Chapter 4- Carbohydrates

Citric Acid Cycle

- Acetyl-CoA enters the citric acid cycle, where two carbons are lost as carbon dioxide, high-energy electrons are released, and a small amount of ATP is produced.

The Role of Alternative Sweeteners

- Alternative sweeteners can be used to reduce the amount of added sugar in the diet. - They do not contribute to tooth decay and can help keep blood sugar in the normal range. - They reduce the energy content of the diet if the calories they eliminate are not added back in other food choices.

Types of Nonnutritive Sweeteners

- Alternative sweeteners that provide no calories are often referred to as nonnutritive sweeteners and include saccharin, aspartame, sucralose, acesulfame K, and rebiana.

Why Fiber May Protect against Colon Cancer

- Cells in the colon may be exposed to carcinogens in the colon contents. - Fiber may help reduce the risk of colon cancer by decreasing the amount of contact between the cells lining the colon and these carcinogenic substances.

Complex Carbohydrates

- Complex carbohydrates are generally not sweet to the taste like simple carbohydrates.

How Indigestible Carbohydrates Affect Nutrient Absorption

- Fiber binds certain minerals, such as zinc, calcium, iron, and magnesium, preventing their absorption. - Soluble fiber binds cholesterol and bile, thus reducing their absorption. - In the stomach, fiber causes distention and slows gastric emptying, thus increasing satiation.

Monosaccharides

- Glucose (aka blood sugar) is a monosaccharide that is the primary form of carbohydrate used to provide energy in the body. - Fructose (aka fruit sugar) is a monosaccharide that is the primary form of carbohydrate found in fruit. - Galactose is a monosaccharide that combines with glucose to form lactose.

Glycogen

- Glycogen, the storage form of glucose in animals, is a highly branched chain of glucose molecules that can be broken down quickly for energy. - There is a limited amount glycogen stores in the body. Glycogen is stored on the liver and muscles - liver glycogen is used to maintain blood glucose - muscle glycogen supplies glucose for exercising muscles

Carbohydrate Digestion and Absorption

- In the mouth, the enzyme salivary amylase starts breaking starch into shorter polysaccharides. - In the stomach, salivary amylase is inactivated by acid so no carbohydrate digestion occurs. - In the small intestine, pancreatic amylase completes the job of breaking down starch into disaccharides and oligosaccharides. - At the villi of the small intestine, enzymes attached to the microvilli complete the digestion of disaccharides and oligosaccharides into the three monosaccharides. - In the large intestine, fiber and other indigestible, or resistant, carbohydrates are partially broken down by bacteria to form short-chain fatty acids and gas.

Disaccharides

- Maltose is a disaccharide composed of two glucose molecules that is formed in the intestines during starch digestion. - Sucrose (aka table sugar) is a disaccharide formed by linking fructose and glucose. - Lactose (aka milk sugar) is a disaccharide formed by linking a glucose molecule with a galactose, and is only naturally found in animal products.

Electron Transport Chain

- Most ATP is produced in the final step of cellular respiration, the electron transport chain. - Here, the energy from the high-energy electrons released in the previous steps pumps hydrogen ions across the inner mitochondrial membrane. - As the hydrogen ions flow back, the energy is used to convert ADP to ATP, and the electrons are combined with oxygen and hydrogen to form water.

Why Protein Is Broken Down to Supply Blood Glucose

- Since adequate dietary carbohydrate eliminates the need to use amino acids from protein (skeletal muscle) to synthesize glucose through gluconeogenesis, carbohydrate is said to "spare protein".

Fibers

- Soluble fibers dissolve in water or absorb water to form viscous solutions and can be broken down by the intestinal microflora. They include pectin, gums, and some hemicelluloses. - Insoluble fibers are those that do not dissolve in water and cannot be broken down by bacteria in the large intestine. They include cellulose, lignin, and some hemicelluloses. - Whole grains, legumes, fruits, and vegetables are good sources of fiber.

Making and Breaking Sugar Chains

- Sugars are made through a condensation reaction, which will release a water molecule. - Sugars are broken down through a hydrolysis reaction, which requires a water molecule.

How Much Total Carbohydrate?

- The RDA for carbohydrate for adults and children is 130 g per day. - Guidelines for healthy diets recommend 45 to 65% of energy from carbohydrates and a fiber intake of 25 g and 38 g, respectively for females and males.

Translating Recommendations into Healthy Diets

- The typical North American diet includes about 50% of calories coming from carbohydrate with most coming from refined sources. - Our average fiber intake is only 15 g per day, which is well below the AI.

Supplying Glucose to Body Cells

- To ensure a steady supply of glucose to body cells, blood glucose levels are maintained within normal limits by the liver and the hormones insulin and glucagon. - When blood glucose rises, insulin is released from the pancreas, allowing muscle and adipose tissue cells to take up the glucose. - When blood glucose falls, glucagon is released to increase blood glucose by signaling glycogen to break down into glucose.

Why Lactose Intolerance Causes GI Distress

- Undigested lactose passes into the colon where it draws in water and is metabolized bacteria, producing gas and acids and causing abdominal distension, flatulence, cramping, and diarrhea.

What Types of Carbohydrates Are Recommended?

- Unrefined carbohydrates are good sources of fiber. - There is no RDA or Daily Value for added sugars, however, consumption needs to be limited to less than 10% of the energy coming from added sugars.

How Refined and Unrefined Carbohydrates Differ

- Unrefined sources of carbohydrates, such as whole grains, legumes, vegetables, fruits, and milk contain a variety of nutrients and phytochemicals with much of the fiber, vitamins, and minerals lost in the refining process. - Whole grain products contain all three of the major components of the grain kernel: the endosperm, bran, and germ. - Enriched grains contain added thiamin, riboflavin, niacin, and iron and are fortified with folate.

What Happens When Carbohydrate is Limited?

- When carbohydrate is limited, metabolism must shift to make sure that glucose is available to the brain and other cells that require glucose as an energy source.

Carbohydrates and Health

A dietary pattern that is high in unrefined carbohydrates has been associated with a lower incidence of a variety of chronic diseases, whereas diets high in refined carbohydrates may contribute to chronic disease risk.

Why We Should Limit Added Sugars

Added refined sugars provide energy, but few nutrients, thus lowering the nutrient density of the diet.

Delivering Glucose to Body Cells

After absorption, the monosaccharides travel to the liver via the hepatic portal vein. - Once in the liver, fructose and galactose are converted into glucose and used in one of three ways: for immediate energy, put into storage as glycogen, or converted into fatty acids for long-term storage.

How Cancer Cells Differ from Normal Cells

Cancer cells differ from normal cells because they divide without restraint and are able to grow in areas reserved for other cells.

Carbohydrates in the Body

Carbohydrate is an important source of energy for body cells

Types of Carbohydrates

Carbohydrates are chemical compounds that contain carbon, hydrogen, and oxygen.

Carbohydrates and Weight Management

Carbohydrates contribute to weight gain when total energy intake exceeds needs

Exercise

Exercise increases the sensitivity of body cells to insulin so that glucose is available to fuel exercising muscles as well as promoting weight loss.

Indigestible Carbohydrates

Fiber, some oligosaccharides, and resistant starch are not broken down by human digestive enzymes in the stomach and small intestine, and therefore, pass into the colon.

Gestational Diabetes

Gestational diabetes is a form of diabetes that occurs in women during pregnancy that disappears once the pregnancy is complete

How Glucose Provides Energy

Glucose is metabolized through cellular respiration to generate ATP.

What Affects Glycemic Response?

How quickly or how high blood glucose rises after carbohydrate is consumed is referred to as glycemic response; Glycemic response can be quantified by using the glycemic load or glycemic index.

Hypoglycemia

Hypoglycemia is a condition in which blood sugar drops low enough to cause symptoms including irritability, nervousness, sweating, shakiness, anxiety, rapid heartbeat, headache, and hunger. - Hypoglycemia is a common complication of diabetes treatment.

Medication

In Type 1 diabetes, insulin must be injected while with those with Type 2 diabetes, oral hypoglycemic agents are taken.

Glycolysis

In the cytosol of the cell, glycolysis (anaerobic metabolism) splits glucose into two molecules of pyruvate. - Glycolysis produces high-energy electrons and two molecules of ATP per glucose. - Each pyruvate is either broken down to produce more ATP or used to make glucose via gluconeogenesis.

Acetyl-CoA Formation

In the mitochondria in the presence of oxygen, one carbon is removed from pyruvate and released as carbon dioxide. - The remaining two-carbon compound combines with a coenzyme A (CoA) to form acetyl CoA, which enters the citric acid cycle.

How Indigestible Carbohydrates Affect Transit Time

Indigestible carbohydrates increase the volume of material in the lumen of the intestine, thus adding bulk or weight to the stool.

Indigestible Carbohydrates and Bowel Health

Indigestible carbohydrates make the stool larger and softer, thus reducing the pressure needed to move material through the colon. - Indigestible carbohydrates, then, lower the risk of constipation, hemorrhoids, and the symptoms of diverticular disease.

Diet

Individuals with diabetes can use exchange lists or a system of carbohydrate counting to estimate and control the amount of carbohydrate consumed with each meal. The food groups that contain carbohydrate are: vegetables, fruits, starch, and dairy. These are the food groups to monitor. The diet should not be low in fat as low fat diets (high in carbohydrate) will further increase blood levels of glucose and insulin. The diet should be moderate in healthy fats.

Why Ketones Are Formed

Ketones are molecules formed in the liver when there is not sufficient carbohydrate to completely metabolize the two-carbon units produced from fat breakdown.

Why Low-Carbohydrate Diets Promote Weight Loss

Low-carbohydrate diets lead to less food being consumed (carbohydrate is in many foods) - They also cause ketosis, which suppresses appetite, and therefore, food intake, leading to weight loss.

Lactose Intolerance

Not enough lactase to digest lactose

Oligosaccharides

Oligosaccharides, short-term carbohydrates containing 3 to 10 sugar units, can be formed in the gut during the breakdown of polysaccharides.

Simple Carbohydrates

Simple carbohydrates include mono and disaccharides and are founds in foods, such as table sugar, honey, and milk

Carbohydrates in Our Food

Some carbohydrates in our diets are from unrefined foods, such as whole grains, fruits, and vegetables while others are from refined grain sources like white breads and baked goods.

Indigestible Carbohydrates and Colon Cancer

Some people are more susceptible to cancer due to genetics, but the development of most cancers is believed to be influenced by environmental carcinogens, or cancer-causing agents.

Starches

Starch is the storage form of carbohydrates in plants

Carbohydrate Recommendations

Sufficient carbohydrate is needed daily to maintain blood glucose. Obtaining carbohydrate from vegetables and fruits will also increase phytonutrient intake.

Sugar Alcohols

Sugar alcohols are sweeteners that are structurally related to sugars, but provide less energy because they are not well absorbed.

Carbohydrates in the Digestive Tract

Sugars and starches consumed in food are broken down in the digestive tract to monosaccharides, which can be absorbed into the bloodstream.

How Diabetes Is Treated

The goal of diabetes treatment is to keep blood glucose levels within the normal range through diet, exercise, and medication.

Immediate Symptoms

The immediate symptoms of diabetes may include excessive thirst, frequent urination, blurred vision, and weight loss.

Long-Term Complications

The long-term complications of diabetes include damage to the heart, blood vessels, kidneys, eyes, and nerves. This is due to excessive blood levels of insulin and glucose.

Dental Caries

The most well-documented health problem associated with a diet high in carbohydrates is dental caries, or tooth cavities. - Bacteria in the mouth can form colonies that stick to the teeth. - When carbohydrates - particularly simple carbohydrates - are consumed, they are metabolized by the bacteria, producing acids that dissolve the tooth enamel, forming dental caries.

Why Indigestible Carbohydrates Increase Intestinal Gas

The oligosaccharides raffinose and stachyose are usually the culprits of the increase in intestinal gas after consuming beans

Why Diabetes Causes Symptoms and Complications

The symptoms and complications of diabetes result from the fact that, without sufficient insulin, glucose cannot be used normally.

Type 1 Diabetes

Type 1 diabetes is an autoimmune disease in which the body's own immune system destroys the insulin-secreting cells of the pancreas.

Type 2 Diabetes

Type 2 diabetes occurs when the body does not produce enough insulin to keep blood glucose in the normal range because insulin receptors have decreased function. The blood levels of insulin will be higher than "normal" but as the insulin receptors are not working properly, the blood glucose will rise. - Type 2 diabetes is often preceded by a condition called "prediabetes" or impaired glucose tolerance

Why Indigestible Carbohydrates Promote a Healthy Microflora

When the indigestible carbohydrates reach the colon, they serve as food source for the bacteria there

Carbohydrate Functions

While the main function of glucose is to provide energy to body cells, each of the saccharides has other specific functions, such as cell communication, and to synthesize DNA and RNA

Carbohydrates and Heart Disease

diets high in carbohydrate can increase heart disease risk by raising blood lipid levels.