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NUTRITION Cracks in the PyramidStudy Finds Little Benefit in Following Food Pyramid Guidelines If you are asked for good advice, you want to make sure your advice works before you hand it out. If you are the federal government and want to give out good advice on what makes for a healthy diet, you convene a panel of experts in medicine, public health, and nutrition to tell you what works. Since 1980, the federal government has been issuing that expert advice as the Dietary Guidelines for Americans. In 1992, the guidelines were morphed into the Food Pyramid, a simple graphic display of the officially approved healthy diet that became a fixture on the side panels of cereal boxes. Unfortunately no one checked to see how much the guidelines, which were revised in 1995, would actually improve health. This week, a team of HSPH epidemiologists came up with the answer—not enough. In two separate studies published in the November American Journal of Clinical Nutrition, the HSPH researchers led by Walter Willett, the Frederick Stare professor of epidemiology and nutrition, found that closely following the 1995 Dietary Guidelines yielded surprisingly little benefit.
HSPH researchers say the Food Pyramid needs a redesign because not all fats are bad and not all carbohydrates are good. The pyramid also has too much dairy, sugar, red meat, and potatoes, they say. —Christina Roache, HSPH, and the U.S. Depts. of Agriculture and of Health and Human Services The Missing FoundationThe researchers analyzed data from 67,000 women in the Nurses' Health Study and 39,000 men from the Health Professionals Follow-up Study. The USDA's Healthy Eating Index, a "report card" of how well Americans' diets conform to the dietary guidelines, was used to grade the diets of these men and women. The researchers then looked to see who was diagnosed with major diet-related chronic diseases such as heart attack, stroke, and cancer over a 10-year period. They found that higher scores (implying close adherence to the guidelines) were related to only 11 percent reduction in men and 3 percent reduction in women of major chronic diseases. A moderate reduction in cardiovascular disease risk was observed in men, but the findings were weaker for women. Further, there was no discernible reduction in risk of cancer for either group.The researchers say this evidence suggests that the 1995 pyramid and the dietary guidelines on which it stands are out of whack with the latest scientific findings on diet and long-term health. The guidelines were just revised for 2000 by the Department of Agriculture and the Department of Health and Human Services, but the HSPH researchers say they still heavily reflect the outdated assumptions of the 1995 version they put to the test. Besides Willett, who is on sabbatical, collaborators on both papers included Meir Stampfer, the new chair of the HSPH Department of Epidemiology; Diane Feskanich, HMS instructor in medicine; and lead author Marjorie McCullough, an HSPH graduate student who conducted the research as part of her doctoral thesis. McCullough is now with the American Cancer Society in Atlanta. Both studies were done by reanalyzing data on eating patterns drawn from the two long-term epidemiological studies, the female Nurses' Health Study which began in 1976, and the male Health Professionals Follow-up Study, which began enrolling dentists, veterinarians, pharmacists, optom-etrists, and osteopathic physicians in 1986. For the men, the original intake questionnaire contained a long section on eating habits and that information was updated in 1990. For the women, the study was based on an exhaustive questionnaire on their eating habits in 1984, updated in 1986 and 1990. Excluding unrealistic responses and those who had already been diagnosed with a major disease, the researchers ended up with finely detailed dietary information from 67,272 women and 38,622 men. The studies have extensive "endpoint data"—the onset of cardiovascular disease, cancer, or death from non-traumatic causes—on the men through 1994 and for the women through 1996. It was this mass of long-term data that allowed the epidemiologists to pull off what would have been an impossible real-time experiment. They were able to grade the diets of individuals during the mid-'80s through the mid-'90s using dietary guidelines that were not issued until 1995. They were able to adjust for smoking and other known risk factors, and look to see if higher scores were associated with lower disease risk. Eating according to the pyramid did bestow some protective benefits for cardiovascular disease, especially in men, said McCullough. As a whole, however, the benefits of following the 1995 dietary guidelines were not very evident. Said McCullough, "This does not mean that diet is not important in chronic disease. We know it's very important. This suggests that the diet guidelines have to be improved and made more specific. Dietary guidelines are an evolving entity." Dismantling the PyramidDietary evolution, at least the official version, is a strange mix of science, policy, and politics. The 1995 food pyramid depicted a recommended number of daily servings from each of the five major food groups of grains, vegetables, fruit, milk products, and meat. The "healthiest" foods, including all carbohydrates, were the wide base with the greatest number of recommended servings; the "least healthy" foods, especially fats, were the narrow top with the greatest cautions. What has changed since 1995 is a new understanding of the role of different fats and different carbohydrates in human nutrition, according to Stampfer. All fats are no longer considered bad; all carbohydrates are not created equal.Besides his work on both these papers, Stampfer has another perspective on the Food Pyramid. He also served on the joint USDA and Health and Human Services advisory panel of 11 experts to update the 1995 dietary guidelines for 2000. Said Stampfer, "The amazing thing is that they had made this pyramid and made these guidelines and nobody tested to see whether the people who followed these guidelines were any healthier than people who didn't. It was never tested. It seems incredible. They tested it for public perception, public understanding, how many people had heard of the pyramid, what does the pyramid mean, but they never tested to see whether if you followed the pyramid you were doing yourself a favor or not. These papers really represent the first formal test." According to these new studies, how effective is the dietary approach embodied in the pyramid? "It's not very good," Stampfer said. "It's not too bad for you and that's a plus, but we could do, oh, so much better." Yet the revised 2000 guidelines that he worked on are not much better. Stampfer said the panel engaged in a kind of scientific self-censorship, for fear of going too far in its revisions and having the two department secretaries, who are political appointees, reject them entirely. That's why the dietary guidelines for the year 2000 remain unsatisfactory, Stampfer said. "There's too much emphasis on carbohydrates; too much emphasis on reduction of total fat as opposed to distinguishing the type of fat. What we really need to do is eliminate transfat [hydrogenated vegetable oil] or come close to eliminating it. We need to reduce saturated fat. But there's no need to reduce unsaturated fat and in some instances, we need to increase our intake of unsaturated fat. "There's too much emphasis on dairy products. There's not enough distinction of quality of carbohydrate, that is, the kinds of food that very rapidly raise blood sugar—things like white bread, potatoes, and more refined carbohydrates—as opposed to carbohydrates—like whole grains—that are less prone to raise blood sugar. Some carbohydrates raise blood sugar faster than others so when that happens you have a rapid rise in glucose, a rapid rise in insulin, a rise in trishtmlglycerides, and lower HDL—it's bad for you, basically. Whereas carbohydrates that take longer to digest and metabolize don't have those rapid effects. And the guidelines don't provide an adequate distinction." Stampfer isn't sure if he'll be invited back to work on the 2005 revision. "I was kind of the odd man out on most of the issues. I think I was on more losing votes than any other member of the committee. I wasn't shy about voicing my opinions. I would welcome it, but I'm not waiting by my phone." —John Fleischman |
