Chapter 4 Carbohydrates Plants Synthesize Glucose Simple Sugars

Chapter 4: Carbohydrates

Plants Synthesize Glucose

Simple Sugars Monosaccharides Single sugar molecules Disaccharides Pairs of monosaccharides

Monosaccharides Glucose Fructose Galactose

Glucose (Dextrose) Not used as a sweetener Source: breakdown of starch and other sugars

Glucose in the Body Form of sugar found in the blood Only energy source for the brain Quick energy for muscles

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

Galactose Not used as sweetener Usually bound with glucose (lactose or milk sugar) Converted to glucose in the liver Available fuel source

Disaccharides: Pairs of Sugars “Simple sugars” Linked monosaccharides Always contain glucose

Sucrose Glucose + Fructose Table sugar Soft drinks, candy, ice cream Baked goods, jelly, cereal

Lactose Galactose + Glucose Dairy products Increases calcium absorption

Maltose (malt sugar) Glucose + Glucose Sprouting seeds Digestion of starch Fermentation Alcohol production

Complex Carbohydrates Polysaccharides: Starch & Glycogen Amylose: straight chain digestible starch Amylopectin: branched chain digestible starch Dietary fiber: non-digestible

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

Polysaccharides: Starch 3, 000 or more monosaccharides bound together Plant storage of glucose Two forms Amylose--straight chain polymer l Amylopectin--highly branched polymer l

Polysacchairides

Sources of Starch Grain products: bread, cereal, pasta Some “starchy” vegetables: corn, peas, carrots, potatoes

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

Glycogen Sources Dietary: insignificant Made in the body Stored in the liver and muscles

Dietary Fiber Plant cells Cannot be digested by humans Humans lack necessary enzymes to break the bonds

Dietary Fiber Found only in plants Whole grains Fruits Vegetables

Types of Fiber Insoluble fiber Cellulose, hemicellulose, lignin Does not dissolve in water Not fermented by bacteria in the colon Tough, fibrous parts of vegetables Cereal bran, whole grains, fruit

Types of Fiber Soluble fiber Gum, Pectin, Mucilage Fermented in colon Sources: Fruits, vegetables, oats, beans, rice bran, psyllium seed

Soluble and Insoluble Fiber

Health Benefits of Insoluble Fiber Decreases intestinal transit time Promotes regularity, softer stools Reduces constipation Reduces risk of hemorrhoids (varicose veins in the rectum) caused by constipation

Health Benefits of Insoluble Fiber Reduces risk of diverticulosis Outpouching of intestinal wall l Diverticulitis: inflamed pouches l High fruit and vegetable intake seems to reduce risk of colon cancer, though fiber may not be the factor

Diverticula

Health Benefits of Soluble Fiber Associated with reduced risk of cardiovascular disease Slows absorption of glucose from the small intestine Appears to reduce risk of diabetes May help with blood glucose control (but requires very large amounts of fiber)

Health Benefits of All Fiber Weight management Bulky, high-fiber foods fill you up Have low energy density May reduce risk of obesity

Negative Effect of Excessive Fiber >60 g/day Bind minerals (calcium, zinc, iron) Satiety without adequate nutrients, especially in children Diarrhea Constipation: if inadequate water can result in bowel obstruction

CHO in Food

Carbohydrate 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

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

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

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 fructose/galactose into glucose release them into the blood stream store as gylcogen (or fat)

Uses of Glucose Energy Brain’s only source Muscle – quick energy Glycogen Muscle: used by individual muscle Liver: maintain blood sugar Excess converted to fat Stored in fat cells Future energy use as fat

Regulation of Blood Glucose Hyperglycemia l Hormone regulates l Insulin Hypoglycemia l Hormones regulate l Glucagon l Epinephrine

Blood Glucose Control Role of the liver l Regulates glucose that enters bloodstream Role of the pancreas l Release of insulin l 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 of 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 Immunological disorder Associated with early introduction of cow’s milk Absence of insulin Insulin dependent Hyperglycemia

Treatment for Type 1 CHO counting Insulin therapy Risk for heart disease, kidney damage, other complications

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 Poor Blood Glucose Control Acute: Hypoglycemia; Ketosis leading to ion imbalances, dehydration, coma, death Chronic Nerve damage Heart disease Kidney disease Blindness Atherosclerosis Wound infections Amputations

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

Sweeteners Sucrose--benchmark of all sweeteners Same caloric content (4 kcals/gm) No health benefit over another Consumption ranges: 14 -48 lbs/yr person

Types of Sweeteners High-fructose corn syrup l l 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 l l l 1. 5 -3 kcal/g Absorbed and metabolized slower Large amount causes diarrhea

Low Calorie Sweeteners Saccharin (Sweet’N Low®) Aspartame (Nutra. Sweet®) Acesulfame potassium, acesulfame-K (Sweet One®) Sucralose (SPLENDA®) Neotame

Saccharin First produced in 1879 180 -200 x sweeter than sucrose Excessive intake is linked to bladder cancer in lab animals Not a potential risk in humans in amounts normally used

Aspartame (Nutra. Sweet) Composed of phenylalanine and aspartic acid 180 -200 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 l headaches, dizziness, seizures, nausea, etc. Not recommended for people with phenylketonuria (PKU)

Aspartame (Nutra. Sweet) FDA recommended limits 50 mg/kg body weight/day in adults =14 cans diet soft drink 80 packets Equal

Acesulfame-K (Sunette) FDA approved 1988 200 x sweeter than sucrose Not digested by the body Heat stable Diabetisweet used in baking; gum, Kool-Aid, puddings, gelatin, candy

Sucralose (Splenda) FDA approved 1998 600 x sweeter than sucrose Substitute chlorines for hydroxyl groups on sucrose Heat stable Tiny amount digested Used in soft drinks, gum, baked goods, frozen desserts, fruit drinks

Sweetener Function Enhances flavor Use in moderation

CHO 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%

Recommended Fiber Intake Choose fiber-rich fruits, vegetables, and whole grains often (2005 US Dietary Guidelines) Adults ≤ 50 years 38 grams (men) and 25 grams (women). Adults >50 who eat less food, 30 grams (men); 21 grams (women). (U. S. DRIs) Children >1 years: AI’s range from 19 g (age 1 -3) 25 g (4 -8); adolescent boys 31 -38 g; adolescent girls 26 g The Average American eats 14 -15 grams of fiber a day

Recommended Dietary Fiber Intake 20 -35 gm of fiber/day (10 -13 gm/1000 kcals) Children: age +5 gm/day Ave. U. S. intake: ~16 gm/day Too much fiber (>60 gm/d) will: l l 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 Displaces other foods 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

Names for Added Sugars that Appear on Food Labels

Major Sources of Added Sugar (Caloric Sweeteners) in the American Diet

Sugar and ADD/ADHD There is no evidence that sugar is a cause of ADD/ADHD or exacerbates symptoms

U. S. Dietary Guidelines Choose and prepare foods and beverages with little added sugars or caloric sweeteners Reduce the incidence of dental caries by practicing good oral hygiene and consuming sugar and starchcontaining foods and beverages less frequently

Glycemic Index The blood glucose response of a given food compared to a standard (typically glucose or white bread)

Glycemic Index The concept of Glycemic Index has been highlighted in popular diet books Sugar Busters l The South Beach Diet l

Glycemic Index Influenced by various factors Starch structure Fiber content Cooking methods Degree of processing Whether it is eaten in the context of a meal Presence or absence of fat A given food can elicit highly variable responses

Glycemic Index of Selected Foods Food Brown rice White long grain rice GI 55 56 White short grain rice 72 Spaghetti Whole Wheat bread 41 69 White bread Sucrose Carrots Potatoes, mashed 70 65 49 73 -83 Wardlaw. Contemporary Nutrition, p. 134

Glycemic Index Epidemiological studies suggest that high glycemic index diets are associated with health consequences such as increased risk for diabetes However, the American Diabetes Association states the total amount of CHO is more important than the GI Combining low GI foods with high GI foods at meals will reduce blood glucose response

Functions of CHO Provide energy 4 kcals/gram l Brain, nerves, red blood cells l With low cho intake, proteins converted to glucose l Protein-sparing l ~100 g CHO/day

Functions of CHO Source of fiber Indigestible plant cells l Health benefits l Adds flavor, texture, color l Makes food appetizing Needed for proper fat metabolism l Avoid ketosis

Functions of Carbohydrate Supplies energy Protein sparing Prevent ketosis Sweetener