Good Calories, Bad Calories

Belief in the hypothesis persists also because of the time lag involved in research of this nature. In 1991, the National Institutes of Health launched the $700 million Women’s Health Initiative to test the hypothesis (and also the hypothesis that hormone-replacement therapy protects against heart disease and cancer). The WHI investigators enrolled forty-nine thousand women, aged fifty to seventy-nine. They randomly assigned twenty-nine thousand to eat their usual diets, and twenty thousand were prescribed a low-fat diet. The goal was to induce these women to consume only 20 percent of their calories from fat; to do this, they were told to eat more vegetables and fresh fruits, as well as whole grains, in case fiber was beneficial as well. If the diet succeeded in preventing breast cancer, or any chronic disease, the WHI investigators wouldn’t know if it was because these women ate less fat or because they ate more fruits, vegetables, and grains. It’s conceivable that a diet of fruits, vegetables, grains, and more fat, or of vegetables and fruits but less grains, could be even more protective. The women on the diet also consumed fewer calories—averaging 120 calories a day less than the controls over the eight years of the study.^*23 So, similarly, if this diet appeared to prevent cancer, the WHI investigators wouldn’t know whether it did so because it contained less fat (or more fruits and vegetables) or fewer calories. To induce those on the diet to stick to it for the better part of a decade, the WHI investigators provided them with an intensive nutritional and behavioral-education program. The women assigned to eat their usual diets received no such attention, which means they would be considerably less likely to change their lives in other ways that might also have an effect on breast cancer—to exercise or maintain their weight, stay away from sweets, refined flour, fast-food joints, and smoky bars. This disparity in counseling is known as an intervention effect, and it is precisely to avoid such an effect that drug trials must be done with placebos and double-blind.

All of these effects would be expected to bias the trial in favor of observing a beneficial effect where none exists, but the WHI trial still came up negative. In the winter of 2006, the WHI investigators reported that those women who were eating what we today consider the essence of a healthy diet—little fat, lots of fiber, considerable fruits, vegetables, and whole grains, fewer calories—had no less breast cancer than those who ate their typical American fare. (The women on the diet had no less heart disease, colon cancer, or stroke, either.) The results confirmed those of every study that had been done on diet and breast cancer since 1982. This, however, was still not generally perceived as a definitive refutation of the hypothesis. Rose’s logic of preventive medicine held fast (it still does). In a press release on the findings, NHLBI Director Elizabeth Nabel stated, “The results of this study do not change established recommendations on disease prevention.” In editorials that accompanied the WHI articles in JAMA, in virtually every press report, and even in the World Health Organization’s official statement on the trial, it was said that this particular study may have failed to show a beneficial effect of a low-fat, high-fiber diet on breast cancer (and heart disease, stroke, colon cancer, and weight), but that was not a reason to disbelieve the hypotheses. (The WHO press release was entitled “The World Health Organization Notes the Women’s Health Initiative Diet Modification Trial, but Reaffirms That the Fat Content of Your Diet Does Matter.”) Rather than enumerate the ways the WHI trial was biased to find a positive relationship, which was one facet of the controversy in the early 1990s over whether the trial should be funded to begin with, the WHI investigators and those like-minded now enumerated all the reasons why the study might have failed to find an effect.