Eat, Drink, and Be Healthy

by Walter Willett

1 slice

  41

  12

   5

  Milk, skim

  1 cup

  32

  13

   4

  Carrots

  1/2 cup

  47

   6

   3

  * The glycemic load is calculated by multiplying the grams of carbohydrate by the glycemic index.

  Source: Foster-Powell K., Holt, S. H., and Brand-Miller, J. C. “International Tables of Glycemic Index and Glycemic-Load-Values.” American Journal of Clinical Nutrition 62 (2002): 5–56. The entire list is available for free at http://ajcn.nutrition.org/content/76/1/5.full. The University of Sydney (Australia) maintains a free searchable database of glycemic index and glycemic load values at www.glycemicindex.com.

  Fast Fact: Comparing Carbs, Fats, and Protein

  * * *

  Whole grains and other carbohydrate-rich foods low on the glycemic index are better for you than refined carbs. Compared to healthy unsaturated fats and protein, though, all carbohydrate-rich foods, regardless of the glycemic index, boost blood triglycerides and blood pressure and lower protective HDL cholesterol.10 Swapping refined grains for whole grains is a smart move. Swapping some of them for unsaturated fat or protein may be even better.

  GLYCEMIC LOAD: THE AMOUNT OF CARBOHYDRATE MATTERS TOO

  Although the glycemic index of a food is helpful information, it is only part of the story. The full effect of a food on blood glucose and insulin levels depends on both its glycemic index and the amount of carbohydrate consumed (protein and fat have small effects on blood sugar).

  Figure 16. Combined Danger of Low Fiber and High Glycemic Load. In the Nurses’ Health Study, women whose diets were low in cereal fiber and high in glycemic load were twice as likely to develop diabetes.

  For this reason, my colleagues and I developed the concept of “glycemic load.” This is the amount of carbohydrate in a food multiplied by its glycemic index. As with the glycemic index, lower numbers are better. Good choices include foods with a glycemic load of 10 or less per serving, such as beans, fiber-rich fruits and vegetables, and edamame (soybeans still in the pod) and foods made from soybeans. Moderate choices such as oatmeal, sweet potatoes, and some whole-grain crackers have glycemic loads of 11 to 19. Foods with high glycemic loads (20 and above) include sugar-sweetened soda and fruit juice, white rice, french fries and baked potatoes, and pizza.

  Glycemic load better reflects a food’s effect on your body’s biochemistry than either the amount of carbohydrate or the glycemic index alone. This is important: Some popular diet books warn against eating carrots because they were initially found to have a high glycemic index. Even if they do, carrots are mostly water, with only a small amount of carbohydrate. Finally, it’s important to consider the other nutrients in a food. For example, the glycemic load of most commercial whole wheat bread is only slightly lower than for white bread because the starch is pulverized into fine particles in both products. But the whole wheat bread is a better choice because it delivers fiber and other nutrients that are removed from the white bread. Best of all would be a coarsely ground whole-grain bread that would also have a lower glycemic index.

  While the glycemic index and glycemic load are useful tools for deciding what to eat, don’t build your whole diet around them. Some carbohydrate-rich foods deliver far more than just blood sugar. Fruits and vegetables offer fiber, vitamins, minerals, and plenty of active phytochemicals. The same is true for intact or slightly processed grains. The biggest value of the glycemic load may be for deciding among various options. When picking a snack or meal, foods with a low glycemic load are likely to be better for your heart and your insulin-making cells.

  WHAT DETERMINES A FOOD’S GLYCEMIC INDEX AND GLYCEMIC LOAD?

  One general trend you can see in the glycemic index table is that foods made from refined grains—things like white bread, bagels, and crackers—have a rapid and strong influence on blood sugar. Those that are less refined, such as coarsely ground whole-grain breads, oatmeal, and brown rice, have relatively lower glycemic index values, as do beans, vegetables, and fruits.

  Several things determine how rapidly the carbohydrates in a particular food are broken down and the resulting glucose absorbed into the bloodstream:

  • How swollen (gelatinized) the starch grains are. Starch grains swollen to the bursting point with water or heat, such as those in a boiled or baked potato, are more easily digested than the relatively unswollen starch grains found in brown rice.

  Measuring the Glycemic Index and Glycemic Load

  * * *

  Building the library of glycemic index values for foods has been a relatively slow, painstaking effort. That’s because each food must be tested on a number of volunteers, and each volunteer must be tested several times. The basic steps are the same. A healthy volunteer fasts overnight. The next morning, he or she drinks a glass of water in which 50 grams of glucose have been dissolved (or, alternately, eats 50 grams of white bread). Over the next two hours, blood samples are taken at regular intervals to measure the rise and fall of glucose. On another day, the same volunteer eats enough of the test food—cooked potato, whole-grain bread, kiwi fruit, ice cream, and so on—to consume 50 grams of carbohydrates and sits through another two hours of blood sampling. The glycemic index for that food for that individual is calculated by dividing his or her blood sugar response to the test food by the response to pure glucose or white bread. The numbers in the tables, then, represent percentages. For example, black beans have a glycemic index of 30. This means that they boost blood sugar only 30 percent as much as pure glucose.

  Because everyone processes food and responds to glucose a little differently, the glycemic index published in tables is usually the average of eight to ten volunteers.

  Once a food’s glycemic index is in hand, calculating the glycemic load is easy. It involves multiplying the glycemic index by the amount of carbohydrate actually consumed. One-quarter of a cantaloupe, then, with a glycemic index value of 65 and 5.6 grams of carbohydrate, would have a glycemic load of about 3.7 (65 percent times 5.6). A serving of mashed potato, with a glycemic index of 74 and 20 grams of carbohydrate, would have a glycemic load of 15.

  • How much the food has been processed. Grinding wheat into superfine flour dramatically increases the attack rate of digestive enzymes. Not only does flour have greater surface area than coarsely ground wheat grains, it has been stripped of the protective, hard-to-digest, fibrous outer coat that temporarily fends off enzymes from digesting the starch inside. Regular oatmeal, which is made of smashed oat grains, has a higher glycemic index than oats that are intact or sliced, usually sold as steel-cut oats. Instant oatmeal has an even higher glycemic index.

  • How much fiber it contains. As indigestible fiber passes through the intestine, it carries along partly digested food, shielding it from immediate digestion. This spreads out the release of glucose into the blood.

  • How much fat the food contains. Fats tend to increase the time it takes for food to leave the stomach and enter the intestine. So a food that contains fat may temper the rise in blood sugar.

  • What else is consumed. Something acidic, like vinegar or lemon juice, can slow the conversion of starch to sugar, as do oils and fats. That means the glycemic index of a whole meal is influenced by the combination of foods that are eaten together. That said, eating a low glycemic food instead of a high glycemic food will lower the impact of the overall meal on blood sugar.

  INTACT GRAINS, WHOLE GRAINS, AND REFINED GRAINS

  Various terms are used to describe grain. Here are the key terms that I use. Intact grains are those that have barely been processed, if they’ve been processed at all. They look much the same as they did when they were harvested. Whole grains include intact grains and also grains that have been processed—ground, chopped, steamed, or the like—but nothing has been removed. (If you aren’t familiar with intact and whole grains, check out the “Directory of Who
le or Intact Grains” on page 272.)

  Webster’s defines the word “refined” as “free from impurities.” That certainly applies to refined grains. Unfortunately, the “impurities” removed by refining include fiber, vitamins, minerals, and a variety of other beneficial micronutrients and phytochemicals.

  Let’s look at wheat as an example. Wheat is a gigantic relative of the grass that grows in yards and parks all across America. The hollow stem supports a seed head that’s tightly packed with many individual grains. Our ancestors often used these grains as they came from the plant, and many people still use these “wheat berries” with meals or in breakfast porridges. Today, though, most wheat is processed and refined. The milling process first cracks the wheat grains. The starchy, carbohydrate-rich center, called endosperm, is separated from both the dark, fibrous bran and the wheat embryo, called the wheat germ. The endosperm is then pulverized with a series of rollers to make white, powdery flour. If the wheat grain is milled into fine flour without removing the bran and germ, this is technically a whole-grain product, since all the original parts are still present. But it is no longer an intact whole grain.

  At each stage of milling, something is lost. Removing the germ pulls out unsaturated fats and fat-soluble vitamins. Whacking away the branny outer layer removes fiber, magnesium, and more vitamins. By the time wheat grains have been turned into white flour, the final product is a pale shadow of the original, literally and nutritionally (see Figure 17 above).

  Figure 17. Grain Drain. Important nutrients disappear when whole grains are refined. As this baker’s dozen shows, the losses can be dramatic. Refined white flour, for example, has barely 5 percent of the vitamin E of whole wheat flour.

  If intact grains are so healthy, why did we stop eating them and shift to highly refined grains? It’s partly a function of perception. Once it became possible to refine wheat, white flour was marketed as being purer than whole-grain flour. At first, white flour was a novelty for the upper classes. The bread and pastries it made were lighter and airier than their whole-grain cousins. In time, buying white flour became a symbol of moving up in the world. The shift was also driven by the reality of storage: white flour, with almost none of the healthy oils found in whole-grain flour, keeps longer. Whole-grain flours must be used more quickly and/or refrigerated.

  For the past four decades, my colleagues and I have been studying the health effects of refined and whole-grain foods with the dedicated help of more than 200,000 women and men participating in the Nurses’ Health Study, the Nurses’ Health Study II, and the Health Professionals Follow-Up Study. The result of this work is compelling: eating whole grains and foods made from them is clearly better for sustained good health and offers more protection against a variety of chronic diseases than a diet high in refined carbohydrates or potatoes. Other research around the world points to the same conclusion.

  WHOLE GRAINS PROTECT AGAINST DIABETES

  Whole Grains and Weight Control

  * * *

  The slower, gentler effects of whole grains on blood sugar and insulin, and the feeling of fullness after eating provided by greater fiber intake, translates into better weight control. My colleagues and I looked at the effects of whole grains in three long-term cohorts of nearly 173,000 men and women. Those who ate several servings of whole grains a day were less likely to have gained weight, or gained less weight, over twenty-four years’ follow-up than those who rarely ate whole grains.11 By helping you feel full longer after a meal or snack, whole grains can help you eat less.

  Roller-coaster blood sugar levels and the loss of fiber-containing bran can affect more than just how fast you get hungry after a meal or snack. They can also influence the development of diabetes.

  My colleagues and I studied all participants in the Nurses’ Health Study and the Health Professionals Follow-Up Study who were free of diabetes when we first collected data on diet in the 1980s. During twenty-plus years of follow-up, more than 15,000 of the participants developed type 2 diabetes. Those whose diets scored highest on the glycemic index were 33 percent more likely to have developed diabetes than those with low glycemic index diets.12 Participants with high glycemic index diets and low-fiber diets were 60 percent more likely to have developed type 2 diabetes. In these studies, eating high-fiber cold breakfast cereal seemed to help reduce the risk of developing diabetes, while consuming soft drinks, white bread, white rice, french fries, and cooked potatoes were all associated with increased risk of diabetes.

  Developing healthy dietary habits as early as possible, ideally during childhood, is best for long-term health. The good news about preventing diabetes is that no matter how old you are, if you have managed to escape diabetes so far, adopting a healthy diet and physical activity program today will lower your risk starting tomorrow. That’s a terrific immediate return on investment. Other benefits, such as reduced risks of heart disease and cancer, will follow but some may take years to show up.

  WHOLE GRAINS MEAN LESS HEART DISEASE

  Refined grains pose other problems in addition to diabetes. They are also linked to heart disease and stroke.

  In the Nurses’ Health Study, women who reported eating the most intact grain foods, an average of 2.5 servings a day, were 30 percent less likely to develop heart disease than women eating the fewest, about 1 serving a week.13 Most of their whole grains came from whole-grain breakfast cereals, brown rice, and whole-grain bread. We estimated that eating a bowl of cold breakfast cereal that supplies about 5 grams of fiber cuts the chance of developing heart disease by about one-third compared with a fiber-free breakfast. The apparent benefit was larger in overweight women than it was in lean women. These benefits have also been seen consistently in other long-term studies of heart disease. Systematic reviews and meta-analyses of long-term cohort studies have linked high glycemic index and high glycemic load diets to increased risk of heart attack, stroke, and heart-related deaths.14

  WHOLE GRAINS IMPROVE GI HEALTH TOO

  Constipation is the number one gastrointestinal complaint in the United States. It affects more than 60 million Americans, accounting for more than 4 million physician visits and three-quarters of a million trips to emergency departments a year.15 We spend more than $1 billion a year on over-the-counter laxatives. But there’s a dietary remedy to this problem: foods rich in fiber. By keeping the stool soft and bulky, the fiber in intact grains helps prevent this troubling problem.

  Two other common GI problems are diverticulosis, the development of tiny, easily irritated pouches inside the colon, and diverticulitis, the often painful inflammation of these pouches. Fiber from grains, as well as from fruits and vegetables, adds bulk to the stool and softens it. Together, these actions decrease pressure inside the intestinal tract and help prevent diverticular disease.

  UNCERTAIN EFFECTS ON CANCER

  Although a number of early studies suggested that higher consumption of whole grains or fiber reduced the odds of developing mouth, stomach, colon, gallbladder, and ovarian cancer, later and larger studies haven’t consistently borne this out. Analyses from the Nurses’ Health Study, the Health Professionals Follow-Up Study, and a compilation of large cohort studies from around the world showed that men and women with the highest fiber intake did not have lower risks of colorectal cancer.16

  The timing of fiber intake, however, may be important. Among the middle-aged participants of the Nurses’ Health Study, we saw no relation between fiber intake and risk of breast cancer. In the Nurses’ Health Study II, which was established to look at diet earlier in life, we found that higher fiber intake during adolescence predicted a lower risk of breast cancer later in life.17

  Even if whole-grain, high-fiber foods have no effect on cancer, their impact on heart disease and diabetes is reason enough to eat grains in this form instead of their stripped-down counterparts.

  WHAT MAKES INTACT AND WHOLE GRAINS BETTER?

  It may be almost impossible to isolate the ingredient or ingredients in whole grains that red
uce the risks of heart disease and diabetes. However, a few contenders have been identified. The fiber in whole grains delays absorption of glucose into the bloodstream and eases the workload for insulin-making cells in the pancreas. Fiber helps lower cholesterol levels in the blood. It may also rev up some of the body’s natural anticoagulants and help prevent the formation of small blood clots that trigger heart attacks or strokes. Antioxidants like vitamin E in whole grains prevent cholesterol-containing low-density lipids from reacting with oxygen, a key early step toward the formation of cholesterol-clogged arteries. Phytoestrogens, or plant estrogens, may protect against some cancers. The bran layer of many grains contains essential minerals such as magnesium, selenium, copper, and manganese that may be important in reducing the risk of heart disease and diabetes.

  SEPARATING THE WHEAT FROM THE CHAFF

  What exactly is a whole-grain food? This shouldn’t be a trick question, but it is. Part of the problem is our lack of knowledge about the foods we eat. The other is that food makers, eager to promote any health benefits that might sell their products, jumped on the fiber/whole-grain bandwagon and haven’t gotten off. Stroll the aisles of your favorite grocery store and you’ll see what I mean. General Mills Total is a whole-grain breakfast cereal; Quaker Puffed Wheat isn’t. Nabisco Triscuit and Wheat Thins are whole-grain crackers, while Keebler Toasteds Harvest Wheat crackers are mostly refined wheat.

  Some choices are easy. Brown rice is whole grain, white rice isn’t. Most of the time, though, it takes a savvy shopper to separate the whole grain from the refined. You have to read food labels with the discriminating eye of a food critic, alert for subtle nuances that spell the difference between whole grain and refined grain. If the label says “made with wheat flour,” it may be a whole-grain product—or it may just be an advertising gimmick and made with entirely refined wheat flour. The silkiest, most refined white cake flour is “made with wheat flour.” True whole-grain products should list as the main ingredient whole wheat, whole oats, whole rye, or some other whole grain. To be 100 percent whole grain, no other type of grain should be on the list. The FDA isn’t helpful here: a product can be labeled as whole grain if 51 percent of the grain is whole grain; the rest can be refined starch.