If you were wondering what to make of the definitive eight-year study on dietary fat by the Women's Health Initiative released last week, you're not alone. Even some leading researchers were having trouble figuring out what to say about the study's major conclusion: that a low-fat diet did not significantly reduce disease among nearly 20,000 postmenopausal women, compared with a control group who ate what they wanted.
Was Ross L. Prentice of the Fred Hutchinson Cancer Research Center, one of the authors of the study, sounding slightly defensive when he proclaimed that "women can be confident that cutting back on fat... certainly won't hurt when it comes to maintaining a healthy lifestyle"? (Emphasis added.) Did the food industry waste the billions it spent inventing fat-free cookies?
Well, maybe. The problem, says Dr. Marcia Stefanick of Stanford, who heads the steering committee of the WHI, is that the study was designed back in the early 1990s to test an idea that most researchers were already starting to abandon: that the key to health is the total amount of fat in your diet. Instead, most nutritionists now emphasize controlling calories and eating healthy fats--olive and other unsaturated vegetable oils--while avoiding the bad kinds. So it was no great surprise when The Journal of the American Medical Association reported that researchers had found minor reductions, or none at all, in breast or colon cancer or heart disease among women who cut their fat intake on average to less than 29 percent of total calories. (The control group ate a typical American diet with 35 to 38 percent fat.) Those results "are very consistent with what we've seen" in research over the past decade, says Dr. Walter Willett, the prominent Harvard nutritionist, who calls the craze for low-fat everything a "distraction" from good dietary advice.
And that advice--for both women and men--is just what you've been hearing for the past decade: to avoid trans fats (the partially hydrogenated vegetable oils found in processed foods) and restrict saturated fats from meat and dairy products, while consuming a healthy balance of vegetables, fruits and whole grains. "People should stop thinking low fat is the same as healthy," says Stefanick. "The food industry did a great job of selling that, and people believed them." The other advice from nutritionists hasn't changed, either: to exercise and control total calories to avoid obesity. Exercise is important even apart from its effect on weight: it regulates glucose metabolism (lowering the risk of diabetes) and improves bowel function (which may cut the risk of colon cancer). Obesity appears to cause hormonal changes implicated in breast cancer in postmenopausal women, notes Dr. Michael Thun of the American Cancer Society. In the study, the women who ate a lower-fat diet didn't lose weight, but neither did they gain--a fact that gives small comfort to either side in the great struggle between the authors of low-fat and low-carb diet books.
Even after this definitive study, though, most nutritionists (except for those in the Atkins ultra-low-carb camp) still think there's a benefit to limiting fat consumption. Buried in the larger story of the study was the intriguing statistic that --one subgroup of women did reduce their risk of breast cancer substantially: those who ate the most fat when they entered the study, and made the largest reductions during it.
But the other thing the study showed is how hard it is to adhere to a diet like this. Researchers hoped to test a diet with only 20 percent of calories coming from fat. That's at the butterless-bread, no-oil-salad-dressing level--although very stringent regimens, like the one devised by Dr. Dean Ornish for people at risk of serious heart disease (page 71), go even lower. But the closest participants came, on average, was 24 percent in the first year of the study, a figure that gradually rose to 29 percent by the end. Even those figures, calculated from the women's own reports of what they ate, might include a certain, um, fudge factor. The study participants "got a huge amount of attention and support," Stefanick says. "If we couldn't get them down to 20 percent, we're not likely to achieve that with the general public."
All this advice, of course, comes with the inevitable caveat that it hasn't been tested in a large-scale study like the one released last week. Still, nutritionists agree that the evidence of risk from studies of blood chemistry is much stronger for trans fats and saturated fats than it ever was for the total-fat hypothesis. And some researchers believe that even at eight years, the new study wasn't long enough. Cancer and cardiovascular disease can develop over decades, Prentice says. Which is why Dr. Nieca Goldberg, author of "The Women's Healthy Heart Program," says she plans to tell her patients "exactly what I've been telling them for years." Exercise. Watch your total calories. Avoid harmful fats.