Carbohydrates Chapter 2

1. CarbohydratesChapter 2

2. Carbohydrates • More than just “sugar” and “starch” • Provide the majority of calories in almost all human diets • Carbohydrate classifications • Carbohydrates • Class of energy-yielding nutrients that contain only carbon, hydrogen, and oxygen, hence the common abbreviation of CHO • Simple carbohydrates contain only 1 or 2 sugar molecules • Complex carbohydrates contain many sugarmolecules

3. Carbohydrates (cont’d) • Carbohydrate classifications (cont’d) • Monosaccharides • Simplest of all sugars • Most common • Glucose • Fructose • Galactose

4. Carbohydrates (cont’d) • Carbohydrate classifications (cont’d) • Monosaccharides (cont’d) • Glucose • Also known as dextrose • Component of all disaccharides • Sugar into which the body converts all other digestible carbohydrates

5. Carbohydrates (cont’d) • Carbohydrate classifications (cont’d) • Monosaccharides (cont’d) • Fructose or “fruit sugar” • Sweetest of all natural sugars • High-fructose corn syrup (HFCS) • Galactose • Does not occur in appreciable amounts in foods • Combines with glucose to form lactose

6. Carbohydrates (cont’d) • Carbohydrate classifications (cont’d) • Disaccharides • Made of two linked monosaccharides • Sucrose, maltose, and lactose are disaccharides • Sucrose or “sugar” • Composed of glucose and fructose • Differences among sugars is degree of refining • Occurs naturally in some fruits and vegetables

7. Carbohydrates (cont’d) • Carbohydrate classifications (cont’d) • Disaccharides (cont’d) • Maltose • Composed of two joined glucose molecules • Not found naturally in foods • Lactose or “milk sugar” • Composed of glucose and galactose • Found naturally in milk • What does it do? • Least sweet of all sugars

8. Question • Is the following statement true or false? Another name for glucose is dextrose and is the sugar into which the body makes all digestible carbohydrates.

9. Answer True. Rationale: Glucose, also known as dextrose, is the sugar of greatest distinction. It circulates through the blood to provide energy for body cells; it is a component of all disaccharides and is virtually the sole constituent of complex carbohydrates; and it is the sugar into which the body converts all other digestible carbohydrates.

10. Carbohydrates (cont’d) • Carbohydrate classifications (cont’d) • Polysaccharides • Complex carbohydrates • Do not taste sweet • Starch, glycogen, and fiber are types of polysaccharides

11. Carbohydrates (cont’d) • Carbohydrate classifications (cont’d) • Polysaccharides (cont’d) • Starch • Glucose not used by plants stored as starch • Grains • World’s major food crop • Foundation of all diets • Potatoes, dried peas and beans, and other starches

12. Carbohydrates (cont’d) • Carbohydrate classifications (cont’d) • Polysaccharides (cont’d) • Glycogen • Animal (including human) version of starch • Liver glycogen releases glucose into the bloodstream to maintain blood sugar between meals • No dietary source of glycogen

13. Carbohydrates (cont’d) • Carbohydrate classifications (cont’d) • Polysaccharides (cont’d) • Fiber • Generally considered a group name for polysaccharides that cannot be digested by human enzymes • Commonly referred to as “roughage” • Categorized as insoluble or soluble • “Dietary” fiber • “Functional” fiber • Commonly assumed that fiber does not provide any calories • Source of energy for colon lining

14. Carbohydrates (cont’d) • Sources of carbohydrates • Grains, Vegetables, Fruits, and Milk are the MyPyramid groups that provide the majority of carbohydrates • Nuts and dried peas and beans • Oils group • Grains • Synonymous with “carbs” • Classified as “whole” or “refined”

15. Carbohydrates (cont’d) • Sources of carbohydrates (cont’d) • Grains (cont.) • Whole grains • Consist of the entire kernel of a grain • Can be cracked, ground, or milled into flour • Composed of 3 parts: • The bran • The endosperm • The germ (embryo)

16. Carbohydrates (cont’d) • Sources of carbohydrates (cont’d) • Grains (cont’d) • “Refined” grains • Rich in starch, but lack the fiber, vitamins, trace minerals, fat, and phytochemicals found in whole grains • Enrichment • Required to be fortified • Examples include white flour, white bread, white rice, and refined cornmeal

17. Carbohydrates (cont’d) • Sources of carbohydrates (cont’d) • Vegetables • Starch and some sugars provide the majority of calories in vegetables • “Starchy” vegetables provides 3 times more carbohydrate than the same amount of “watery” vegetables

18. Carbohydrates (cont’d) • Sources of carbohydrates (cont’d) • Fruits • Almost all of the calories in fruit come from sugar (mostly fructose), with small amounts of starch and minute quantities of protein providing negligible calories • Exceptions to this are avocado, olives, and coconut, which get the majority of their calories from fat • Fiber is located in the skin of fruits

19. Carbohydrates (cont’d) • Sources of carbohydrates (cont’d) • Milk • One cup of milk provides 12 g of carbohydrate in the form of lactose • Cottage cheese, which has about 6 g of carbohydrate per cup • Discretionary calories • “Extras” • Carbohydrate content varies

20. Carbohydrates (cont’d) • How the body handles carbohydrates • Digestion • Cooked starch begins to undergo digestion in the mouth by the action of salivary amylase • Most carbohydrate digestion occurs in the small intestine • Disaccharidase enzymes split disaccharides into monosaccharides • Monosaccharides are the only form of carbohydrates the body is able to absorb intact • 95% of starch is digested usually within 1 to 4 hours after eating

21. Carbohydrates (cont’d) • How the body handles carbohydrates (cont’d) • Absorption • Sugars absorbed through intestinal mucosa cells • Undigested starch passes with stools • Fibers may impair the absorption of some minerals—namely calcium, zinc, and iron—by binding with them in the small intestine

22. Carbohydrates (cont’d) • How the body handles carbohydrates (cont’d) • Metabolism • Fructose and galactose are converted to glucose in the liver • Liver releases glucose to maintain blood sugar level • Rise in blood sugar causes pancreas to release insulin • Postprandial state • Blood glucose concentration begins to drop • Pancreas releases glucagon • Stimulates liver to release glucose

23. Carbohydrates (cont’d) • How the body handles carbohydrates (cont’d) • Glycemic response • Increase in blood glucose levels • Glycemic index • Determined by comparing the impact on blood glucose after 50 g of a food sample is eaten compared to the impact of 50 g of pure glucose or white bread • May help diabetics and athletes

24. Carbohydrates (cont’d) • How the body handles carbohydrates (cont’d) • Glycemic response (cont’d) • Glycemic load • More accurately define a food’s impact on blood glucose levels • Not reliable for choosing healthy diet • Functions of carbohydrates • Glucose metabolism = balance between catabolism and anabolism

25. Carbohydrates (cont’d) • How the body handles carbohydrates (cont’d) • Functions of carbohydrates (cont’d) • Glucose for energy • Primary function of carbohydrates is to provide energy for cells • Brain is totally dependent on glucose for energy • Spares protein and prevent ketosis • Protein sparing • Need to consume adequate carbohydrates

26. Carbohydrates (cont’d) • How the body handles carbohydrates (cont’d) • Functions of carbohydrates (cont’d) • Preventing ketosis • Without adequate glucose, fat oxidation prematurely stops at the intermediate step of ketone body formation • Increased production of ketones causes nausea, fatigue, loss of appetite, and ketoacidosis • Dehydration and sodium depletion may follow

27. Carbohydrates (cont’d) • Using glucose to make other compounds • Glycogen • Body’s backup supply of glucose • One third of the body’s glycogen reserve is in the liver • Nonessential amino acids • Carbohydrate-containing compounds • Fat

28. Carbohydrates (cont’d) • Dietary reference intakes • Total carbohydrate • The RDA for carbohydrates is set at 130 g for both adults and children • Acceptable macronutrient distribution range • Fiber • Adequate intake for total fiber is set at 14 g/ 1000 • Sugar • Maximal level of 25% of total calories or less from added sugars is recommended

29. Question • When the body does not have an adequate intake of glucose, the formation of ketone bodies increases. Increased production of ketones has several side effects. What is one of these side effects? a. Increased appetite b. Potassium depletion c. Nausea and vomiting d. Sodium depletion

30. Answer d. Sodium depletion Rationale: An increased production of ketone bodies and their accumulation in the bloodstream causes nausea, fatigue, loss of appetite, and ketoacidosis. Dehydration and sodium depletion may follow as the body tries to excrete ketones in the urine.

31. Carbohydrates in Health Promotion • Concentrate on fiber and whole grains • Most consistent benefit of consuming adequate fiber is to relieve or prevent constipation • Linked to a decreased risk of heart disease, cancer, diabetes, and obesity • Dietary guidelines recommend that adults and children consume at least one half of their grain servings from whole grains • Results in 20% to 30% lower risk of atherosclerotic cardiovascular disease

32. Carbohydrates in Health Promotion (cont’d) • Concentrate on fiber and whole grains (cont’d) • Dietary guidelines (cont’d) • Less likely to develop insulin resistance and metabolic syndrome, common precursors of type 2 diabetes • Associated with improved body weight management • Tips for choosing whole grains • On average, Americans eat one serving per day of whole grains • Factors contributing to the low intake of whole grains include consumers’ inability to identify whole grains, a lack of awareness of their health benefits, and the cost, taste, and unfamiliarity with how to prepare whole grains

33. Carbohydrates in Health Promotion (cont’d) • How to increase dietary fiber: • Replace refined grains with whole grains • Choose a ready-to-eat cereal with 5 g of fiber or more per serving • Eat dried peas and beans 2 to 3 times per week • Eat at least 5 servings of fruits and vegetables daily • Eat a variety of plant foods daily • Increase fiber intake gradually to avoid GI intolerance • Consume adequate fluid

34. Carbohydrates in Health Promotion (cont’d) • Limit added sugars • Sugar adds flavor and interest • Inaccurately blamed for a variety of health problems • Limiting intake is prudent • Sugar alternatives • Sugar alcohols • Nonnutritive sweeteners

35. Carbohydrates in Health Promotion (cont’d) • Limit added sugars (cont’d) • Sugar alternatives (cont’d) • Sugar alcohols • Sorbitol, mannitol, and xylitol • Natural sweeteners derived from monosaccharides • Most are commercially synthesized • Incompletely absorbed • Side effects • Offer sweetness without promoting cavities

36. Carbohydrates in Health Promotion (cont’d) • Limit added sugars (cont’d) • Sugar alternatives (cont’d) • Nonnutritive sweeteners • Virtually calorie free • Sweeter than sugar • Do not raise blood glucose levels • Risks and benefits of nonnutritive sweeteners • Weight management • Diabetes mellitus • Safety

37. Carbohydrates in Health Promotion (cont’d) • Take steps to avoid dental caries • Choose between-meal snacks that are healthy and teeth-friendly • Limit between-meal carbohydrate • Avoid high-sugar items • Brush promptly after eating • Chew gum sweetened with sugar alcohols • Use fluoridated toothpaste

38. Question • A diabetic diet is now based more on keeping the total carbohydrate intake consistent with less emphasis on the source of the carbohydrate. What has this change in focus meant for diabetic diets? a. Sugar alternatives are substituted for simple sugars. b. Sweets can be included in the diabetic diet. c. Calorie control is most important for diabetics. d. Diabetics need to learn the glycemic load of foods.

39. Answer b. Sweets can be included in the diabetic diet. Rationale: Contrary to what was previously believed, regular sugar does not raise blood glucose levels more than complex carbohydrates do; a food’s glycemic load is influenced by several factors, not just sugar content. The focus in management of blood glucose levels has shifted from avoiding simple sugars to maintaining a relatively consistent total carbohydrate intake with less emphasis on the source. For that reason, sweets can be included within the context of a nutritious, calorie-appropriate, carbohydrate-controlled diet.

40. Carbohydrates in Health Promotion (cont’d) • The most common sources of added sugars in the American diet: • Soft drinks • Cakes, cookies, and pies • Fruit drinks and punches • Dairy desserts such as ice cream • Candy

41. Carbohydrates in Health Promotion (cont’d) • Sugar: too much of a good thing • Behavioral problems in children • Obesity • Diabetes mellitus • Heart disease