (TEF) • *The thermic effect of food is proportional to the food energy taken in and is usually estimated at 10 percent of energy intake.* o Thus a person who ingests 2000 kcalories probably expends about 200 kcalories on the thermic effect of food. • The proportions vary for different foods, however, and are also influenced by factors such as meal size and frequency. • In general, the thermic effect of food is greater for high-protein foods than for high-fat foodsand for a meal eaten all at once rather than spread out over a couple of hours.

Excess Protein

• When a person overeats protein, the body uses the surplus first by replacing normal daily losses and then by increasing protein oxidation. • An increase in protein oxidation uses some excess protein, but it displaces fat in the fuel mix. • If excess protein is still available, the amino acids are deaminated and the remaining carbons are used to make fatty acids, which are stored as triglycerides in adipose tissue.

Fatty Acids Cannot Make Glucose

• When carbohydrate is unavailable, liver cells can make glucose from pyruvate and other 3-carbon compounds, such as glycerol. • Cells cannot make glucose from the 2-carbon fragments of fatty acids.

Breaking down Nutrients for Energy Continued

• Whereas most of the body's cells can use glucose, fat, or both for energy, the body must have glucose to fuel the activities of the central nervous system and red blood cells. • Without glucose from food, the body will break down its own lean (protein-containing) tissue to get the amino acids needed to make glucose. To protect this protein tissue, the body needs foods that provide glucose—primarily carbohydrate. • Eating only fat provides abundant acetyl CoA, but forces the body to break down protein tissue to make glucose. • Eating only protein requires the body to convert protein to glucose. • Clearly, the best diet provides ample carbohydrate (45 to 65 percent of kcalories), adequate protein (10 to 35 percent of kcalories), and some fat (20 to 35 percent of kcalories). • Acetyl CoA enters the TCA Cycle and the energy is harness through the electron transport chain