CARBOHYDRATES Chapter 5

Carbohydrates Made of carbon, hydrogen, and oxygen in a 1:2:1 ratio Primary fuel source for body cells Divided into two main classes: Simple sugars Complex sugars

MONOSACCHARIDES

GLUCOSE Also called hexose or dextrose Principle building block of all other carbohydrates Typically exists in the ring form

FRUCTOSE Also called levulose Isomer of glucose Metabolized into glucose by the liver Small amounts are converted into glycogen, lactic acid, or fat Found in fruit, honey, and high fructose corn syrup

GALACTOSE Not usually found free in nature in large quantities Isomer of glucose Typically found as a subunit of lactose Converted to glucose by the liver Used as an immediate energy source or is stored as glycogen

Other Monosaccharides Ribose Five carbon sugar Used in the formation of RNA Very little present in our diet Deoxyribose Used in the formation of DNA Not considered a nutrient of our diet since our bodies can make all that it ever needs.

DISACCHARIDES

MALTOSE Constructed by a condensation reaction Composed of two glucose molecules Possesses an alpha bond Commonly produced by fermentation reactions called malting Most maltose digested is the result of starch digestion

SUCROSE Constructed by a condensation reaction Composed of one glucose and one fructose Possesses an alpha bond Commonly called table sugar and is found in plants such as sugar cane and maple syrup Purified to form brown, white, and powdered sugars

LACTOSE Constructed by a condensation reaction Composed of one glucose and one galactose Possesses a beta bond Beta bonds are difficult to digest Primary sugar in milk and milk products

OLIGOSACCHARIDES 3-10 monosaccharides: raffinose and stachyose Found in beans and legumes Not digested by the body Metabolized by bacteria in the large intestine Raffinose=galactose+glucose+fructose Stachyose=galactose+galactose+ glucose+fructose

POLYSACCHARIDES Digestible polysaccharides: Starch Amylose Amylopectin Glycogen Non-digestible polysaccharides: fibers Soluble fiber Insoluble fiber

STARCHES 3000 monosaccharides Contain alpha bonds Amylose is straight chain Amylopectin is branched chain High Glycemic Index

GLYCOGEN Storage form of glucose in animals and humans Structure is similar to amylopectin but with more complex branching Numerous alpha bonds Found in liver (400 kcal) and muscles (1400 kcal)

Fiber Dietary fiber= fibers found naturally in foods Functional fibers= fiber added to foods that has shown to provide health benefits Total fiber= dietary fiber + functional fiber

Chemical Composition of Fibers Contain beta bonds Insoluble: not fermented Cellulose Hemicellulose Lignin* Soluble: 1.5-2.5 kcal/g Gum Pectin Mucilage

Fibers

Carbohydrate Digestion

Within the Mouth Saliva contains amylase Converts polysaccharides, starch, into oligosaccharides, maltose, and glucose Broken down by hydrolysis reaction

Within the Stomach The acidic environment of the stomach inhibits the action of salivary amylase

Within the Small Intestines Pancreatic amylase Converts oligosaccharides to disaccharides Intestinal cells release Maltase Lactase Sucrase

CARBOHYDRATE ABSORPTION Monosaccharide absorption occurs in the duodenum Glucose and galactose by active absorption Fructose by facilitated diffusion

CARBOHYDRATE ABSORPTION Portal vein transports absorbed monosaccharides to the liver Liver can then: Transform them to glucose Release them back to the blood stream Store it as glycogen

FUNCTIONS OF CARBOHYDRATES Supplies energy Protein sparing Prevents ketosis Food sweeteners Fructose Sucrose Glucose Maltose Galactose

FUNCTIONS OF DIETARY FIBER Promotes regularity and softer, larger stool Reduces hemorrhoids and diverticula

DIVERTICULOSIS

FUNCTIONS OF DIETARY FIBER Promotes regularity and softer, larger stool Reduces hemorrhoids and diverticula Aids weight control Causes a filling of fullness Slows glucose absorption Decrease in colon cancer Reduces cholesterol absorption Reduces heart disease

RECOMMENDED CARBOHYDRATE INTAKE RDA is 130 g/day for adults 50-100 g of CHO/day to prevent ketosis Recommended: 45-65% of total kcal 180-330 g of CHO/day (primarily from white bread, soda, baked goods) 50% of total kcal Worldwide the CHO intake is +70%

RECOMMENDED FIBER INTAKE Adequate Intake is 25 g/day for women and 38 g/day for men (14g/1000kacl) Daily Value= 25g/day for 2000 kcal diet Average U.S. intake= 13-17 g/day

Sample Menus

Sample Menus

PROBLEMS WITH HIGH SUGAR INTAKES Empty calories Dental caries Glycemic index=the blood glucose response to a given food compared to a standard Glycemic load=the amount of Carbohydrate in food times the glycemic index for that food. Related to structure, fiber content, amount of processing, and macronutrient content

Effects of Ingesting High Glycemic Load Foods Stimulates insulin release Insulin increases blood triglyceride levels Insulin increases LDL Insulin increase fat synthesis Increased risk for CVD Muscles may become resistant to insulin Increases risk of developing diabetes Become hungry quicker

PROBLEMS WITH HIGH INTAKES OF DIETARY FIBER Too much fiber (>60 g/day) will: Require extra intake of fluids Bind to some vitamins Develop phytobezoars Fill the stomach of a young child quickly

Lactose Maldigestion Primary lactose maldigestion 75% of world population Begins to develop around age 3 to 5 years Secondary lactose maldigestion Temporary decrease in lactase production 25% of North American population Increases with age

FOOD SWEETENERS Nutritive sweeteners Alternative sweeteners Sugars Sugar alcohols Alternative sweeteners Saccharin Aspartame Neotame Acesulfame-K Sucralose

Read the Nutrition Perspective Pp 171-176