Carbohydrates: Plant-Derived Energy Nutrients 4 Carbohydrates: Plant-Derived Energy Nutrients

What Are Carbohydrates? One of the three macronutrients Important source of energy for all cells Preferred energy source for nerve cells Composed of carbon, hydrogen, oxygen Good sources: fruits, vegetables, grains

What Are Carbohydrates? Glucose The most abundant carbohydrate Produced by plants through photosynthesis

What Are Carbohydrates? Simple carbohydrates Contain one or two molecules Commonly referred to as sugars Monosaccharides contain one molecule Glucose, fructose, and galactose Disaccharides contain two molecules Lactose, maltose, and sucrose

What Are Carbohydrates? Complex carbohydrates Oligosaccharides contain 3 to 10 monosaccharides Most polysaccharides consist of hundreds to thousands of glucose molecules Starch, glycogen, most fibers

Complex Carbohydrates Starch Plants store carbohydrates as starch Amylose—straight chain of glucose Amylopectin—branched chain of glucose Resistant starch (fiber)—glucose molecules linked by beta bonds are largely indigestible Sources: grains, legumes, fruits, vegetables

Complex Carbohydrates Glycogen Storage form of glucose for animals (humans) Not found in food and therefore not a source of dietary carbohydrate Stored in the liver and muscles

Complex Carbohydrates Fiber Composed of long polysaccharide chains Dietary fibers are non-digestible parts of plants Functional fibers are non-digestible forms of carbohydrates extracted from plants or manufactured in a laboratory and have known health benefits Total fiber = Dietary fiber + Functional fiber

Complex Carbohydrates Soluble fibers Dissolve in water; viscous and gel-forming Fermentable, digested by intestinal bacteria Associated with risk reduction of cardiovascular disease and type 2 diabetes Examples: pectin, gum, mucilage Found in citrus fruits, berries, oats, beans

Complex Carbohydrates Insoluble fibers Do not dissolve in water, nonviscous Cannot be fermented by bacteria in the colon Promote regular bowel movements, alleviate constipation, and reduce diverticulosis Examples: lignins, cellulose, hemicelluloses Good sources: whole grains, seeds, legumes, fruits, and vegetables ABC Video Whole Grains

Carbohydrate Digestion Salivary amylase Enzyme that begins carbohydrate digestion in the mouth Breaks carbohydrates down to maltose Carbohydrate digestion does not occur in the stomach Stomach acids inactivate salivary amylase Carbohydrate Digestion

Carbohydrate Digestion Most chemical digestion of carbohydrates occurs in the small intestine Pancreatic amylase Enzyme produced in the pancreas and secreted into the small intestine Digests carbohydrates to maltose

Carbohydrate Digestion Additional enzymes in the microvilli digest disaccharides to monosaccharides Maltase Sucrase Lactase Monosaccharides are absorbed into the cells lining the small intestine and then enter the bloodstream

Carbohydrate Digestion All monosaccharides are converted to glucose by the liver Glucose circulating in the blood is our primary energy source Excess glucose is stored as glycogen in the liver and muscles

Carbohydrate Digestion We do not have the enzymes necessary to digest fiber Bacteria in the large intestine can break down some fiber Most fiber remains undigested and is excreted in the feces Carbohydrate Absorption

Blood Glucose Regulation Blood glucose must be closely regulated Hormones control blood glucose levels: Insulin Glucagon Epinephrine Norepinephrine Cortisol Growth hormone Hormonal Control of Blood Glucose

Blood Glucose Regulation: Insulin Secreted by beta cells of the pancreas Stimulates glucose transporters (carrier proteins) to help take glucose from the blood across the cell membrane Stimulates the liver to take up glucose and convert it to glycogen

Blood Glucose Regulation: Glucagon Secreted by alpha cells of the pancreas Stimulates the liver to convert glycogen to glucose Stimulates gluconeogenesis, the production of glucose from amino acids

Blood Glucose Regulation: Epinephrine and Norepinephrine Secreted by the adrenal glands and nerve endings when blood glucose is low Increase glycogen breakdown in the liver, releasing glucose into the blood Responsible for our “fight-or-flight” reactions to danger

Blood Glucose Regulation: Cortisol and Growth Hormone Secreted by the adrenal glands to act on the liver, muscle, and adipose tissue Cortisol increases gluconeogenesis and decreases muscle glucose use Growth hormone decreases muscle glucose uptake, increases fatty acid mobilization and use, and increases liver glucose output

Blood Glucose Regulation: Glycemic Index A food’s potential to raise blood glucose Foods with a high glycemic index cause a sudden surge in blood glucose, triggering a large increase in insulin, which may be followed by a dramatic fall in blood glucose Foods with a low glycemic index cause low to moderate fluctuations in blood glucose

Blood Glucose Regulation: Glycemic Index Not always easy to predict Food’s absorption rate varies with type of carbohydrate, preparation methods, and its fat and fiber content Most foods are eaten in combination in a meal

Blood Glucose Regulation: Glycemic Load Used to determine the effect of a food on a person’s glucose response Grams of carbohydrates in a food are multiplied by the glycemic index Glycemic index and glycemic load remain controversial Evidence of health benefits is weak

Blood Glucose Regulation: Value of Lower Glycemic Index Less fluctuations in blood glucose Risk reduction for heart disease and colon cancer High fiber intake helps to improve fat levels in the blood (higher HDL and lower LDL) Foods with lower glycemic index: Beans, fresh vegetables, whole wheat

The Role of Carbohydrates Energy Each gram of carbohydrate: 4 kcal Red blood cells use only glucose for energy Both carbohydrates and fats supply energy for daily activities Glucose is especially important for energy during exercise

The Role of Carbohydrates Ketosis Fat breakdown during fasting forms ketones Excess ketones increase blood acidity and cause ketoacidosis Sufficient energy from carbohydrates prevents ketone production as alternate energy source Fad Diets

Carbohydrates Spare Protein Gluconeogenesis occurs when a diet is deficient in carbohydrate The body will make its own glucose from protein Amino acids from these proteins cannot be used to make new cells, repair tissue damage, support the immune system, or perform any of their other functions

Complex Carbohydrates Have Health Benefits Fiber May reduce the risk of colon cancer Helps prevent hemorrhoids, constipation, and other intestinal problems May reduce the risk of diverticulosis May reduce the risk of heart disease May enhance weight loss May lower the risk of type 2 diabetes Diverticulosis and Fiber

How Much Carbohydrate? Recommended Dietary Allowance (RDA) is 130 grams/day to supply adequate glucose to the brain Acceptable Macronutrient Distribution Range (AMDR) is 45% to 65% of daily calories Focus on fiber-rich carbohydrate foods

Simple Carbohydrates Diets high in simple sugars: Can cause tooth decay May increase “bad cholesterol” May decrease “good cholesterol” May contribute to obesity ABC Video Sugar and Processed Food

Complex Carbohydrates Most Americans eat too little complex carbohydrates Enriched foods are foods in which nutrients that were lost during processing have been added back so the food meets a specified standard Fortified foods have nutrients added that did not originally exist in the food (or existed in insignificant amounts)

Complex Carbohydrates Adequate Intake (AI) for fiber 25 g per day for women 38 g per day for men, or 14 g of fiber for every 1,000 kcal per day It is best to get fiber from food (also a source of vitamins and minerals) An adequate fluid intake (at least 8 oz/day) with high-fiber diets is recommended

Alternative Sweeteners Nutritive sweeteners Sucrose, fructose, honey, and brown sugar contain 4 kcal energy per gram Slow-absorbing sugar alcohols: 2−3 kcal/gm Non-nutritive (alternative) sweeteners Provide little or no energy Safe for adults, children, people with diabetes

Alternative Sweeteners Saccharin Acesulfame-K Aspartame Sucralose Truvia and PureVia (stevia plant)

Diabetes Inability to regulate blood glucose levels Type 1 diabetes Gestational diabetes Uncontrolled diabetes can cause nerve damage, kidney damage, blindness, and can be fatal

Diabetes—Type 1 Accounts for 10% of all cases Body does not produce enough insulin Causes hyperglycemia (high blood glucose) Requires insulin injections May be an autoimmune disease

Diabetes—Type 2 Insulin insensitivity (insulin resistance): cells become less responsive to insulin Metabolic syndrome: a cluster of risk factors that increase the risk for type 2 diabetes Once known as adult-onset diabetes Increasing in children and adolescents

Diabetes—Type 2 Cause is unclear, but genetics, obesity, and physical inactivity play a role Treat with weight loss, healthy eating, regular exercise, and, if necessary, medications Healthy lifestyle choices may prevent or delay the onset of type 2 diabetes

Hypoglycemia Low blood glucose may cause shakiness, sweating, anxiety, weakness Reactive hypoglycemia: pancreas secretes too much insulin after a high-carbohydrate meal Fasting hypoglycemia: pancreas produces too much insulin, even when someone has not eaten

Lactose Intolerance Insufficient enzyme lactase to digest the lactose-containing foods GI symptoms: gas, cramping, diarrhea Variations in extent of intolerance Not to be confused with milk allergy Need alternate sources of calcium