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Chapter 2 Carbohydrates Man shall not live by bread alone. Copyright © 2009, by Mosby, Inc. an affiliate of Elsevier, Inc. All rights reserved. 1 Key Concepts • Carbohydrate foods provide practical energy (calorie) sources because of their availability, relatively low cost, and storage capability. • Carbohydrate structures vary from simple to complex to provide both quick and extended energy for the body. Copyright © 2009, by Mosby, Inc. an affiliate of Elsevier, Inc. All rights reserved. 2 Classes of Carbohydrates • Monosaccharides – Simple sugar – Simple carbohydrate • Glucose • Fructose • Galactose Copyright © 2009, by Mosby, Inc. an affiliate of Elsevier, Inc. All rights reserved. 3 Classes of Carbohydrates, cont’d • Disaccharides – Double sugar – Simple carbohydrate • Sucrose (glucose and fructose) • Lactose (glucose and galactose) • Maltose (glucose and glucose) Copyright © 2009, by Mosby, Inc. an affiliate of Elsevier, Inc. All rights reserved. 4 Classes of Carbohydrates, cont’d • Polysaccharides – Starch – Glycogen – Dietary fiber Copyright © 2009, by Mosby, Inc. an affiliate of Elsevier, Inc. All rights reserved. 5 Starch • Most significant polysaccharide in the diet • Whole grains retain the bran layer, inner germ, and endosperm, including the nutrients naturally found in the plant • Enriched grains are refined grains that have nutrients added back to them Copyright © 2009, by Mosby, Inc. an affiliate of Elsevier, Inc. All rights reserved. 6 Other Sweeteners • Nutritive sweeteners – Sugar alcohols (sorbitol, mannitol, xylitol) • Non-nutritive sweeteners – Artificial sweeteners in food (Examples in next slide) Copyright © 2009, by Mosby, Inc. an affiliate of Elsevier, Inc. All rights reserved. 7 Sweetness of Sugars and Artificial Sweeteners Copyright © 2009, by Mosby, Inc. an affiliate of Elsevier, Inc. All rights reserved. 8 Focus on Dietary Fiber • Cellulose – Remains undigested in the gastrointestinal tract and provides bulk to a diet – Bulk helps move the food mass through the intestine (prevents constipaton) – Examples: • Stems, leaves of vegetables, corn hull, beans, coverings of seeds and grains Copyright © 2009, by Mosby, Inc. an affiliate of Elsevier, Inc. All rights reserved. 9 Focus on Dietary Fiber, cont’d • Noncellulose polysaccharides – Absorb water and swell to a larger bulk – Examples: pectins from fruit; gums & mucilages – secretions from plants like okra; algal substances - seaweed • Lignin – Only noncarbohydrate type of dietary fiber – Woody parts of plants (broccoli stems & seeds) Copyright © 2009, by Mosby, Inc. an affiliate of Elsevier, Inc. All rights reserved. 10 Focus on Dietary Fiber, cont’d • Divided into two groups based on solubility – Insoluble – Soluble • Many health organizations recommend increasing intake of dietary fiber **38 g/day for men **25 g/day for women Copyright © 2009, by Mosby, Inc. an affiliate of Elsevier, Inc. All rights reserved. 11 Focus on Dietary Fiber, cont’d • Sudden increases in fiber can result in gas, bloating, and constipation • Excessive amounts of dietary fiber can trap small amounts of minerals and prevent their absorption into the gastrointestinal tract Copyright © 2009, by Mosby, Inc. an affiliate of Elsevier, Inc. All rights reserved. 12 Summary of Dietary Fiber Classes Copyright © 2009, by Mosby, Inc. an affiliate of Elsevier, Inc. All rights reserved. 13 Energy Function of Carbohydrates • Basic fuel supply – Energy for physical activities and all work of body cells • Reserve fuel supply – Provided by stored glycogen – Available to maintain a normal blood glucose level Copyright © 2009, by Mosby, Inc. an affiliate of Elsevier, Inc. All rights reserved. 14 Special Tissue Functions of Carbohydrates • Liver – Stored glycogen protect cells from depressed metabolic function • Protein and fat – Carbohydrates regulate proteins and fat used for energy • Heart – Glycogen is vital emergency back up fuel for heart muscle Copyright © 2009, by Mosby, Inc. an affiliate of Elsevier, Inc. All rights reserved. 15 Digestible Food Sources of Carbohydrates • Central nervous system – Brain dependent on minute-to-minute supply of glucose • Starches – Provide fundamental complex carbohydrates • Sugars – Readily absorbed – High-sugar diets carry health risks Copyright © 2009, by Mosby, Inc. an affiliate of Elsevier, Inc. All rights reserved. 16 Teaspoons of High-Fructose Corn Syrup Consumed We eat too much sugar! Copyright © 2009, by Mosby, Inc. an affiliate of Elsevier, Inc. All rights reserved. 17 Digestion of Carbohydrates • Mouth – Mechanical or muscle functions break food mass into smaller particles – Chemical digestion begins with salivary amylase • Stomach – Peristalsis continues mechanical digestive process Copyright © 2009, by Mosby, Inc. an affiliate of Elsevier, Inc. All rights reserved. 18 Digestion of Carbohydrates, cont’d • Small intestine – Peristalsis continues mechanical digestion – Pancreatic secretions - Pancreatic amylase breaks starches down into disaccharides and monosaccharides – Intestinal secretions - Sucrase, lactase, and maltase help break down their starches Copyright © 2009, by Mosby, Inc. an affiliate of Elsevier, Inc. All rights reserved. 19 Body Needs for Carbohydrates • Dietary Reference Intakes – 45% to 65% of adult’s total caloric intake should come from carbohydrate foods – Limit sugar to no more than 25% of calories consumed Copyright © 2009, by Mosby, Inc. an affiliate of Elsevier, Inc. All rights reserved. 20 Summary • Carbohydrates are the primary source of energy for most of the world’s population. • Carbohydrates are distributed as the plant sources: grains, legumes, vegetables, and fruits. • The two basic types of carbohydrates are simple and complex. • Simple carbohydrates are composed of single- and double-sugar units (monosaccharides and disaccharides) Copyright © 2009, by Mosby, Inc. an affiliate of Elsevier, Inc. All rights reserved. 21 Summary, cont’d • Complex carbohydrates are composed of many sugar units. • Dietary fiber is a complex carbohydrate that is not digestible and is found mainly in the structural parts of plants. • Carbohydrate digestion begins in the mouth, continues in the stomach, moves to the small intestine, and finally arrives in the large intestine and exits through the anus. Copyright © 2009, by Mosby, Inc. an affiliate of Elsevier, Inc. All rights reserved. 22 FATS -Key Concepts • Dietary fat supplies essential body tissue needs, both as an energy fuel and a structural material. • Foods from animal and plant sources supply distinct forms of fat that affect health in different ways. • Excess dietary fat, especially from animal food sources, is a negative risk factor in overall health. Copyright © 2009, by Mosby, Inc. an affiliate of Elsevier, Inc. All rights reserved. 23 The Nature of Fats • Dietary importance – Concentrated fuel for energy • Classes of fats – Lipids – Glycerides • Triglycerides – Fatty acids – Lipoproteins Copyright © 2009, by Mosby, Inc. an affiliate of Elsevier, Inc. All rights reserved. 24 Fatty Acids • ESSENTIAL fatty acids means that it is ESSENTIAL that we eat them • Saturated fatty acids – Filled or “saturated” with hydrogen • Unsaturated fatty acids – Omega 3 and omega 6 – Not completely filled with hydrogen – Less heavy, less dense – Monounsaturated: one unfilled spot – Polyunsaturated: two or more unfilled spots Copyright © 2009, by Mosby, Inc. an affiliate of Elsevier, Inc. All rights reserved. 25 Phospholipids • Triglyceride derivative: third fatty acid replaced by phosphate group • Partially hydrophobic, partially hydrophilic – remember cell wall? • Allow transport of fats through bloodstream Copyright © 2009, by Mosby, Inc. an affiliate of Elsevier, Inc. All rights reserved. 26 Cholesterol • Not a fat • A fat-related compound – Only from animal foods • Egg yolks • Liver, kidney • Meats – Synthesized in the liver – Diet should be low in cholesterol – Linked with heart disease Copyright © 2009, by Mosby, Inc. an affiliate of Elsevier, Inc. All rights reserved. 27 Functions of Fat in Foods • Fat in foods provide: – Energy – Essential nutrients – Flavor and satisfaction – Fat substitutes are not absorbed and therefore do not provide energy or essential nutrients but may provide flavor and satisfaction Copyright © 2009, by Mosby, Inc. an affiliate of Elsevier, Inc. All rights reserved. 28 Functions of Fat in the Body • Adipose tissue – Protects organs – Helps regulate temperature • Cell membrane structure – Forms part of cell membrane – Helps transport nutrients across cell membranes • Second choice to achieve energy Copyright © 2009, by Mosby, Inc. an affiliate of Elsevier, Inc. All rights reserved. 29 Food Sources of Fat • Animal fats • Plant fats • Hydrogenated fats (trans fats) – Commercial fat products raise health concerns – Food industry now offers trans-free products Copyright © 2009, by Mosby, Inc. an affiliate of Elsevier, Inc. All rights reserved. 30 A QUESTION FOR YOU! • Why are trans fats “worse” than saturated fats? • Studies show they lower HDL cholesterol and raise LDL cholesterol, whereas saturated fats only raise LDL cholesterol, leaving HDL the same or better Copyright © 2009, by Mosby, Inc. an affiliate of Elsevier, Inc. All rights reserved. 31 FDA Health Claims • Claims that link one or more dietary components to the reduced risk of a specific disease need to be approved by the FDA – Fat and cancer – Saturated fat and cholesterol and heart disease Copyright © 2009, by Mosby, Inc. an affiliate of Elsevier, Inc. All rights reserved. 32 Key Concepts • Dietary fat supplies essential body tissue needs, both as an energy fuel and a structural material. • Excess dietary fat, especially from animal food sources, is a negative risk factor in overall health. Copyright © 2009, by Mosby, Inc. an affiliate of Elsevier, Inc. All rights reserved. 33 Dietary Fat and Health • The American diet is high in fat. • Excess calories are stored as fat. • Animal food sources contribute to excess cholesterol and saturated fat in the diet. • A decrease in saturated fat reduces serum total cholesterol. • Monounsaturated fats reduce LDL cholesterol when substituted for saturated fat. Copyright © 2009, by Mosby, Inc. an affiliate of Elsevier, Inc. All rights reserved. 34 Digestion of Fats • Mouth - mechanical • Stomach - mechanical • Small intestine – chemical & mechanical – Bile from the gallbladder – Enzymes from the pancreas – Enzymes from the small intestine – Absorption Copyright © 2009, by Mosby, Inc. an affiliate of Elsevier, Inc. All rights reserved. 35 Dietary Fat Requirements • Healthy diet guidelines: – Stress the health benefits of a diet low in fat overall, but more so with saturated fat, and cholesterol – Recommend that the fat content should not exceed 20% to 35% of total kilocalories • Less than 10% of kilocalories should be from saturated fat • Dietary cholesterol should be limited to 300 mg/day Copyright © 2009, by Mosby, Inc. an affiliate of Elsevier, Inc. All rights reserved. 36 Dietary Guidelines for Americans • Control saturated fat and cholesterol • Use only lean cuts of all meats; use more poultry and seafood (shellfish are low in fat but high in cholesterol) • Limit eggs to two or three per week – Can discard the yolk to decrease fat • Use low-fat or fat-free milk and milk products • Avoid adding too much fat in food preparation – food should not slide across the plate! Mosby items and derived items © 2006 by Mosby, Inc. Copyright © 2009, by Mosby, Inc. an affiliate of Elsevier, Inc. All rights reserved. 37 Slide 37 Summary • Classes of fat include lipids, triglycerides, fatty acids, and lipoproteins • Fatty acids can be saturated or unsaturated • Essential fatty acids are necessary to aid in tissue strength, muscle tone, cholesterol metabolism, blood clotting, and heart action Copyright © 2009, by Mosby, Inc. an affiliate of Elsevier, Inc. All rights reserved. 38 Summary, cont’d • Cholesterol is a sterol only found in animal foods that is vital in human metabolism • Digestion of fat includes digestive agents such as bile and pancreatic lipase • Fatty acids and glycerides are incorporated into chylomicrons and absorbed via the lymphatic system into the bloodstream Copyright © 2009, by Mosby, Inc. an affiliate of Elsevier, Inc. All rights reserved. 39