Role in Wellness

Nature has provided us with an excellent source of energy: carbohydrates. Found primarily in plants, carbohydrates are a convenient and economical source of calories for people throughout the world. Carbohydrates are organic compounds composed of carbon, hydrogen, and oxygen. These compounds consist of simple carbohydrates, such as glucose and sucrose, and complex carbohydrates, which include starch and dietary fiber. Each type of carbohydrate serves a distinct role in nourishing the body.

In addition to serving as an energy source, some carbohydrates are also used as sweetening agents. When carbohydrate sweeteners are found naturally in foods, such as in fruits, they are accompanied by essential nutrients. The sweetness makes eating nutrient-dense foods even more enjoyable. Some carbohydrates also supply dietary fiber.

The energy value of carbohydrates was discovered in 1844.¹ Recognition that increasing our consumption of carbohydrates from grains, vegetables, and fruits provides preventive health benefits is more recent. Increased levels of complex carbohydrates, particularly dietary fiber, appear to reduce the risk factors associated with chronic diet-related disorders such as heart disease, diabetes, and some cancers.² The Acceptable Macronutrient Distribution Range (AMDR) for carbohydrate is 45% to 65% of kcal intake per day as primarily complex carbohydrates.² The Dietary Guidelines concur, recommending that we emphasize a plant-based diet including fruits, vegetables, cooked dried beans and peas, whole grains, and seeds.³ This advice is reflected in MyPyramid. Although recommendations vary based on individual needs, average suggestions of two cups of fruits, two and one half cups of vegetables, and 6 ounces of grains (bread, cereal, rice, and pasta) provide adequate amounts of complex carbohydrates (Box 4-1).

BOX 4-1   MyPlate

Carbohydrates

www.choosemyplate.gov provides a wealth of resources about nutrients, foods, portions sizes, and activity levels related to caloric needs. Highlights of carbohydrate food sources are listed here, but do explore the MyPlate site at www.choosemyplate.gov to customize the information to individual needs.

Carbohydrate food sources include the following:

• Grains: Cereals, breads, crackers, rice, or pasta, at least half as whole grains (see following chart)

• Vegetables: Fiber-rich vegetables, starchy vegetables such as carrots, sweet potatoes, white potatoes, peas; legumes or dry beans such as kidney beans, chickpeas, and black-eyed peas

• Fruits: Fiber-rich fruits, most fruits especially bananas, grapes, pears, apples

• Milk: Fat-free or low fat milk, yogurt, and other milk products containing lactose (does not include most cheeses)

• Meats and beans: Replace animal sources with servings of legumes or dry beans

For each of the nutrient categories studied, a MyPlate section will be included to emphasize the importance of portion sizes for the five food categories. For carbohydrates, the focus is on portions of grains.

What Counts as an Ounce-Equivalent of Grains?*

In general, 1 slice of bread; 1 cup of ready-to-eat cereal; or cup of cooked rice, cooked pasta, or cooked cereal can be considered 1 ounce-equivalent from the grains group.

The following table lists specific amounts that count as 1 ounce-equivalent of grains toward your daily recommended intake. In some cases, the number of ounce-equivalents for common portions also is shown.

GRAIN	TYPES AND EXAMPLES	AMOUNT THAT COUNTS AS 1 OUNCE-EQUIVALENT OF GRAINS	COMMON PORTIONS AND OUNCE-EQUIVALENTS
Bagel	WG: whole wheat RG: plain, egg	1 mini bagel	1 large bagel = 4 ounce-equivalents
Biscuit	RG: baking powder/buttermilk	1 small (2-inch diameter)	1 large (3-inch diameter) = 2 ounce-equivalents
Bread	WG: 100% whole wheat RG: white, wheat, French, sourdough	1 regular slice 1 small slice French 4 snack-size slices rye	2 regular slices = 2 ounce-equivalents
Crackers	WG: 100% whole wheat, rye RG: saltines, snack crackers	5 whole wheat crackers 2 rye crispbreads 7 square or round crackers
English muffin	WG: whole wheat RG: plain, raisin	muffin	1 muffin = 2 ounce-equivalents
Muffin	WG: whole wheat RG: bran, corn, plain	1 small (-inch diameter)	1 large (-inch diameter) = 3 ounce-equivalents
Oatmeal	WG	cup cooked 1 packet instant 1 ounce dry (regular or quick)
Pancakes	WG: whole wheat, buckwheat RG: buttermilk, plain	1 pancake (-inch diameter) 2 small pancakes (3-inch diameter)	3 pancakes (-inch diameter) = 3 ounce-equivalents
Popcorn	WG	3 cups, popped	1 microwave bag, popped = 4 ounce-equivalents
Ready-to-eat breakfast cereal	WG: toasted oat, whole-wheat flakes RG: corn flakes, puffed rice	1 cup flakes or rounds cups puffed
Rice	WG: brown, wild RG: enriched, white, polished	cup cooked 1 ounce dry	1 cup cooked = 2 ounce-equivalents
Pasta (spaghetti, macaroni, noodles)	WG: whole wheat RG: enriched, durum	cup cooked 1 ounce dry	1 cup cooked = 2 ounce-equivalents
Tortillas	WG: whole wheat, whole grain corn RG: flour, corn	1 small flour tortilla (6-inch diameter) 1 corn tortilla (6-inch diameter)	1 large tortilla (12-inch diameter) = 4 ounce-equivalents

RG, Refined grains; WG, whole grains. This is shown when products are available both in whole grain and refined grain forms.

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^*Accessed June 14, 2012, from www.choosemyplate.gov/food-groups/carbohydrates-count.html.

Considering carbohydrates through the health dimensions provides perspective on their role in wellness. The physical health dimension depends on our ability to provide our bodies with enough carbohydrate kcal for energy and enough complex carbohydrates and fiber consumption for optimum body functioning. Issues related to the role of carbohydrates are often in the headlines. Our ability to process research findings and make decisions about our food choices reflects our level of intellectual, or reasoning, health dimension. For some of us, emotional health may depend on the ability to distinguish hypoglycemic (low blood glucose) symptoms. If we are aware of our personal response to normal hypoglycemia, can we then distinguish real emotional issues from those caused by hypoglycemia? The social health dimension also may be tested. Social groups can support change or make changes more difficult to achieve. Will you or your client feel comfortable snacking on a banana (a good fiber source) while chocolate bars are unwrapped? The spiritual health dimension has ties to carbohydrates because several religions view bread, a carbohydrate, as the “staff of life.”

Food Sources

The carbohydrates we consume are primarily from plant sources. As plants grow, they capture energy from the sun and chemically store it as carbohydrates. This process, called photosynthesis, depends on water from the earth, carbon dioxide from the atmosphere, and chlorophyll in the plant leaves to form carbohydrates.

All carbohydrates are organic compounds composed of carbon, hydrogen, and oxygen in the form of simple carbohydrates or sugars (Figure 4-1). When linked together, these simple sugars form three sizes of carbohydrates: monosaccharides, disaccharides, and polysaccharides (Figure 4-2).

Monosaccharides are composed of a single carbohydrate unit. Glucose, fructose, and galactose are monosaccharides. Disaccharides consist of two single carbohydrates bound together. Sucrose, maltose, and lactose are disaccharides.

Polysaccharides consist of many units of monosaccharides joined together. Starch and fiber are food sources of polysaccharides, whereas glycogen is a storage form in the liver and muscles.

The three sizes of carbohydrates are divided into two classifications: simple carbohydrates (monosaccharides and disaccharides) and complex carbohydrates (polysaccharides) (Table 4-1). Both are valuable sources of carbohydrate energy. There are differences, however, between the health values of simple and complex carbohydrates found in the foods we consume. Although simple carbohydrates primarily provide energy in the form of glucose, fructose, and galactose, complex carbohydrates also may provide fiber in addition to glucose.

Carbohydrates provide energy, fiber, and naturally occurring sweeteners (sucrose and fructose). Energy is the only real nutrient function of carbohydrates; the roles of fiber and carbohydrate sweeteners are discussed later in this chapter. Carbohydrates supply energy in the most efficient form for use by our bodies. If enough carbohydrate is provided to meet the energy needs of the body, protein can be spared or saved to use for specific protein functions. This service of carbohydrates is called the protein-sparing effect.

When adequate amounts of carbohydrates are available, both carbohydrates and small amounts of fats are used for energy. When there are not enough carbohydrates available, fat is metabolized, which results in the formation of ketones, intermediate products of fat metabolism. The body without distress easily disposes of low levels of ketones. If carbohydrate levels continue to be insufficient to meet energy demands, increased levels of ketones overwhelm the physiologic system and ketoacidosis develops; ketoacidosis affects the pH balance of the body, which can be lethal if uncontrolled. Although lipids and proteins can, if necessary, provide energy for most bodily needs, the brain and nerve tissues function best on glucose from carbohydrates.

Digestion and Absorption

Our food sources of carbohydrates tend to be disaccharides (sugars) and polysaccharides (starches). The gastrointestinal (GI) tract has the role of digesting carbohydrates into monosaccharides for easy absorption. The digestive process begins in the mouth. Mechanical digestion breaks food into smaller pieces and mixes the carbohydrate-containing food with saliva, which contains amylase, called ptyalin. This begins the hydrolysis of starch into the simpler carbohydrate intermediary forms of dextrin and maltose. In the small intestine, intestinal enzymes and specific pancreatic amylase work on starch intermediary products to continue the breakdown to monosaccharides.

Cultural Considerations

The Missing Enzyme

Many adults throughout the world are unable to easily digest the lactose found in milk. Approximately 75% of the adult world population and 25% of the U.S. population are lactose maldigesters. This condition, lactose intolerance, occurs when the body does not produce enough lactase, a digestive enzyme that breaks lactose into glucose and galactose. When the lactose sits in the large intestine, bacteria begin to ferment the undigested lactose, causing diarrhea, bloating, and increased gas formation.

Lactase deficiency may be the result of a primary or secondary cause. Primary lactose intolerance is caused by a genetic factor that limits the ability to produce lactase. Although small amounts of lactose can often be tolerated, the level of lactase produced cannot be enhanced. The condition is common among Asian/Pacific Islanders (Asian Americans), Africans (African Americans), Hispanics (Hispanic Americans), Latinos, and Native Americans. In the United States the prevalence of lactose intolerance caused by maldigestion or low lactose levels is approximately 75% in African Americans and Native Americans, 90% in Asian/Pacific Islanders, 50% in Hispanic Americans, and least common among whites.

One explanation for primary lactose intolerance is that the ability to digest milk is an age-related ability. Consider that the milk of mammals, including humans, was intended for the young to consume during periods of major growth. The ability to digest milk may diminish because the biologic need is lessened as maturity is reached. Older adults may also develop lactose intolerance as the aging process diminishes the production of some digestive enzymes such as lactase. The recent identification of a genetic variation is valuable for future diagnostic testing to determine risk for and severity of lactose intolerance earlier in life.

Sometimes secondary lactose intolerance occurs when a chronic gastrointestinal illness affects the intestinal tract, reducing the amount of lactase produced (see Chapter 17). Even a bout of an intestinal virus or flu can cause temporary lactose intolerance. Most of these individuals recover and are again able to digest lactose.

Application to nursing: Health professionals can guide clients to determine what amounts of lactose-containing foods can be tolerated despite low lactase levels. Fine-tuning eating styles may require the assistance of a registered dietitian (RD) to ensure adequate consumption of calcium-containing foods. Depending on the severity of the sensitivity, advice to clients may include additional label reading for lactose-containing foods and medications especially for clients dealing with conditions such as irritable bowel syndrome.

Data from Matthews SB et al: Systemic lactose intolerance: A new perspective on an old problem, Postgrad Med J 81(953):167-173, 2003; National Institutes of Health: Lactose intolerance, National Institutes of Health Pub No 03-2751, Washington, DC, 2003, National Digestive Diseases Information Clearinghouse; and Ridefelt P, Hakansson LD: Lactose intolerance: Lactose tolerance test versus genotyping, Scan J Gastroenterol 40(7):822-826, 2005.

Teaching Tool

Lacking Lactose? No Problem!

Lactose intolerance is not an illness and should not undermine a person’s sense of wellness. To ensure that clients receive an adequate supply of nutrients usually consumed in lactose-containing dairy products—especially calcium, riboflavin, and vitamin D—without the use of supplements, consider suggesting the following to clients:

• Experiment with different portion sizes of lactose-containing foods to determine individual levels of tolerance; small amounts up to cup consumed throughout the day can often be tolerated.

• Use over-the-counter lactase-enzyme tablets when consuming dairy products (presently available as Lactaid, Lactrase, Dairy Ease, and others).

• If available, purchase lactose-reduced dairy products such as milk, ice cream, and soft cheeses.

• Consume foods high in nutrients found in lactose-containing foods; high-calcium foods include broccoli, eggs, kale, spinach, tofu, shrimp, canned salmon, sardines with bones, and calcium-fortified orange juice.

• Consume hard cheeses (in moderate amounts because of fat content) that contain lower lactose levels such as Swiss, cheddar, Muenster, Parmesan, Monterey, and provolone.

• Avoid softer cheeses (or experiment to learn level of tolerance), including ricotta, cottage cheese, mozzarella, Neufchatel, and cream cheese (see Appendix L for lactose content of foods).

• Test tolerance of different brands of yogurt; lactose levels may vary according to processing variations. Generally, lactase bacteria in yogurt culture hydrolyse some of the lactose.

• Consider supplementation if these dietary modifications are not achieved; consult with a nutritionist for an appropriate supplement.

Enzymes specific for disaccharides (lactase for lactose, sucrase for sucrose, maltase for maltose) are secreted by the small intestine’s brush border cells, which then hydrolyze disaccharides into monosaccharides. (For more information, see the Cultural Considerations box, The Missing Enzyme, and the Teaching Tool box, Lacking Lactose? No Problem!) After an active absorption process (i.e., one that requires energy input), absorptive cells in the small intestine take up these monosaccharides. Once glucose, fructose, and galactose enter the villi, the portal blood circulatory system transports them to the liver. The liver removes fructose and galactose and converts them to glucose. This glucose may be used immediately for energy or for glycogen formation, a storage form of carbohydrate providing an always-ready source of energy. Figure 4-3 summarizes carbohydrate digestion.

Glucose, often called blood sugar, is the form of carbohydrate most easily used by the body. It is the simple carbohydrate that circulates in the blood and is the main source of energy for the central nervous system and brain. Glucose is rapidly absorbed into the bloodstream from the intestine, but it needs insulin to be taken into the cells, where energy is released.

Fructose is the sweetest of the sugars. Although fruits and honey contain a mixture of sugars, including sucrose, fructose provides the characteristic taste of fruits and honey. After absorption from the small intestine, fructose circulates in the bloodstream. When it passes through to the liver, liver cells rearrange fructose into glucose.

Galactose is rarely found in nature by itself but is part of the disaccharide lactose, the sugar found in milk. Absorbed like fructose, galactose is converted to glucose by the liver.

Disaccharides

Sucrose is formed from the pairing of units of glucose and fructose. We know it as table sugar. Sugarcane and sugar beets are two sources of sucrose, and it is found naturally in fruits. Because it contains fructose, sucrose is quite sweet. Sucrose has a special place in our history of food consumption and is further explored in the following section.

Maltose is created when two units of glucose are linked. It is available when cereal grains are about to germinate and the plant starch is broken down into maltose. The majority of maltose in human nutrition is created from the breakdown of starch in the small intestine. Maltose is of particular value in the production of beer and other malt beverages. When maltose ferments, alcohol is formed.

Lactose is composed of glucose and galactose. It is sometimes called milk sugar because it is the primary carbohydrate in milk.

Sugar—A Special Disaccharide

The term sugar is a word with many meanings. Sugar may refer to the simple carbohydrates (monosaccharides and disaccharides). Sucrose, the disaccharide naturally found in many fruits, is also called sugar. White table sugar refers to sucrose extracted from sugarcane and sugar beets. Sugar may also be an umbrella term used to cover numerous kcal-sweetening agents used in our food production system, although U.S. commercial law defines sugar as “sucrose.” There is a distinction between how the term sugar is used on a label versus its use by a biologist, chemist, or nutritionist. Often, blood glucose levels are called blood sugar levels. It is important that we, as health professionals, be aware that our clinical use of the term may confuse clients. Concerns about sugar focus on the following three issues: sources in the food supply, consumption levels, and health effects.

Sources in the Food Supply

Sugar in our food supply may include the following nutritive sweeteners: refined white sugar, brown sugar, dextrose, crystalline fructose, high fructose corn syrup (HFCS), glucose, corn sweeteners, lactose, concentrated fruit juice, honey, maple syrup, molasses, and reduced energy polyols or sugar alcohols (e.g., sorbitol, mannitol, xylitol)⁶ (Table 4-2). All forms of sugar are chemically similar; each provides kcal and most do not contain any other nutrients. Blackstrap molasses does contain iron, but other more nutrient-dense sources of iron are easily available. Honey, which seems less processed than other sweeteners, provides only a trace of minerals and therefore is as nonnutritious as any other sweetener.

TABLE 4-2

NUTRITIVE AND NONNUTRITIVE SWEETENERS

SWEETENER	KCAL/g	REGULATORY STATUS	OTHER NAMES	DESCRIPTION
Sucrose	4	GRAS	Granulated: coarse, regular, fine; powdered; confectioners’; brown; turbinado, Demerara; liquid: molasses	Sweetens; enhances flavor; tenderizes, allows browning, and enhances appearance in baking; adds characteristic flavor with unrefined sugar
Fructose	4	GRAS	High-fructose corn syrups: 42%, 55%, 90% fructose; crystalline fructose: 99% fructose	Sweetens; functions like sucrose in baking. Some people experience a laxative response from a load of fructose ≥20 g. May produce lower glycemic response than sucrose
Polyols-monosaccharide
Sorbitol	2.6	GRAS (label must warn about a laxative effect)	Same as chemical name	50%-70% as sweet as sucrose. Some people may experience a laxative effect from a load of sorbitol ≥50 g.
Mannitol	1.6	Permitted for use on an interim basis (label must warn about a laxative effect)	Same as chemical name	50%-70% as sweet as sucrose. Some people may experience a laxative effect from a load of mannitol ≥20 g
Xylitol	2.4	GRAS	Same as chemical name	As sweet as sucrose
Saccharin	0	Permitted for use on interim basis (label must contain cancer warning and amount of saccharin in the product)	Sweet’N Low	200%-700% sweeter than sucrose. Noncariogenic and produces no glycemic response. Synergizes the sweetening power of nutritive and nonnutritive sweeteners. Sweetening power is not reduced with heating
Aspartame	4*	Approved as a general purpose sweetener	NutraSweet, Equal	160%-220% sweeter than sucrose. Noncariogenic and produces limited glycemic response. New forms can increase its sweetening power in cooking and baking
Acesulfame K	0	Approved for use as a tabletop sweetener and as an additive in a variety of desserts, confections, and alcoholic beverages	Sunette†	200% sweeter than sucrose. Noncariogenic and produces no glycemic response. Sweetening power is not reduced with heating. Can synergize the sweetening power of other nutritive and nonnutritive sweeteners
Sucralose	0	Approved for use as a tabletop sweetener and as an additive in a variety of desserts, confections, and nonalcoholic beverages	Splenda‡	600% sweeter than sucrose. Noncariogenic and produces no glycemic response. Sweetening power is not reduced with heating

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