Part One R Nutrition and Diet
1 R Carbohydrates: Sugar, Starch and Dietary Fiber Carbohydrates often get a bad rap they make you fat, they cause diabetes, they trigger hyperactivity in children. However, contrary to the claims of many fad diets, carbohydrate-containing foods are an important component of a healthy diet and do not cause health problems if eaten according to proper guidelines. Carbohydrates provide about half of all the energy used by your muscles, nerves and other body tissues. And carbohydrate is your brain s preferred fuel source the brain relies on a steady supply of carbohydrate to function properly. In fact, carbohydrate-rich foods should be the major source of energy in your daily diet. And if you choose your carbohydrates wisely, these foods also supply a fair share of fiber, vitamins, minerals and protective plant chemicals. What Is Carbohydrate? 2 Carbohydrate is composed of carbon, hydrogen and oxygen and is found almost exclusively in plant foods. Plants make the carbohydrate we eat from carbon dioxide, water and the sun s energy. Fruit, vegetables, whole grains, legumes and nuts are all sources of carbohydrate. The only animal foods with carbohydrate are dairy products, which contain a naturally occurring sugar called lactose. The carbohydrate family includes simple sugars, starches and dietary fiber.
Carbohydrates: Sugar, Starch and Dietary Fiber 3 Simple sugars are classified as either monosaccharides ( mono meaning one and saccharide meaning sugar) or disaccharides (two sugars). Monosaccharides are the simplest form of carbohydrate because they consist of a single sugar molecule. The three monosaccharides important to nutrition are glucose (also called dextrose and blood sugar), fructose (found in fruit, honey and corn syrup) and galactose. Galactose rarely occurs by itself in foods; instead, it attaches to another sugar unit to form the disaccharide lactose. Disaccharides are pairs of monosaccharides linked together. Maltose (malt sugar), sucrose (table sugar) and lactose (milk sugar) are disaccharides we consume every day. Starches are more complex arrangements of carbohydrate. Starches in foods are long chains of hundreds or thousands of glucose units linked together. These giant molecules are stacked side by side in a grain of rice, a slice of bread or a flake of breakfast cereal. Other starchy foods are potatoes, wheat, rye, oats, corn and legumes (including chickpeas, kidney beans and lentils). Dietary fibers are the structural parts of vegetables, fruit, grains and legumes. Pectins, lignans, cellulose, gums and mucilages are all different forms of fiber found in these foods. Although our digestive enzymes are not able to break down the chemical bonds that link the building blocks of fiber, bacteria in our colon can digest some of these fibers. Dietary fiber is made up of two types of fiber: soluble and insoluble.both are present in varying proportions in the different plant foods; some foods may be rich in one or the other. Soluble fibers dissolve in water. Once consumed, they form a gel in the stomach and slow the rate of digestion and absorption. Dried peas, beans and lentils, oats, barley, psyllium husks, apples and citrus fruits are good sources of soluble fiber. Diets high in soluble fiber have been shown to stabilize blood sugar and reduce the need for insulin in some people with diabetes. And plenty of evidence supports the cholesterol-lowering effect of oat bran and psyllium. s like wheat bran, whole grains and certain vegetables contain mainly insoluble fibers. These fibers have a significant capacity for retaining water and act to increase stool bulk and promote regularity. By reducing constipation, a diet high in fiber may prevent a condition called diverticulosis (see page 275). Since high-fiber diets are usually low in fat and calories, they also may help you achieve and maintain a healthy weight. To reap its health benefits, Canadians should be getting 25 to 35 grams of fiber in their diets each day. Here s a list of fiber-rich foods: Legumes and Nuts Beans and tomato sauce, canned, 1 cup (250 ml) Black beans, 1 cup (250 ml), cooked Fiber (grams) 20.7 g 13.0 g
4 Part One Nutrition and Diet Chickpeas, 1 cup (250 ml), cooked Kidney beans, 1 cup (250 ml), cooked Lentils, 1 cup (250 ml), cooked Almonds, 1/2 cup (125 ml) Peanuts, dry roasted, 1/2 cup (125 ml) Fiber (grams) 6.1 g 6.7 g 9.0 g 8.2 g 6.9 g Cereals 100% bran cereal, 1/2 cup (125 ml) 10.0 g Bran Flakes, 3/4 cup (175 ml) 6.3 g Grape Nuts, 1/2 cup (125 ml) 6.0 g Kellogg s All Bran Buds, 1/3 cup (75 ml) 13.0 g Quaker Corn Bran, 1 cup (250 ml) 6.3 g Oat Bran, 1 cup (250 ml), cooked 4.5 g Oatmeal, 1 cup (250 ml), cooked 3.6 g Red River Cereal, 1 cup (250 ml), cooked 4.8 g Shreddies, 3/4 cup (175 ml) 4.4 g Bread and Other Grain s Pita pocket, whole wheat, 1 Whole wheat bread, 100%, 2 slices Spaghetti, whole wheat, 1 cup (250 ml), cooked Rice, brown, 1 cup (250 ml), cooked Flaxseed, ground, 2 tbsp (30 ml) Wheat bran, 2 tbsp (30 ml) Fruits Apple, 1 medium with skin Apricots, dried, 1/4 cup (60 ml) Banana, 1 medium Blueberries, 1/2 cup (125 ml) Figs, 5 dried Orange, 1 medium Pear, 1 medium with skin Prunes, 3 dried Raisins, seedless, 1/2 cup (125 ml) Strawberries, 1 cup (250 ml) Vegetables Broccoli, 1/2 cup (125 ml) Brussels sprouts, 1/2 cup (125 ml) Carrots, 1/2 cup (125 ml) 4.8 g 4.0 g 4.8 g 3.1 g 4.5 g 2.4 g 2.6 g 2.6 g 1.9 g 2.0 g 8.5 g 2.4 g 5.1 g 3.0 g 2.8 g 3.8 g 2.0 g 2.6 g 2.2 g
Carbohydrates: Sugar, Starch and Dietary Fiber 5 Corn niblets, 1/2 cup (125 ml) Green peas, 1/2 cup (125 ml) Lima beans, 1/2 cup (125 ml) Potato, 1 medium baked with skin Sweet potato, 1/2 cup (125 ml), mashed Fiber (grams) 2.3 g 3.7 g 3.8 g 5.0 g 3.9 g Nutrient Values of Some Common s, Health Canada, Ottawa, 1999. Carbohydrate and Digestion The process of carbohydrate digestion begins in your mouth, where an enzyme in saliva starts to break down starch once you have eaten a carbohydrate meal or snack. The food then makes its way into your small intestine, where digestive enzymes are released to break down starches into smaller units. Finally, vital enzymes on the surface of your intestinal cells dismantle disaccharides into their monosaccharide building blocks. (Inflammatory diseases, certain medications, hereditary factors and age can predispose us to deficiencies in some of these enzymes, most commonly, lactase deficiency. People who don t produce enough lactase cannot break down the milk-sugar lactose into its two components, glucose and galactose. The result is cramping, bloating, gas and diarrhea. See page 407 for more on lactose intolerance.) Once digested, the three monosaccharides glucose, fructose and galactose enter the bloodstream and make their way to the liver. Here, fructose and galactose are converted to glucose. Some glucose is used immediately for energy, while some is stored as glycogen, the body s storage form of carbohydrate (glucose), which the liver breaks down and releases as glucose according to your body s need for energy. When your blood-sugar level falls because you haven t eaten for a while, glucose is released so body cells can use it to fuel metabolic reactions. But your liver is able to store only about one-third of your body s glucose. The rest is housed in your muscles as glycogen. During exercise, your body burns glycogen in order to keep muscles contracting. This is why low-carbohydrate diets can make exercise difficult: your muscles feel tired and you fatigue much sooner. Carbohydrate and the Glycemic Index By now it s apparent how important carbohydrate is for energy. All carbohydrate-rich foods ultimately end up as glucose in your bloodstream, where it s used to fuel your body s metabolic machinery. But the speed at which that glucose enters your bloodstream may affect your hunger, your weight, even your long-term health.
6 Part One Nutrition and Diet Carbohydrates do not raise your blood sugar all in the same way. Some carbohydrate-rich foods are digested and absorbed into your bloodstream quickly, while others are broken down and converted to blood glucose more slowly. What effect does this have on your feeling of energy? Let s say you eat two slices of toast for breakfast. Bread (both white and whole-wheat) is digested relatively quickly, causing your blood glucose to rise quickly. This rapid rise in blood glucose triggers your pancreas to release an excessive amount of insulin, the hormone that regulates blood sugar, causing your blood-glucose level to drop to a very low level. The result is that you ll feel sluggish and tired, not to mention hungry, not long after eating the toast. Moreover, studies suggest that regularly eating foods that cause high blood insulin levels may increase the risk of heart disease and cancer. On the other hand, a bowl of high-fiber breakfast cereal with low-fat milk is digested and absorbed more slowly, causing a gradual rise in blood glucose. Because this meal does not result in a fast blood-sugar response, you don t get a surge of insulin. As a result, your blood-sugar level won t plummet. Instead you will experience a smooth, steady blood-sugar level, leading to more consistent energy levels. The rate at which a food causes your blood sugar to rise can be measured and assigned a value. This measure is referred to as the food s glycemic index value. The glycemic index (GI) is a ranking from 0 to 100. The number indicates whether a food raises your blood glucose rapidly, moderately or slowly. s that are digested quickly and cause your blood sugar to rise rapidly have high glycemic index values. s that are digested slowly leading to a gradual rise in blood sugar are assigned low glycemic index values. All foods are compared to pure glucose, which is given a value of 100 (fast acting). The glycemic index is used, and being studied, in athletics. After heavy exercise that depletes muscle carbohydrate stores (what muscles use for fuel during exercise), consuming a high glycemic index food such as a bagel or sugary drink is best since it will be more rapidly digested and converted to blood glucose. That means muscles will recover and rebuild their energy stores faster. A low glycemic index food such as yogurt is best for a preworkout snack since it will take longer to be converted to blood sugar. That means that when you start to exercise, your blood-glucose levels are starting to increase, giving your muscles energy for the workout. To help prevent large increases in blood sugar, practice the following: Choose low GI foods for your meals. Avoid eating high GI foods as snacks as they can trigger low blood sugar; choose low GI foods instead. Combine a high GI food with a low GI food to result in a meal with a medium GI value.
Carbohydrates: Sugar, Starch and Dietary Fiber 7 Here s a list of foods ranked by their GI value; < 55 = low GI; 55 70 = medium GI; > 70 = high GI. Use this table to plan your meals. Bread and Crackers Baguette, French 95 Kaiser roll 73 Melba toast 70 Pita bread, whole-wheat 57 Pumpernickel, whole-grain 51 Rice cakes 82 Rye bread 65 Soda crackers 74 Sourdough bread 52 Stoned Wheat Thins 67 White bread 70 Whole-wheat bread 69 Breakfast Cereals All Bran, Kellogg s 51 All Bran Buds with Psyllium, Kellogg s 45 Bran Flakes 74 Corn Bran, Quaker 75 Corn Flakes 84 Oat Bran 50 Oatmeal 49 Raisin Bran 73 Shredded Wheat, spoon size 58 Special K 54 Cookies, Cakes and Muffins Angelfood cake 67 Arrowroot 69 Banana bread 47 Blueberry muffin 59 Graham crackers 74 Oat bran muffin 60 Oatmeal cookies 55 Social Tea biscuits 55 Sponge cake 46 GI Value
8 Part One Nutrition and Diet GI Value Pasta, Grains and Potato Barley 25 Bulgur 48 Corn, sweet 55 Couscous 65 Fettuccine, egg 32 Potato, french fries 75 Potato, new, unpeeled, boiled 62 Potato, instant, mashed 86 Potato, red-skinned, mashed 91 Potato, red-skinned, boiled 88 Potato, white-skinned, baked 85 Rice, basmati 58 Rice, brown 55 Rice, converted, Uncle Ben s 44 Rice, instant 87 Rice, long-grain, white 56 Rice, short-grain 72 Spaghetti, whole-wheat 37 Spaghetti, white 41 Sweet potato, mashed 54 Legumes Baked beans 48 Black beans 31 Black bean soup 64 Chickpeas, canned 42 Kidney beans 27 Lentils 30 Lentil soup, canned 34 Soy beans 18 Split pea soup 66 Fruit Apple 38 Apricot, dried 31 Banana 55 Cantaloupe 65 Cherries 22 Dates, dried 103
Carbohydrates: Sugar, Starch and Dietary Fiber 9 GI Value Grapefruit 25 Grapes 46 Mango 55 Orange 44 Peach, canned 30 Pear 38 Raisins 64 Watermelon 72 Dairy Products and Alternatives Milk, skim 32 Milk, whole 27 Milk, chocolate 34 Ice cream, low-fat 50 Soy beverage 31 Yogurt, flavored, low-fat 33 Snack s Corn chips 72 Peanuts 14 Popcorn 55 Potato chips 54 Pretzels 83 Sports Bar, PowerBar, chocolate 58 Sugars Fructose (fruit sugar) 23 Glucose 100 Honey 58 Lactose (milk sugar) 46 Sucrose (table sugar) 65 Foster-Powell, K. and J. Brand Miller. International tables of glycemic index, American Journal of Clinical Nutrition 1995; 62:871S-893S. Carbohydrate and Weight Control After reading about the importance of carbohydrate, you might be wondering why some diet books shun them. Books like Dr.Atkins Protein Revolution, Sugar Busters and Protein Power Plan recommend eliminating or drastically reducing carbohydrates from your diet for a period in order to help you lose weight. Many of these diets
10 Part One Nutrition and Diet claim that carbohydrates make you fat. However, carbohydrate-rich foods will make you gain weight only if you re eating a lot of them, or if you re slathering them with high-fat spreads or sauces. It is true, however, that many people today overeat carbohydrates highcarbohydrate foods are often fast, portable and fat free. Yet, although they contain very little fat, dense bagels, fat-free muffins, baked pretzels and bowls of pasta all add calories to your diet. Often, fat-reduced foods are not much lower in calories than the original version. Did you know that a large bagel is the equivalent of five slices of bread? Or that 20 pretzel sticks are equivalent to two slices? Even that restaurant portion of pasta with tomato sauce is probably worth at least four slices of bread (not to mention the bread you might eat with it!). And here s a shocker: one slice of pizza from the street-corner shop can have as much carbohydrate as seven slices of bread. When it comes to weight control, portion size is what counts. Carbohydrate and Diabetes It is a common misconception that consuming too much sugar will cause diabetes. As you ll read on page 263, diabetes is a disease caused by genetic and lifestyle factors. It occurs when the body does not produce enough insulin, or does not use it properly. As a result, rather than entering blood cells, glucose builds up in the bloodstream and is excreted in the urine, thus not providing body cells with their main source of fuel. People with diabetes must carefully manage their carbohydrate intake. Meals need to be regularly scheduled and contain measured portions of carbohydrate foods. However, people with diabetes are allowed to eat a little bit of sugar. Carbohydrate and Dental Caries Here s where sugar is a culprit. In the mouth, the enzyme amylase begins breaking down starch into smaller units of starch and the disaccharide maltose. Bacteria in the mouth then ferment these carbohydrates and, in the process, produce an acid that erodes tooth enamel. The longer carbohydrate foods stay in the mouth, the greater the chance that cavities will form. Sticky foods like candy adhere to the teeth and will keep acid-yielding bacteria in action longer. Snacking on carbohydrate-rich foods regularly throughout the day will keep the bacteria working, too.
Carbohydrates: Sugar, Starch and Dietary Fiber 11 Eating nonsugary foods can help remove carbohydrate from the surface of your teeth. This is why, as you may have heard, eating cheese can help prevent cavities. Rinsing your mouth and brushing your teeth after eating are important strategies to help prevent dental caries. How Much Carbohydrate Should You Eat? Here s what you should be striving for each day: 1. At least 55 percent of your daily calories should come from carbohydratecontaining foods. This means that foods like legumes, grains, vegetables and fruit should take up from two-thirds to three-quarters of your plate. 2. As often as possible, choose whole grains: starchy foods that have not been refined and retain important minerals, vitamins, antioxidants and fiber. (You ll read more about whole grains in Chapter 5.) Choose 100 percent whole-wheat bread, whole rye or pumpernickel bread, brown rice, whole-wheat pasta and breakfast cereals made from whole grains. 3. Limit your intake of sugary foods like candy, chocolate, soda pop, fruit drinks, desserts and other sweets. I advise my clients to treat themselves once a week. 4. Strive to include 25 to 35 grams of dietary fiber in your daily diet. If you, like the average Canadian, are getting only about half this amount, gradually work more fiber into your diet. The list of fiber-containing foods on page 3 will give you some ideas. 5. Remember that fiber needs fluid to work. Be sure to consume at least eight glasses of water each day. And always have a glass of water with a high-fiber meal or snack.