New data on health: Studies in confusion

One of the biggest problems in this kind of research is deciding exactly what to test. When the initiative was being planned, for example, studies that looked at what people in different countries ate indicated that the total amount of fat consumed appeared to have a major effect on the risk of certain cancers, especially breast and colon cancers. So the project set out to test that idea by studying more than 48,000 women, working intensively to get half of them to eat less fat and more fruits and vegetables. Because the study was also examining the effects of taking hormones on heart disease, researchers decided to examine whether that diet could reduce that risk as well.

The final results found no overall reduction in the risk for any of those illnesses, which did not surprise Stampfer and others who lobbied against doing the low-fat study. "My view at the time was that this was not a hypothesis that was strong enough to warrant testing at such great expense," Stampfer said. "Other people looked at the same data and interpreted it differently."

Rossouw and others said the decision was justified based on what was known at the time. "There was data coming from a number of international studies and from people born outside the United States who moved here and increased their fat intake," said Elizabeth G. Nabel, director of the Heart, Lung and Blood Institute. "Based on that, it was very reasonable at that time to believe that lowering your total fat would reduce your risk for breast cancer and colon cancer."

Disputed findings
And that may still turn out to be correct, several researchers said. The study came close to showing a statistically meaningful reduction in breast cancer among women on the low-fat diets, and it did find a reduced risk for some subgroups of women, such as those who were eating the most fat at the outset and cut their fat intake the most over the next seven years.

Other scientists dispute those findings, saying those kinds of interpretations are often misleading and unreliable. "Even if you do see a small benefit for, say, breast cancer, you couldn't be sure it was due to fat and not due to the fact that the women also increased their fruit and vegetable intake and there was also a small weight loss," said Walter Willett of the Harvard School of Public Health. "I think it's clear this study was a mistake."

Rossouw and others said the problem could have been that too few women in the study cut their total fat sufficiently for long enough for a clear benefit to emerge. By the time the study began signing up volunteers, a lot of women were eating less fat than when the project was conceived. And as the study progressed, those on the low-fat diet managed to cut their fat less than had been hoped, which made the difference between the two groups much smaller than anticipated.

Complying with requirements
That illustrates another problem: It is often much harder to get people to make significant changes -- and to be honest about it -- than researchers expect. Even though the women in the study were highly motivated, their compliance with the study's requirements fell far short.

The same was true for the calcium and Vitamin D study. Many women took supplements less regularly than expected. And more women in the comparison group started taking supplements on their own, which made the difference between the two groups less than might have been needed to show a clear benefit. Many women also started to take prescription drugs to prevent bone-thinning, further muddying the results.

Although the study found the supplements increased bone density slightly and decreased the risk of hip fractures for older women and those taking their supplements regularly, there was no overall reduction in broken bones. The supplements also increased the risk for kidney stones.

Picking the right group to study can be tricky. In the hormone study, researchers focused primarily on elderly women because they face the greatest risk of heart attacks. The study found that estrogen not only did not protect their hearts, it increased the risk of heart attacks, strokes and breast cancer.

But because so few younger women were included in the study, an intense debate continues about whether the hormone may protect their hearts if they take it before their arteries start to become diseased.

The failure to show a benefit from low-fat diets in preventing heart disease stems from the decision to add that question, almost as an afterthought, to a study that originally focused on cancer. Researchers knew that the key to preventing heart disease was lowering saturated fat. But because the focus of the study was total fat, most of the women did not reduce their saturated fat enough to make a major difference.

"I think we should have lowered expectations of what a lifestyle intervention trial can show over a relatively short period of time," Rossouw said. "Against a climate of less research funding overall, it's going to be harder to do these kinds of trials in the future."

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