Of course, even Weight Watchers claims that “diets don’t work; weight watchers does.” Diets may not work, you might be thinking, but what about “healthy eating” or “healthy lifestyle change”? Surely if you eat right you will lose weight, right?
Not so fast. The Women’s Health Initiative Dietary Modification Study was the largest, most extensive, experimental study of “healthy eating” ever conducted. More than 48,000 older women (ages 50-79) were randomly assigned to either eat their usual diet, or eat a low-fat, high fiber, diet with lots of vegetables, fruits, and whole grains — the essence of what most people think of as “healthy eating.”(They chose older women because they wanted to be sure there would be enough incidence of disease among the participants to detect differences between the groups after several years of follow up.)
The women in the intervention group had intensive, state-of-the-art support to maintain their diets — an intensive initial group treatment led by nutritionists, followed by a long-term maintenance intervention group that met regularly over the course of the study, individual counseling, and personalized feedback on their dietary targets and progress. They ate this diet and continued in the intervention program (and were compared to their control-group counterparts) for an average of 8 years of follow up.
They weren’t perfect at maintaining their target diets, of course, but they were pretty good: As Sandy Szwarc notes, “The women in the healthy eating intervention group cut their total fat intakes down to 24% of their calories and 8% saturated fat the first year — well below the control group eating about 38% total fat and nearly 40% more saturated fats. By the end of the study, the “healthy eaters” were still averaging 29% fat, compared to 37% in the control group. The “healthy” dieters also ate about 25% more fruits and vegetables, grains and fiber than the typical American diet of the control group.”
So, what do you suppose were the benefits of the healthy diet these women maintained faithfully for 8 years?
- There was no advantage in terms of cardiovascular disease, including heart disease and stroke, for the healthy eating women.
- There was no advantage in terms of breast cancer, colorectal cancer, or any of 30 other cancers, except possibly ovarian cancer, and the researchers note that this one, modest, effect, may be due only to chance.
- And despite maintaining a restricted diet for 8 years — at follow up, they were eating an average of 361.4 kcal/day less than they had been eating at baseline — these women lost a total of about one pound, on average, compared to the women who ate as they pleased.
These women successfully changed their eating lifestyles for 8 years: more fruits and vegetables, more whole grains, less fat, less calories. Classes, nutrition groups, hearing feedback about how they were doing. (“Couldn’t you cut out the chocolate, Ann-Marie?”) Yet they didn’t do better in terms of cardiovascular health, or cancer. They lost only a pound, for 8 years of effort. Would that be worth it to you?