Having one-third of a 12-inch pepperoni pizza for dinner on the run? The cheese and crust amount to about 84 grams of carbohydrates, or the equivalent of wolfing down 21 teaspoons of sugar. The glycemic index of that meal is 60 (medium). The glycemic load is 51 (high).
Willett also counsels that dairy products—which supply concentrated calories and saturated fat—are not the best way to get calcium and that the recommended daily intake of 1,200 milligrams daily for adults over 50 appears to be more than what’s needed. His advice: Eat calcium-bearing vegetables, including leafy greens, take calcium supplements if you’re a woman, and exercise. “The evidence for physical activity being protective against fractures is huge,” he says.
And he defends eggs. Although cholesterol fears have caused American per capita egg consumption to drop from 400 to 250 per year, “no research has ever shown that people who eat more eggs have more heart attacks than people who eat fewer eggs,” Willett says. A 2001 Kansas State University study identified a type of lecithin called phosphatidylcholine in eggs that interferes with cholesterol absorption, which may explain why many studies have found no association between egg intake and blood cholesterol level. If the breakfast menu option is a white-flour bagel or an egg fried in vegetable oil, says Willett, “the egg is the better choice.”
Perhaps the most comprehensive studies Willett has assembled compare the health consequences of eating saturated versus unsaturated fat. The term saturated means that every available site along each fat molecule’s carbon chain is filled with a hydrogen atom; such fats—including butter and animal fat—are solids at room temperature. There are two types of unsaturated fats: monounsaturated fats such as olive oil, which are missing one pair of hydrogen atoms, and polyunsaturated fats such as soy, corn, and canola oils, which lack more than one pair. Both sorts are liquid at room temperature.
Some researchers have questioned whether saturated fat is dangerous. In his book, The Cholesterol Myths: Exposing the Fallacy That Saturated Fat and Cholesterol Cause Heart Disease, Swedish physician Uffe Ravnskov asserts that as of 1998, 27 studies on diet and heart disease had been published regarding 34 groups of patients; in 30 of those groups investigators found no difference in animal fat consumption between those who had heart disease and those who did not. “Anyone who reads the literature in this field with an open mind soon discovers that the emperor has no clothes,” Ravnskov writes.
Willett turns to his Nurses’ Health mega-study for the definitive word. “The amounts of specific fats did make a difference,” he says. “Women who ate more unsaturated fat instead of saturated fat had fewer heart problems.” Willett calculated that replacing 5 percent of saturated fat calories with unsaturated would cut the risk of heart attack or death from heart disease by 40 percent. Other studies—notably the French Lyon Diet Heart study, begun in 1988—show a similar correlation.
A healthy diet plan is worthless if people won’t stick to it, and Susan Roberts, director of the energy metabolism laboratory at Tufts University, contends that Willett’s regimen is too severe. “Most people would say his recommendations are healthy but that other, less difficult diets are healthy too,” she says.
Difficult is in the palate of the eater. The last half of Willett’s book aims to dispel any taint of Calvinism with recipes that verge on the sybaritic, including pork tenderloin with pistachio-gremolata crust, chicken enchilada casserole, and grilled salmon steaks with papaya-mint salsa. On the other hand, some resolve might be required to soldier through a few of the other dishes listed there, including hearty oat–wheat berry bread or the onion-crusted tofu-steak sandwich. But most people, Willett believes, can summon the willpower to substitute whole-wheat flour for white and plant oils for shortening or lard, and eat less sugar overall. “I think what I suggest is not severely restrictive, because it can be achieved mainly by substitution,” rather than slavishly following recipes, Willett says. In any case, “it does not mean you cannot eat any of those foods but rather that they should be de-emphasized.”
So take heart. Even Willett has a little chocolate now and then.
| GOOD CARBS/BAD CARBS The glycemic index (GI) is a way of measuring how quickly the carbohydrate in a given food raises the level of blood sugar. So eating a low-GI food causes a slow, mild rise, while the same quantity of carbohydrate in a high-GI food will trigger a faster, bigger rise. A GI of 55 or less is considered low, 56 to 69 is medium, and 70 or more is high. But the GI is of limited use in the real world of pears, pork, and pudding because it ignores how much of that food a person eats. A few years ago, Walter Willett pioneered the concept of the glycemic load (GL), a measurement that factors in the quantity of carbohydrates eaten in a single serving of a particular food. The carbohydrates in parsnips, for example, are quickly converted to glucose, so parsnips have a rather high index of 97, plus or minus 19 (the numbers are sometimes imprecise because they are based on feeding foods to test subjects and monitoring their blood-sugar response, which can vary for many reasons). But parsnips have a GL of just 12, because a single 80-gram serving contains a relatively small amount of carbohydrate. A GL of 10 or less is considered low, 11 to 19 is medium, and 20 or more is high. Consistently eating low-GL foods evens out blood-sugar peaks and valleys, which Willett says helps keep appetite and weight under control. Eating low-GL foods also reduces the risk of developing type 2 diabetes. When Willett says “good carbs,” he is essentially referring to fiber-rich, low-GL foods. Generally, whole grains have lower glycemic loads than refined grains. For example, a 150-gram serving of brown rice has a GL of 18, while the same serving of quick-cooking white rice has a GL of 29. Although the photographs in this story tally the “sugar equivalence” of the carbohydrates in various American foods, the glycemic index and glycemic load of each of these foods needs to be considered as well. The glycemic numbers accompanying the photographs in this article are from Janette Brand-Miller of the University of Sydney, based on a table published in the July 2002 issue of The American Journal of Clinical Nutrition. An adaptation of that table can be seen at diabetes.about.com/library/mendosagi/ngilists.htm. —B. L. |
