Last week, health news headlines reported that data from the Women's Health Initiative showed that low-fat diets may not offer the health benefits we thought. Dr. Robert Shmerling talked with HEALTHbeat editors about the WHI results and offered some perspective.

What exactly were the results of the Women's Health Initiative study on diet?

In this study, researchers from the Women's Health Initiative — the same research group that uncovered unexpected risks of hormone therapy — looked at the connection between a low-fat diet and a woman's cancer and heart disease risk. More than 48,000 women, ages 50–79, took part. One group of women reduced their fat intake from 38% of daily calories to 29%. A comparison group didn't change their diets at all. After 8 years, both groups had similar rates of breast cancer, colon cancer, and cardiovascular disease.

The study's size and design add weight to its surprising results. It is unlikely that the outcomes were due to chance. And rather than asking about past diet and health problems (a retrospective study, where it can be hard for participants to accurately recount their eating habits), researchers followed these women forward over time and repeatedly monitored their diets and health status.

Does this mean that doctors were wrong about the benefits of a low-fat diet?

Despite the virtues of this study — particularly its size and its design — it is a single study, and leaves some unanswered questions. Therefore, it does not constitute the final word on the subject of nutrition in older women.

What are those questions?

There are several issues still up in the air.

• Was the low-fat diet low enough? Although the study's goal was to have women reduce their fat intake to 20% of calories, the women in the low-fat group cut back to only 29% of calories. It is possible that further scaling back fat intake might have yielded important health benefits.
• What if the dietary changes were made at an earlier age? The average age of the study participants was 62. It is possible that the reduction in fat was not only too little, but too late. This study can't tell us whether cutting back on fat at a younger age (or for a longer time) might reduce disease risk.
• What were the effects of "good" fats and "bad" fats? The WHI did not specifically encourage women to eat "healthy" monounsaturated and polyunsaturated fats (from vegetable oils, nuts, and fish). If women in the study substituted these fats for unhealthy saturated and trans fats (found in meat, processed foods, and some dairy products), the results might have been quite different.
• Were the women followed long enough to identify the benefits? The women on the low-fat diets did experience minor reductions in breast cancer rates and cholesterol levels, as well as slightly fewer cases of pre-cancerous growths in the colon. These findings were so small that they could have been due to chance, but a pattern of more significant improvement might have emerged over a longer time.
• Who benefits most from a low-fat diet? The WHI did not find that any group benefited, but there are limitations as to the conclusions drawn from the study. WHI included only healthy women, so we can't tell what the benefits of a low-fat diet might be for women who already have cancer or heart disease. The WHI also evaluated low-fat diets in postmenopausal women only. It tells us nothing about low-fat diets in younger women or men of any age. Although the result was not statistically significant, there was a trend toward lower rates of breast cancer in women on the low-fat diets. Women with a mother or sister who has developed breast cancer might consider a diet low in saturated and trans fats — along with exercise and weight loss — as ways to reduce their risk for the disease. Also, the results of the WHI suggest that people who already eat a lot of unhealthy saturated and trans fats may especially benefit from consuming less of these fats.
• What is the role of exercise and weight loss? Most of the study volunteers were overweight or obese; none were told to lose weight or exercise. Excess pounds and a sedentary lifestyle may cancel out the benefits of a low-fat diet.

What should women, and men, do now?

A low-fat diet may not be the magic bullet against heart disease or cancer. But there are steps everyone can take to help reduce their risk of these diseases.

• Don't smoke and avoid secondhand smoke. Have your blood pressure, blood sugar, and cholesterol checked. If any of these are consistently elevated, make a plan with your doctor to bring them down.
• Get screened for colon cancer. Talk to your doctor about which screening test (there are several) makes sense for you, and when and how often you should be tested.
• If you are a woman, get regular mammograms and clinical breast exams by your doctor. If you notice any breast changes, let her or him know right away.
• Limit your alcohol intake (up to one drink daily for women, or two daily for men).
• Talk to your doctor about your medical and family history. For example, if colon or breast cancer runs in your family, he or she may recommend earlier or more frequent screening.
• Limit your intake of saturated fat to less than 10% of calories (as recommended by the American Heart Association guidelines) and avoid trans fats. Eat a diet that includes fruits, vegetables, and whole grains.

Whatever your eating habits, regular exercise is an essential part of a healthy lifestyle. For more information on starting an exercise program, order our special health report Exercise: A Program You Can Live With www.health.harvard.edu/E.