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| Volume 50, Number 3, Summer 2001 |
THE SOFT SCIENCE OF DIETARY FAT[The following is an excerpt] by Gary Taubes
When the U.S. Surgeon General's Office set off in 1988 to write the definitive report on the dangers of dietary fat, the task appeared straightforward. Four years earlier, the National Institutes of Health (NIH) had begun advising every American old enough to walk to restrict fat intake, and the president of the American Heart Association (AHA) had told Time magazine that if everyone went along, "we will have [atherosclerosis] conquered" by the year 2000. The Surgeon General's Office itself had just published its 700-page landmark "Report on Nutrition and Health," declaring fat the single most unwholesome component of the American diet. All of this was apparently based on sound science. So the task before the project officer was merely to gather that science together in one volume, have it reviewed by a committee of experts, and publish it. The project did not go smoothly, however. Four project officers came and went over the next decade. Finally, in June 1999, 11 years after the project began, the Surgeon General's Office circulated a letter, authored by the last of the project officers, explaining that the report would be killed. There was no other public announcement and no press release. Bill Harlan, a member of the oversight committee and associate director of the Office of Disease Prevention at NIH, says, "the report was initiated with a preconceived opinion of the conclusions," but the science behind those opinions was not holding up. During the past 30 years, the concept of eating healthy in America has become synonymous with avoiding dietary fat. An entire research industry has arisen to create palatable nonfat fat substitutes, and the food industry now spends billions of dollars yearly selling the less-fat-is-good-health message. The government weighs in as well, with the U.S. Department of Agriculture's (USDA's) booklet on dietary guidelines and its ubiquitous Food Guide Pyramid, which recommends that fats and oils be eaten "sparingly." The low-fat gospel spreads farther by a kind of societal osmosis, continuously reinforced by physicians, nutritionists, journalists, health organizations, and consumer advocacy groups such as the Center for Science in the Public Interest, which refers to fat as this "greasy killer." As the Surgeon General's Office discovered, however, the science of dietary fat is not nearly as simple as it once appeared. The proposition that dietary fat is a bane to health is based chiefly on the fact that fat, specifically the hard, saturated fat found primarily in meat and dairy products, elevates blood cholesterol levels. By the 1970s, each individual step of the chain from fat to cholesterol to heart disease had been demonstrated beyond reasonable doubt, but the veracity of the chain as a whole has never been proven. In other words, despite decades of research, it is still a debatable proposition whether the consumption of saturated fats above recommended levels by anyone who's not already at high risk of heart disease will increase the likelihood of untimely death. Nor have hundreds of millions of dollars in trials managed to generate compelling evidence that healthy individuals can extend their lives by more than a few weeks, if that, by eating less fat. Since the early 1970s, Americans' average fat intake has dropped from over 40 percent of total calories to 34 percent; average serum cholesterol levels have dropped as well. But no compelling evidence suggests that these decreases have improved health. Although heart disease death rates have dropped-and public health officials insist low-fat diets are partly responsible-the incidence of heart disease does not seem to be declining, as would be expected if lower fat diets made a difference. This was the conclusion, for instance, of a 10-year study of heart disease mortality published in the New England Journal of Medicine in 1998, which suggested that death rates are declining largely because doctors are treating the disease more successfully. Meanwhile, obesity in America, which remained constant from the early 1960s through 1980, has surged upward since then-from 14 percent of the population to over 22 percent. Diabetes has increased apace. Both obesity and diabetes increase heart disease risk, which could explain why heart disease incidence is not decreasing. That this obesity epidemic occurred just as the government began bombarding Americans with the low-fat message suggests the possibility, however distant, that low-fat diets might have unintended consequences-among them, weight gain. The history of the national conviction that dietary fat is deadly, and its evolution from hypothesis to dogma, is one in which politicians, bureaucrats, the media, and the public have played as large a role as the scientists and the science. It's a story of what can happen when the demands of public health policy-and the demands of the public for simple advice-run up against the confusing ambiguity of real science. Like the flourishing American affinity for alternative medicine, an anti-fat
movement evolved independently of science in the 1960s. It was fed by
distrust of the establishment-in this case, both the medical establishment
and the food industry-and by counterculture attacks on excessive consumption,
whether manifested in gas-guzzling cars or the classic American cuisine
of bacon and eggs and marbled steaks. And while the data on fat and health
remained ambiguous and the scientific community polarized, the deadlock
was broken not by any new science, but by politicians. It was Senator
George McGovern's bipartisan, nonlegislative Select Committee on Nutrition
and Human Needs that almost single-handedly changed nutritional policy
in this country and initiated the process of turning the dietary fat hypothesis
into dogma. McGovern's committee listened to two days of testimony on diet and disease in July 1976. Then resident wordsmith Nick Mottern, a former labor reporter for The Providence Journal, was assigned the task of researching and writing the first "Dietary Goals for the United States." Mottern, who had no scientific background and no experience writing about science, nutrition, or health, believed his Dietary Goals would launch a "revolution in diet and agriculture in this country." He avoided the scientific and medical controversy by relying almost exclusively on Harvard School of Public Health nutritionist Mark Hegsted for input on dietary fat. Hegsted had studied fat and cholesterol metabolism in the early 1960s, and he believed unconditionally in the benefits of restricting fat intake, although he says he was aware that his was an extreme opinion. Mottern's report suggested that Americans cut their total fat intake to 30 percent of the calories they consume and saturated fat intake to 10 percent, in accord with AHA recommendations for men at high risk of heart disease. The report acknowledged the existence of controversy but insisted Americans had nothing to lose by following its advice. "There are [no risks] that can be identified and important benefits can be expected," Hegsted wrote. This was an optimistic but still debatable position, and when Dietary Goals was released in January 1977, "all hell broke loose," recalls Hegsted. "Practically nobody was in favor of the McGovern recommendations. Damn few people." McGovern responded with three follow-up hearings. Among those testifying was NHLBI director Robert Levy, who explained that no one knew if eating less fat or lowering blood cholesterol levels would prevent heart attacks, which was why NHLBI was spending $300 million to study the question. Levy's position was awkward, he recalls, because "the good senators came out with the guidelines and then called us in to get advice." He was joined by prominent scientists who testified that advising Americans to eat less fat on the strength of such marginal evidence was equivalent to conducting a nutritional experiment with the American public as subjects. Even the American Medical Association protested, suggesting that the diet proposed by the guidelines raised the "potential for harmful effects." But as these scientists testified, so did representatives from the dairy, egg, and cattle industries, who also vigorously opposed the guidelines for obvious reasons. This juxtaposition served to taint the scientific criticisms. The guidelines might have then died a quiet death when McGovern's committee came to an end in late 1977 if two federal agencies had not felt it imperative to respond. Although they took contradictory points of view, one message-with media assistance-won out. The first was the USDA, where consumer-activist Carol Tucker Foreman had recently been appointed an assistant secretary. Foreman believed it was incumbent on USDA to turn McGovern's recommendations into official policy, and, like Mottern, she was not deterred by the existence of scientific controversy. "Tell us what you know and tell us it's not the final answer," she would tell scientists. "I have to eat and feed my children three times a day, and I want you to tell me what your best sense of the data is right now." Of course, given the controversy, the "best sense of the data" would depend on which scientists were asked. The Food and Nutrition Board of the National Academy of Sciences (NAS), which decides the Recommended Dietary Allowances, would have been a natural choice, but NAS president Philip Handler, an expert on metabolism, had told Foreman that Mottern's Dietary Goals were "nonsense." Foreman then turned to McGovern's staffers for advice and they recommended she hire Hegsted, which she did. Hegsted, in turn, relied on a state-of-the-science report published by an expert but very divergent committee of the American Society for Clinical Nutrition. "They were nowhere near unanimous on anything," says Hegsted, "but the majority supported something like the McGovern committee report." The resulting document became the first edition of "Using the Dietary Guidelines for Americans." Although it acknowledged the existence of controversy and suggested that a single dietary recommendation might not suit an entire diverse population, the advice to avoid fat and saturated fat was, indeed, virtually identical to McGovern's Dietary Goals. Three months later, the NAS Food and Nutrition Board released its own guidelines: "Toward Healthful Diets." The board, consisting of a dozen nutrition experts, concluded that the only reliable advice for healthy Americans was to watch their weight; everything else, dietary fat included, would take care of itself. The advice was not taken kindly, however, at least not by the media. The first reports criticized the NAS advice for conflicting with the USDA's and McGovern's and thus somehow being irresponsible. Follow-up reports suggested that the board members, in the words of Jane Brody, who covered the story for the New York Times, were "all in the pocket of the industries being hurt." To be precise, the board chair and one of its members consulted for food industries, and funding for the board itself came from industry donations. These industry connections were leaked to the press from the USDA. Hegsted now defends the NAS board, although he didn't at the time, and calls this kind of conflict of interest "a hell of an issue." "Everybody used to complain that industry didn't do anything on nutrition," he told Science, "yet anybody who got involved was blackballed because their positions were presumably influenced by the industry." (In 1981, Hegsted returned to Harvard, where his research was funded by Frito-Lay.) The press had mixed feelings, claiming that the connections "soiled" the academy's reputation "for tendering careful scientific advice" (Washington Post), demonstrated that the board's "objectivity and aptitude are in doubt" (New York Times), or represented in the board's guidelines a "blow against the food faddists who hold the public in thrall" (Science). In any case, the NAS board had been publicly discredited. Hegsted's Dietary Guidelines for Americans became the official U.S. policy on dietary fat: Eat less fat. Live longer. # Gary Taubes is a staff writer for Science. "The Soft Science of Dietary Fat," Science, 30 March 2001. Published with permission. |
