So what do women do now? The results of two major studies over the past two weeks have questioned the value of two widely recommended measures: calcium pills and vitamin D to prevent broken bones, and low-fat diets to ward off heart disease and breast and colon cancer.
Should women abandon hope, since it looks as if nothing works? Abandon guilt and assume diet makes no difference? Or muddle on with salad and supplements, just in case?
The studies — part of the same government research project that in 2002 found hormone treatment for menopause did more harm than good — have confused women and prompted renewed examination of the regimens that many have been carefully following. Researchers find themselves parsing the results, and debating about how far the scientific rules can be stretched when it comes to measuring results and searching for evidence in smaller groups of patients within a large study.
The researchers admit that the findings were an unexpected and puzzling challenge to firmly held, almost religious beliefs about nutrition and health. And though some experts said the results meant women should look for other ways to prevent heart disease, cancer and bone loss, the scientists who conducted the studies insisted that hints of benefit in parts of the data could not be ignored.
"We just didn't come out with as strong a finding as everyone expected," said Dr. Marcia L. Stefanick, head of the study's steering committee. "The results weren't clear enough, weren't black and white."
"We're still debating amongst ourselves," Dr. Stefanick said.
The studies, which involved thousands of women and cost hundreds of millions of dollars, were the largest and most rigorous look ever at the effects of diets and supplements, and are unlikely to be repeated.
News of the findings spread rapidly, and women interviewed in several cities were aware of them.
Pouran Zamani-Hariri, 68, of Chicago, said she had been taking calcium and vitamin D every day for five years and planned to ask her doctor about the calcium study. But the results did not surprise her, Ms. Zamani-Hariri said, because despite taking the supplements, she has broken her shoulder and her leg within the last two years. "Maybe it proves that it doesn't work," she said.
Kim Curtis, 39, a portfolio accountant from Winthrop, Mass., said she chose full-fat foods over reduced-fat products because she worried about sugars and preservatives being used to replace fat in processed food. "The way things are, you're going to get cancer anyway," Ms. Curtis said.
But the researchers who conducted the study said their findings were not a signal to binge on bacon cheeseburgers.
"I was a little uncomfortable with some of the reactions," said Dr. Jacques Rossouw, the project officer for the Women's Health Initiative, the program that has created the stir. It worries him, he said, that some people think the studies mean fat and calcium do not matter.
"It's not what we say, and I don't think it's what the papers say," Dr. Rossouw said.
"For folks who are on a low-fat diet, by all means continue," he added. "If you're on a high-fat diet, certainly get it down. That's the message we would like to send."
As for calcium and vitamin D, he said, the recent study had "enough hints" of benefit that women whose diets do not provide adequate amounts should take supplements.
The studies were part of the health initiative, which started in the 1990's. The one on the low-fat diet, which included nearly 49,000 women ages 50 to 79, found that overall, after eight years, the diet had no effect on the rates of breast cancer, strokes, heart attacks or colon cancer.
Similarly, the calcium study, which included more than 36,000 women, found that taking supplements for seven years did not prevent broken bones or colorectal cancer, but it did produce a 1 percent increase in bone density in the hip.
Given the findings, then, how can researchers like Dr. Rossouw still recommend low-fat diets and supplements? The answer depends on how one interprets data. These studies included women who were treated and a control group that took placebos or, in the diet study, ate whatever they wanted. The researchers tracked their health, comparing the groups.
According to standard rules based on probability, the difference in results between the groups has to be of a certain size to qualify as a genuine, or statistically significant, difference, and not something that could happen by chance.
In the diet study, the difference in breast cancer rates was not statistically different. But Dr. Rossouw said it was so close — a 9 percent reduction in risk, whereas 10 percent would have been significant — that if the study had gone on longer, it might well have become significant. That was one of his main reasons for continuing to defend a low-fat diet. In addition, he said, the women who started out eating the most fat and then reduced their intake seemed to have the biggest reduction in risk.
