Chapter 18 Nutrition and Metabolism

cholesterol

abundant in liver and egg yolk and whole milk, butter, cheese, and meats foods of plant origin do not contain cholesterol

nutrition

adequate nutrients

lacto vegetarian

dairy allowed; no eggs or meat

lacto ovo vegetarian

dairy and eggs allowed; no meat

ovo vegetarian

eggs allowed; no dairy or meat

lip

fat: lipids--fat or fatlike substance insoluble in water

Protein sources

foods rich in proteins include meats, fish, poultry, cheese, nts, milk, eggs, and cereals legumes, including beans and peas, contain less protein the body can synthesize many amino acids (nonessential amino acids). eight amino acids the adult body needs (ten required for growing children) can not be synthesized sufficiently or at all, and they are called essential amino acids. this term refers only to dietary intake, because all amino acids are required for normal protein synthesis.

Lipid Uses

glycerol and fatty acid molecules resulting from the hydrolysis of fats can also combine to form fat molecules in anabolic reactions and be stored in fat tissue. additional fat molecules can be synthesized from excess glucose or amino acids. the liver can convert fatty aids from one form to another the liver cannot synthesize certain fatty acids called essential fatty acids. linoleic acid is an essential fatty acid required to synthesize phospholipids which are necessary for constructing cell membranes and myelin sheaths and for transporting circulating lipids. linoleic acid: corn oil, cottonseed oil, soy oil linolenic acid is an essential fatty acid

calor

heat: calorie--unit used to measure heat or energy content of foods

neuropeptide Y

hypothalamus enances appetite

lipid use

in foods are phospholipids, cholesterol, fats (triglycerides) fats mainly supply energy. gram for gram fats contain more than twice as much chemical energy as carbohydrates or proteins before a triglyceride molecule can release energy, it must undergo hydrolysis. this happens when digestion breaks triglycerides down into fatty acids and glycerol. after being absorbed, these products are transported in the lymph to the blood, then on to tissues fatty acid portions can form molecules of acetyl coenzyme A (acetyl CoA) by a series of reactions called beta oxidation, which occurs in the mitochondria.

Appetite control

interacting hormones control by affecting part of the hypothalamus called the arcuate nucleus

Two major classes of nutrients

macronutrients: needed in bulk, are carbohydrates, lipids, and proteins. micronutrients: essential in small daily doses and include vitamins and minerals.

meter

measure: calorimeter--instrument used to measure the caloric content of food

carbohydrate use

monosaccharides absorbed from the digestive tract include fructose, galactose, and glucose. liver enzymes catalyze reactions that convert fructose and galactose into glucose excess glucose is polymerized to form glycogen (glycogenesis), which the liver and muscles store as a glucose reserve the body requires a minimum amount if the body does not have an adequate supply, the liver may convert some noncarbohydrates, such as amino acids from proteins or glycerol from fats, into glucose--a process called gluconeogenesis. cells use carbohydrates as starting materials for synthesizing such vital biochemicals as the 5 carbon sugars ribose and deoxyribose, sugars required for the production of the nucleic acids RNA and DNA

vegan

no animal foods

nutri

nourish: nutrient--substance needed to nourish cells

carbohydrates

organic compounds include the sugars and starches the energy held in their chemical bonds is used to power cellular processes ingested in a variety of forms polysaccharides (many sugars); starch from plant foods and glycogen from meats simple carboh include disaccharides (double sugars) fro milk sugar, cane sugar monosaccharides (single sugars); honey and fruits small enough to be absorbed into the bloodstream.

carbohydrate requirements

provide the primary source of fuel for cellular processes need 125 - 15 grams daily to avoid protein breakdown and to avoid metabolic disorders resulting from excess fat use. average diet includes 200 - 300 grams of carbohydrates daily

Leptin

stimulates metabolic rate low leptin: indicate depleted fat stores; a condition in which metabolism slows to conserve energy and appetite increases

Ghrelin

stomach enhances appetite

lipid sources

triglycerides are found in plant and animal based foods saturated fats are mainly found in foods of animal origin(meat, eggs, milk, lard, palm oil, coconut oil)--in excess are risk factor for cardiovascular disease unsaturated fats (seeds, nuts, plant oils) monounsaturated fats ( olive oil, peanut oil, canola oils) are healthiest

pell

skin: pellagra--vitamin deficiency condition characterized by inflammation of the skin and other symptoms

Appetite

the drive that compels us to seek food

Vitamin D

a group of steroids that have similar properties found in foods (milk, egg yolk, fish liver oils) synthesized fro dietary cholesterol that has been metabolized to provitamin D by intestinal enzymes, then stored in the skin and exposed to ultraviolet light. resists heat, oxidation, acids, and bases primarily stored in the liver and is less abundant in the skin, brain, spleen, and bones is stored in the form of hydroxycholecalciferol and is released as needed into the blood when parathyroid hormone is present, this form of vitamin D is converted in the kidneys into an active form of the vitamin (dihydroxycholecalciferol) this substance is carried as a hormone in the blood to the intestines where it stimulates production of calcium binding protein it promotes absorption of calcium and phosphorus, ensuring that adequate amounts of these minerals are available in the blood for tooth and bone formation and metabolic processes

nitrogen balance

a healthy adult continuously builds up and breaks down proteins this happens at different rates in different tissues, but the overall gain of body proteins equals the loss, producing a state of dynamic equilibrium. because proteins have a high percentage of nitrogen, dynamic equilibrium also brings nitrogen balance in which the amount of nitrogen taken in equals the amount excreted. a person who is starving has a negative nitrogen balance because the amount of nitrogen excreted as a result of amino acid oxidation exceeds the amount the diet replaces. a growing child, a pregnant woman, or an athlete in training is likely to have a positive nitrogen balance because more protein is being built into new tissue and less is being used for energy or excreted.

ghrelin

a hormone that the stomach secretes enhances appetite by stimulating the release of neuropeptide Y fasting and low calorie diet stimulate ghrelin production

Energy balance

a state of energy balance exists when caloric intake in the form of foods equals caloric expenditure from the basal metabolic rate and muscular activities. under these conditions body weight remains constant, except perhaps for slight variations due to changes in water content if caloric intake exceeds expenditure, a positive energy balance occurs, and tissues store excess nutrients this increases body weight because 3,500 excess calories is stored as a pound of fat if caloric expenditure exceeds input, the energy balance is negative, and stored materials are mobilized from the tissues for oxidation, causing weight loss

Eating stimulates adipocytes to secrete leptin which

acts on target cells in the hypothalamus the effect suppresses appetite by inhibiting release of the hypothalamic neurotransmitter neuropeptide Y that stimulates eating

leptin

adipocytes suppresses appetite and increases metabolic reate after eating

protein sources

all 20 types of amino acids must be in the body at the same time for growth and tissue repair to occur. if the diet lacks one essential amino acid, the cells cannot synthesize protein essential amino acids are not stored those not used to make proteins are oxidized as energy sources or are converted into carbohydrates or fats. proteins are classified as complete or incomplete based on the amino acid types they provide. complete proteins have adequate amounts of the essential amino acids to maintain body tissues and promote normal growth and development. certain proteins in milk, met, and eggs are complete incomplete proteins cannot by themselves maintain tissues or support normal growth and development zein in corn has too little of the essential amino acids tryptophan and lysine to be complete a partially complete protein does not have enough amino acid variety to promote growth, but it has enough to maintain life. a protein in wheat called gliadin is a partially complete protein because it has very little of the amino acid lysine.

Proteins

are polymers of amino acids they have a wide variety of functions when dietary proteins are digested, the resulting amino acids are absorbed and transported by the blood to cells. many of these amino acids are used to form new protein molecules, as specified by DNA base sequences. these new proteins include enzymes that control the rates of metabolic reactions; clotting factors; the keratins of skin and hair; elastin and collagen of connective tissue; plasma proteins that regulate water balance; the muscle components actin and myosin;; certain hormones; and the antibodies that protect against infection protein molecules may also supply energy. to do this, they must first be broken down into amino acids. the amino acids then undergo deamination, a process in the liver that removes the nitrogen containing (-NH2) groups, which then react to form a waste called urea the blood carries urea to the kidneys, where it is excreted in urine

mal

bad, abnormal: malnutrition--poor nutrition resulting from lack of food or failure to adequately use available foods

bas

base: basal metabolic rate--metabolic rate of body under resting (basal) conditions

desirable weight

body mass index (BMI) is used to assess weight considering height overweight = 10% to 20% or a BMI between 25-30 obese = over 20% with BMI over 30 (excess adipose tissue)

catabolism

breaking down

anabolism

building up or snythesis

glycogen

can be rapidly broken down to yield glucose (glycogenolysis) when it is required to supply energy. excess glucose beyond what is stored as glycogen usually reacts to form fat and is stored in adipose tissue

Energy Expenditures

carbohydrates, fats, and proteins supply energy, which is required for all metabolic processes and therefore important to cell survival. if the diet is deficient in energy supplying nutrients, structural molecules may gradually be consumed, leading to death excess intake of energy supplying nutrients may lead to obesity

carot

carrot: carotene--yellowish plant pigment that imparts the color of carrots and other yellowish plant tissue

nutrients

chemicals supplied from the environment that an organism requires for survival

cellulose

complex carbohydrate abundant in our food provides the crunch to celery and the crispness to lettuce. cannot digest cellulose provides bulk (fiber/roughage) facilitating the movement of intestinal contents. hemicellulose, pectin, and lignin are other plant carbohydrates that proved fiber.

pesco veetarian

dairy, eggs, and fish allowed; no other meat

semivegetarian

dairy, eggs, chicken, and fish allowed; no other meat

Fat soluble Vitamins

dissolve in fats they associate with lipids and are influenced by the same factors that affect lipid absorption. bile salts in the intestine promote absorption of fat soluble vitamins. as a group, the fat soluble vitamins are stored in moderate quantities in various tissue, which is why excess intake can lead to overdose. fat soluble vitamins resist the effects of heat, so cooking and food processing do not usually destroy them

Vitamin A

exists in several forms, including retinol and retinal (retinene). body cells synthesize this vitamin from a group of yellowish plant pigments, which are provitamins called carotenes. excess or its precursors are mainly stored in teh liver, which regulates their concentration in the body. an adult's liver stores enough vitamin A to supply body requirements for a year. infants and children usually lack such reserves and are more likely to develop deficiencies relatively stable to the effects of heat, acids, and bases but is readily destroyed by oxidation and is unstable in light. important in vision retinal is used to synthesize rhodopsin (visual purple) in the rods of the retina and light sensitive pigments in the cones. also functions in development of normal bones and teeth, and in maintenance of epithelial cells in skin and mucous membranes. vitamin A and beta carotenes also act as antioxidants by readily combining with oxygen and certain oxygen containing molecules that have unshared electrons, which makes them highly reactive and damaging to cellular structures these unstable molecules are called oxygen free radicals, and they accumulate in certain diseases and with age. liver, fish, whole milk, butter and eggs carotene is found in leafy green vegetables and in yellow or orange vegetables and fruits excess vitamin A: peeling skin, hair loss, nausea, headache, dizziness, inhibit growth and breakdown bones and joints, causes night blindness

Beta oxidation

first phase: fatty acids are activated. this change requires energy from ATP and a special group of enzymes called thiokinases. each of these enzymes can act upon a fatty acid that has a particular carbon chain length one fatty aid molecules have been activated, other enzymes called fatty acid oxidses in mitochondria break them down. this phase of the reactions removes successive two carbon segments of fatty acid chains. in the liver, some of these segments react to produce acetyl coenzyme A molecules. excess acetyl CoA molecules can be converted into compounds called ketone bodies, such as acetone, which later may be changed back to acetyl coenzyme A in either case, the resulting acetyl coenzyme A can be oxidized in the citric acid cycle. the glycerol parts of the triglyceride molecules can also enter metabolic pathways leading to the citric acid cycle, or they can be used to synthesize glucose.

vitamin D

fortified: essential nutrients have been added to a food where they originally were absent or scarce. enriched: essential nutrients have been partially replaced in a food that has lost nutrients during processing. excess (hypervitaminosis D): produces diarrhea, nausea, and weight loss. over time it may calcify certain soft tissues and irreversibly damage the kidneys deficiency: rickets, osteomalacia (bones decalcify and weaken due to disturbances in calcium and phosphorus metabolism 5 minutes in the sun two to three times a week can maintain skeletal health without elevating skin cancer risk.

Vitamin E

group of compounds, the most active of which is alpha tocopherol resistant to the effects of heat, acids, and visible light but is unstable in bases and in the presence of ultraviolet light or oxygen strong antioxidant found in all tissues but is primarily stored in the muscles and adipose tissue highly concentrated in the pituitary and adrenal glands precise functions of vitamin E are unknown but it is through to act as an antioxidant by preventing oxidation of vitamin A and polyunsaturated fatty acids in the tissues. it may also help maintain the stability of cell membranes widely distributed among foods. oils from cereal seeds, wheat germ, salad oils, margarine, shortenings, fruits, nuts, vegetables excess: nausea, headache, fatigue, easy bruising and bleeding, muscle weakness

Energy Requirements

maintaining the BMR usually requires the body's greatest expenditure of energy the energy required to support voluntary muscular activity comes next, though this amount varies greatly with the type of activity the energy to maintain posture while sitting at a desk might require 100 calories per hour above the basal need, whereas running or swimming might require 500-600 calories per hour maintenance of body temp may require additional energy expenditure, particularly in cold weather

Essential nutrients

nutrients that human cells cannot synthesize and that must be obtained in the diet (amino acids)

Vitamins

organic compounds (other than carbohydrates, lipids, and proteins) required in small amounts for normal metabolism that body cells cannot synthesize in adequate amounts. essential nutrients that must come directly from foods or indirectly from provitamins, which are precursor substances. classified on the basis of whether they are soluble in fats (or fat solvents) or in water. fat soluble vitamins are A, D, E, and K water soluble group includes the B vitamins and vitamin C

lipids

organic compounds that include fats, oils, fatlike substances (phospholipids, cholesterol) supply energy for cellular processes help build structures (cell membranes) most common dietary lipids are the fats called triglycerides

Insulin

pancreas stimulates adipocytes to admit glucose and store fat; glycogen synthesis

metabolism

refers to the ways that nutrients are altered chemically and used in anabolism and catabolism of chemical compounds to support the activities of life

LIpid Use

regulating circulating lipids, the liver controls the total amount of cholesterol in the body by synthesizing and releasing it into the blood or by removing cholesterol from the blood and excreting it into the bile. the liver uses cholesterol to produce bile salts. cholesterol is not used as an energy source, but it does provide structural material for cell and organelle membranes, and it furnishes starting materials for the synthesis of certain sex hormones and hormones produced by he adrenal cortex, adipose tissue stores excess triglycerides. if the blood lipid concentration drops (in response to fasting) some of these stored triglycerides are hydrolyzed into free fatty acids and glycerol and released into the bloodstream.

insulin

secreted from the pancreas, regulates fat stores by stimulating adipocytes to take up glucose and store fat by stimulating certain other cells to take up glucose and form glycogen

proteins

several pathways decompose the remaining deaminated parts of amino acids. the specific pathways that are followed depend upon the particular type of amino acid being dismantled some pathways form acetyl coenzyme A, and others more directly lead to steps of the citric acid cycle. as energy is released from the cycle, some of its is captured in molecules of ATP if energy is not required immediately, the deaminated parts of the amino acids may react to form glucose or fat molecules in other metabolic pathways. a few hours after a meal, protein catabolism, through the process of gluconeogenesis, becomes a major source of blood glucose. metabolism in most tissues soon shifts away from glucose and toward fat catabolism as a source of ATP energy needs are met in a way tha spares proteins for tissue building and repair, rather than being broken down and reassembled into carbohydrates to supply energy. using structural proteins to generate energy causes the tissue wasting of starvation.

factors influence food intake

smell taste texture neural signals triggered by stretch receptors in the stomach stress hormones

protein requirements

supplying essential amino acids proteins provide nitrogen and other elements for the synthesis of nonessential amino acids and certain non protein nitrogenous substances the amount of dietary protein individuals require varies according to body size, metabolic rate, and nitrogen balance condition average adult, nutritionists recommend a daily protein intake of about .8 gram per kilogram of body weight or 10% of a persons diet 60-150 grams per day average 30 grams for pregnant women 20 grams for nursing women protein deficiency causes tissue wasting and also decreases the level of plasma proteins, which decreases the colloid osmotic pressure of the plasma as a result fluids collect in the tissues, producing nutritional edema

Energy requirements

the BMR for an average adult indicates a requirement for approx 1 calorie of energy per hour for each kilogram of body weight this requirement varies with sex, body size, body temp, and level of endocrine gland activity. heat loss is directly proportional to the body surface area, and a smaller person has a greater surface area relative to body mass, he/she will have a higher BMR. males typically have higher metabolic rates than females as body temp, blood level of thyroxine, or blood level of epinephrine increase, so does the MBR. the BMR can also increase when the level of physical activity increases during the day.

Lipid requirements

the USDA and the American Heart Association recommend that lipid intake not exceed 30% of total daily calories fat intake must be sufficient throughout life to support absorption and transport of fat soluble vitamins. most adults who eat a variety of foods obtain adequate fats.

energy requirements

the amount of energy required to support metabolic activity for 24 hours varies from person to person the factors that influence individual energy needs include a measurement called the basal metabolic rate, the degree of muscular activity, body temp, and rate of growth the basal metabolic rate or BMR measures the rate at which the body expends energy under basal conditions--when a person is awake and at rest; after an overnight fast; and in a comfortable, controlled environment. test of thyroid function can be used to estimate a persons BMR the amount of oxygen the body consumes is directly proportional to the amount of energy released by cellular respiration the BMR indicates the total amount of energy expended in a given time to support the activities of such organs as the brain, heart, lungs, liver, and kidneys

Energy values of foods

the amount of potential energy a food contains is expressed as calories which are units of heat a calorie is defined as the amount of heat required to raise the temperature of a gram of water by 1 degree Celsius, the calorie used to measure food energy is 1,000 times greater. the large calorie equals the amount of heat required to raise the temperature of a kilogram of water by 1 Celsius and is also equal to 4.184 joules a joule is the international unit of heat and energy. a large calorie is also called a kilocalorie, caloric values determined in a bomb calorimeter are somewhat higher than the mount of energy that metabolic oxidation releases, because nutrients generally are not completely absorbed from the digestive tract. also, the body does not completely oxidize amino acids, but excretes parts of them in urea or uses them to synthesize other nitrogenous substances. when such losses are considered, cellular oxidation yields on the average about 4.1 calories from 1 gram of carbohydrate, 4.1 calories from 1 gram of protein, and 9.5 calories from 1 gram of fat. more than twice as much energy is derived from equal amounts by weight of fats as from either proteins or carbohydrates. this is one reason why avoiding fatty foods helps weigh loss, if intake of other nutrients does not substantially increase fats encourage weigh gain because they add flavor to food, which can cause overeating fatty foods satisfy hunger longer than carbohydrate foods

Lipid Use

the liver uses free fatty acids to synthesize triglycerides, phospholipids, and lipoproteins that may then be released into the bloodstream these lipoproteins are large and consist of a surface layer of phospholipid, cholesterol, and protein surrounding a triglyceride core. the protein constituents of lipoproteins in the outer layer, called apoproteins or apolipoproteins, can combine with receptors on the membranes of specific target cells. lipoprotein molecules vary in the proportions of the lipids they contain. lipids are less dense than proteins. as the proportion of lipids in a lipoprotein increases, the density of the particle decreases. as the proportion of lipids decreases the density increases lipoproteins are classified on the basis of their densities, which reflect their composition. very low density lipoproteins (VLDL) have a high concentration of triglycerides low density lipoproteins (LDL) have a high concentration of cholesterol and are the major cholesterol carrying lipoproteins high density lipoproteins (HDL) have a relatively high concentration of protein and a lower concentration of lipids.