Chapter 4: Carbohydrates

Plants Synthesize Glucose

Monosaccharides Structure Glucose Fructose Galactose

Fructose (fruit sugar) Metabolized to glucose in the liver Found in fruit, honey, and high fructose corn syrup Is in sucrose

Galactose Usually bound with glucose (lactose) Converted to glucose in the liver Available fuel source

Disaccharides “Simple sugars” Maltose (Gluc + Gluc) Fermentation Alcohol production Sucrose (Gluc + Fruc) Sugar Lactose (Galactose + Gluc) Milk products

Complex Carbohydrates Polysaccharides: Starch & Glycogen Amylose Amylopectin Dietary fiber

Oligosaccharides 3-10 monosaccharides Found in beans and legumes Not digested Metabolized by bacteria in the large intestine Beno®

Polysaccharides: Starch 3,000 or more monosaccharides bound together Starch Amylose--straight chain polymer Amylopectin--highly branched polymer

Glycogen Storage form of CHO for animals and human Structure similar to amylopectin More sites for enzyme action Found in the liver and muscles

Dietary Fiber Undigested plant food Body cannot break the bonds Insoluble fiber Cellulos, hemicellulose, lignin Not fermented by the bacteria in the colon Soluble fiber Gum, Pectin, Mucilage Fruit, vegetable, rice bran, psyllium seed

Soluble and Insoluble Fiber

Health Benefits of Dietary Fiber Absorbs and holds water Soften stool Larger stool promotes peristalsis Promotes regularity Lower risk for cardiovascular disease Decrease hemorrhoids and diverticula

Diverticula

CHO in Food

Sweeteners Sucrose--benchmark of all sweeteners Same caloric content (4 kcals/gm) No health benefit over another Consumption ranges: lbs/yr per person

Types of Sweeteners High-fructose corn syrup cornstarch treated with acid and enzymes conversion of glucose into fructose same degree of sweetness as sucrose cheaper and used in many food products Brown sugar Maple syrup Honey Sugar alcohols kcal/g Absorbed and metabolized slower Large amount causes diarrhea

Sugar Substitutes Saccharin First produced in x sweeter than sucrose Excessive intake is linked to bladder cancer in lab animals Not a potential risk in humans

Aspartame (NutraSweet) Composed of phenylalanine, aspartic acid, and methanol x sweeter than sucrose 4 kcal/gm, but only a trace amount is needed to sweeten foods Not heat stable Complaints of sensitivity to aspartame headaches, dizziness, seizures, nausea, etc. Not recommended for people with phenylketonuria (PKU)

Acesulfame-K (Sunette) Newest sugar substitute 200x sweeter than sucrose Not digested by the body Heat stable Diabetisweet used in baking

Sucralose (Splenda) 600x sweeter than sucrose Substitute chlorines for hydroxyl groups on sucrose Heat stable Tiny amount digested

Digestion

Effects of Cooking Softens fibrous tissues Easier to chew and swallow

Digestion of Carbohydrate in the Mouth Saliva contains amylase Starch is broken down to shorter saccharides Taste the sweetness with prolong chewing Proceeds down the esophagus

Digestion of Carbohydrate in the Stomach The acidic environment stops the action of salivary amylase No further starch digestion occurs

In the Small Intestine Pancreatic amylase is released Intestinal cells release enzymes Maltose + maltase glucose + glucose Sucrose + sucrase glucose + fructose Lactose + lactase glucose + galactose Monosaccharides are absorbed

CHO Digestion

CHO Absorption Glucose and Galactose Active absorption Energy is expended Going from low to high concentration gradient Fructose Facilitated diffusion using a carrier No energy expended

Portal Vein Transport absorbed monosaccarhides Delivers them to the liver Liver can: transform them into glucose release them back into the blood stream store as gylcogen (or fat)

Functions of Carbohydrate Supplies energy Protein sparing Prevent ketosis Sweetener

Regulation of Blood Glucose Hyperglycemia Hypoglycemia

Blood Glucose Control Role of the liver Regulates glucose that enters bloodstream Role of the pancreas Release of insulin Release of glucagon

Functions of Insulin Promotes glycogen synthesis Increases glucose uptake by the cells Reduces gluconeogenesis Net effect: lowers the blood glucose

Functions of Glucagon Breakdown glycogen Enhances gluconeogenesis Net effect: raises blood glucose

Epinephrine/ Norepinephrine “fight or flight” response breakdown glycogen raises blood glucose

Diabetes Mellitus-Type 1 Genetic link Decreased release of insulin Insulin dependent Hyperglycemia Immunological disorder Early introduction of cow’s milk

Treatment for Type 1 CHO counting Insulin therapy Risk for heart disease

Diabetes Mellitus-Type 2 Genetic link Associated with obesity Non-insulin dependent to start Accounts for majority of cases of DM Defective insulin receptors on the cells Over secretion of insulin to compensate Leads to beta cells failure Treatment: medication and diet therapy (weight loss)

Consequences of Uncontrolled Blood Glucose Ketosis leading to ion imbalances, dehydration, coma, death Degenerative diseases Nerve damage, Heart disease, Kidney disease, Blindness Atherosclerosis Increase risk for wound infections

Hypoglycemia Reactive hypoglycemia Occurs 2-4 hours after eating a meal Possibly due to over secretion of insulin Fasting hypoglycemia Usually caused by pancreatic cancer Leads to overproduction of insulin

Sweetener Function Enhances flavor Use in moderation

Recommended Intake No RDA (yet) Consume at least 50 gm to prevent ketosis National Cholesterol Education Program recommends 50-60% of kcal from CHO Current intake is ~50%

Health Benefits of Dietary Fiber--Recall Promotes softer, larger stool and regularity Slows glucose absorption Reduces blood cholesterol Reduces heart disease Reduces hemorrhoids and diverticula

Recommended Dietary Fiber Intake gm of fiber/day (10-13 gm/1000 kcals) Children: age +5gm/day Ave. U.S. intake: ~16 gm/day Too much fiber (>60 gm/d) will: require extra intake of fluid bind to some minerals develop phytobezoars fills the stomach of a young child quickly

Recommendation for Simple Sugar Intake Low nutrient density Recommends no more than 10% of total kcal/day Ave. U.S. intake: 16% of total kcal/day Added to food and beverages during processing

High Sugar Diets Empty calories Soda replacing milk Calories adding to excess Dental caries exposure to teeth High glycemic index Blood glucose response of a given food Influence by various factors

Effects of High Glycemic Index CHO Stimulates the release of insulin Insulin’s effect blood triglycerides level Insulin’s effect LDL Insulin increases fat synthesis Return to hunger quicker Develop insulin resistance

Lactose Intolerance Reduction in lactase Lactose is undigested and not absorbed Lactose is metabolized by large intestinal bacteria causes gas, bloating, cramping, discomfort Primary lactose intolerance disease Secondary lactose intolerance disease

What To Do If You Are Lactose Intolerance Determine amount you can tolerate Eat dairy with fat Cheese & yogurt are usually tolerated well Use of Lact-Aide