Last week, researchers conducting a long-awaited study on the effectiveness of low-fat diets dropped a bombshell: Eating a low-fat diet does not appear to reduce the risk of getting breast cancer, colorectal cancer, or cardiovascular disease.

The $415 million study, part of the Women's Health Initiative, followed nearly 49,000 women aged 50 to 70 over eight years. It was the largest, longest, and best-designed study ever to test the merits of a low-fat diet.

To help sort out what to make of the new research, Globe columnist Judy

Foreman and staff writer Carey Goldberg posed questions about the study to five leading experts on diet, heart disease, cancer, metabolism, and preventive medicine.

They all agreed on one thing: Although the study failed to prove a strong link between low-fat diet and better health, "it's not really license to head for the butter," as Dr. Michael Thun, chief epidemiologist for the American Cancer Society, put it.

They all pointed to other research though often less definitive than the new study suggesting that the most heart-protective diet includes lots of fruits, vegetables, whole grains, fish, and "good" fats like omega 3 fatty acids and olive oil.

The new study "is probably the final nail in the coffin for low-fat

diets," said Dr. Walter Willett, chairman of the department of nutrition at Harvard School of Public Health. "But people should not conclude that diet is not important. The right dietary choices can make a huge difference in long-term well-being. . . . It's just this particular diet that doesn't matter."

Other excerpts from their responses:

Q: After considering the new data, what diet would you tell your patients to follow?

§        Dr. Michael Dansinger, an obesity and nutrition expert at Tufts-New England Medical Center: "Based on current evidence, I would recommend a high fruit and vegetable diet, low in saturated fat, low in refined starch and sugar, and moderate in low-fat protein and fish/seafood."

§        Dr. Christopher Cannon, cardiologist, Brigham and Women's Hospital: With any diet, "you've got to do it for decades, not just a little quick fix and you're done. . . . You do have to stick with it."

Q: The women in the study were able to reduce their consumption of fat from about 38 percent of the calories they ate to 25 to 29 percent instead of the hoped-for 20 percent. Does this mean a truly low-fat diet is impossible for most people?

§        Dr. JoAnn Manson, study author and chief of preventive medicine at Brigham and Women's, said yes, explaining that the study: "suggests that it will be very difficult to implement this low-fat diet on a population-wide basis without societal, environmental, and food industry changes. This dietary intervention did not achieve its goal even though the women in the diet change group got intensive counseling and were highly motivated and dedicated."

Q: Do the findings support a more sophisticated definition of "fat"? Has our understanding that not all fats are created equal which has gained currency since the study was started made the findings obsolete in terms of heart disease?

§        Dansinger: "There is practically unanimous agreement that the kind of fat matters. Different fats have different effects. There is general agreement that the fats from worst to best are: trans fats, saturated, polyunsaturated, mono unsaturated, vegetarian omega 3, fish-derived omega 3. Fat-containing foods often have a combination of these fat types."

§        Willett: "This shouldn't be taken as permission to load up on cheeseburgers and french fries, because we do have information that the type of fat is important for reducing risk of heart disease and type 2 diabetes. Replacing unhealthy fats, trans fats, and saturated fats with nonhydrogenated vegetable oils can have major benefit for reducing heart disease risks."

§        Thun: "This study examined the narrow question of whether reducing total fat in postmenopausal women would prevent breast cancer, colon cancer, and heart disease. That question was a hot topic in 1993 when the Women's Health Initiative began. But really the whole field of nutrition and chronic disease has moved on considerably since that question."

Q: Why, then, did you test the idea of lowering total fat instead of just restricting the bad fats?

Manson: The primary goal of the study was to test the theory that reducing total fat to 20 percent of calories would lower the risk of breast and colorectal cancer. If the main goal of the study had been to reduce cardiovascular disease, we would have asked women to reduce saturated and trans fats only. We expected that cutting fat calories across the board would lead to enough change in saturated and trans fats to lower risks of cardiovascular disease, but the changes in "bad fats" weren't large enough to do so.

Q: Has diet been overrated as a means to promote health?

§        Dansinger: "Unhealthy diet and sedentary lifestyle clearly shorten lifespan and promote cancer and heart disease, but there is much legitimate debate and lack of evidence regarding how best to advise people and, more importantly, how to help people fully implement the advice."

Q: Does the study suggest that genes are more powerful than diet in

affecting health?

§        Willett: "No. We know from lots of other studies that when people migrate" to the United States from countries such as Japan and China, "colon cancer rates go up tenfold, breast cancer rates go up fivefold, heart disease rates more than triple. So we know the high rates in this country are not due to genetic factors that diet and lifestyle are very important."

§        Dansinger: "It is not that genes are too powerful an influence for diet to have much of an effect, it is that our attempts to change diet have been too weak to overcome a toxic food environment. This study proves that moderately cutting fat is insufficient."

Q. Are exercise and weight control more important than diet for preventing cancer and heart disease?

§        Dansinger: "I would agree that exercise, not smoking, and controlling your weight are more important than the type of diet. However, the type of diet is still likely to be very important in terms of long-term risk of disease. We lack proof, but there is ample evidence to support this belief."

§        Manson: "We wanted to modify the composition of the diet without restricting caloric intake. The diet trial was not intended to address exercise or weight loss. If substantial weight loss had occurred, which it did not, that in itself might explain changes in risk factor status, which would confound the trial's results."

Q: Did the study find any link between a low-fat diet and breast cancer?

§        Manson said yes, explaining: "There was a suggestion that at least the women who started out with a high-fat diet more than 37 percent fat may benefit from lowering" the total amount of fat they consume. "It's clear this dietary pattern doesn't reduce heart disease and stroke that's the reason it should not be implemented on a population-wide basis. The women who are at increased risk of breast cancer and start out at a very high dietary intake of fat, they may want to cut their total fat intake."

Q: Is it just that it's too hard to study the link between diet and health because diseases like cancer are affected by the accumulation of a lifetime of eating habits and other factors?

§        Dansinger: "The kinds of studies that provide definite answers are expensive and time-consuming and are very difficult to design. Is eight years long enough? Probably not." But, "it is definitely enough time" to see whether a diet will help prevent heart disease.

§        Manson: "It may take greater changes in fat intake and fruits and vegetables and whole grain intake [than made by the people in the study] in order to see benefits for cancer and cardiovascular disease."

§   Willett: "The perfect study is probably never going to be possible. One of the sobering lessons is that large randomized trials" like the Women's Health Initiative "may not be a good way to study the effects of diet on cancer risks."

Judy Foreman’s column appears every other week. Past columns are available on www.myhealthsense.com .

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