TOPICS > Health

New Study Shows Low Fat Diet May Not Go Far Enough

February 8, 2006 at 12:00 AM EDT


MARGARET WARNER: For years some nutritionists and food makers promoted the idea that a low-fat diet could help prevent cancer and heart disease. But a major study by the Women’s Health Initiative, published today in the Journal of the American Medical Association, found that simply reducing the amount of fat in a diet doesn’t provide those health benefits.

The 12-year project involving nearly 49,000 post-menopausal women found that low-fat diets did not significantly reduce the risk of breast cancer, colon cancer or heart attacks and strokes. The federally-funded study made no distinction among the types of fat the women consumed.

For more on these results and their implications, I’m joined by Barbara Howard, a lead investigator in the studies — she is president of the Med Star Research Institute; and Dr. Peter Libby, chief of cardiovascular medicine at Brigham and Women’s Hospital in Boston. He was not involved with the study. Welcome to you both.

Barbara Howard, the headline today in all the papers was “low fat diet, no effect on heart disease or cancer.” Is it that simple or was there more nuance to it than that?

BARBARA HOWARD: I think it’s not that simple. And I think being that this is the longest and largest diet study we’ve ever had and we’ve learned a lot from it, starting with breast cancer, although the difference was not significant, there was a 9 percent reduction in breast cancer, which was almost statistically significant. And in addition to that –

MARGARET WARNER: That is, the women who had the lower-fat diet did have 9 percent less.

BARBARA HOWARD: That’s right.

MARGARET WARNER: Risk of breast cancer.

BARBARA HOWARD: That’s right. Thank you.

MARGARET WARNER: I just want to make sure we understand that.

BARBARA HOWARD: Absolutely yes and. But we found that the women who started out with a higher amount of fat in their diet and made a bigger drop had a greater reduction. And it was statistically significant.

In addition, we learned a whole lot about types of fat, which reinforced what we have thought about the role of specific fats in heart disease. If you look at the data on heart disease, again, there was not much reduction in saturated fat. The women only dropped their saturated fat about 3 percent. That led to about a three-point drop in LDL, your bad cholesterol and therefore a very small change in heart disease.

MARGARET WARNER: By saturated fat just to be clear to people who don’t monitor this all the time we’re talking about basically dairy fats and fats from meat versus the so-called good fats like olive oil.

BARBARA HOWARD: That’s right. And to go on further on that line of thought, when we looked at the women who did achieve a lower level of saturated fat, the one you get from meats and dairy products, animal products, or transfat, and you’ve heard a lot about that –

MARGARET WARNER: That’s the fats in processed foods.

BARBARA HOWARD: That’s right. Those women did get a greater drop in their LDL level and a bigger improvement in their heart disease which was significant.

MARGARET WARNER: Dr. Libby, were you surprised at these results –Because the headline looked at overall fat intake; was there a significant, well established body of opinion in the medical community that overall fat in and of itself was important? Was this a surprising finding?

DR. PETER LIBBY: Well, that was certainly the burning question when this study was designed a dozen years ago. But since this study was designed — and it’s really a very important study and superbly executed — the ideas have evolved.

Now we’d like to pose the question with an equally and powerful and well designed and executed study not, is it important to have low fat but what kind of fat is important?

This study very nicely swapped fat for carbs because the carbohydrate intake rose to balance the decrease in calories from fat. And what I think we need next in order to elucidate the role of fats in cardiovascular protection is a study that would say, well, let’s swap out what you characterize as the bad fats, those that are saturated, and replace them with the fats that we now consider are beneficial or potentially beneficial for cardiovascular disease such as the monounsaturated and polyunsaturated fats.

Those are the kinds of fats you get in the oils that when you walk down the supermarket aisle are liquid at room temperature and the ones that we think, grossly speaking, are less healthy for the heart and blood vessels are those that are solid at room temperature, such as the shortenings and margarine and butter.

MARGARET WARNER: You were going to add –

BARBARA HOWARD: Yes. Dr. Libby is very correct about the fact that studies always open up questions that lead to the next study.

Also, he mentioned that we did lower the fat and replace it with carbohydrate. And I think we learned some very valuable things about that especially now because of the current carbo-phobia that’s been prevalent.

MARGARET WARNER: Let me stop you there just for a minute. Tell us more about this with these women. I gather they were post-menopausal. Many of them were overweight. Is that right?

BARBARA HOWARD: That’s right.

MARGARET WARNER: And the ones that cut back on their fat, whatever kind of fat they cut back, did they then replace it with healthy food or did they load up on sugary, refined sugar carbohydrates?

BARBARA HOWARD: Well, they were counseled to replace their fat with carbohydrates in the forms of vegetables, fruits and grains. They did increase their vegetable and fruit serving one-and-a-half a day. They got up to five a day and they did increase their grains about half of a day.

And we have not analyzed yet — the data are still being analyzed that will tell us exactly what kind of carbohydrate they were eating. But nevertheless, this established the relative safety of a diet that did replace some fat with carbohydrate.

MARGARET WARNER: Dr. Libby, you said this was a very good and well designed study but do you consider it a major drawback that it didn’t go ahead, I mean, they were looking at 49,000 women — they didn’t go ahead and make three different groups, one that really cut back on the saturated fats and one that followed the Mediterranean diet — we know the three groups — we just described them — rather than this rather cruder measurement of just all fat lumped in one category?

DR. PETER LIBBY: Well, you know, hindsight is 20/20. In order to have a powerful experiment, you have to focus on a few groups with sufficient numbers to answer the question in a statistically valid way so I view this as one hypothesis tested and that is swapping out fat for carbohydrate. That didn’t seem to confer great benefits either for the cancer end points or for the heart and blood vessel end points.

And I look forward to a similar intervention study where instead of making observations on groups of people based on recall, looking backwards, we can look forward and actually do an experiment like was done so well in this study, where we have a scientifically controlled experiment with one dietary variable pitted against another and ask the next question, which would have to do, in my view, with the good fats versus the bad fats.

I think it’s very important that the listeners not take this as a license to chow down on cheeseburgers because the overall caloric content is probably as important if not more important than the specific food components, so unless your calorie intake equals your calorie expenditure, you’re setting yourself up for gaining weight. And we know that that has horrendous consequences for cardiovascular health.

So that message I think is very important for our viewers that this does not mean that you can go and have a high fat diet and forget about calories and forget about physical activity.

MARGARET WARNER: And, Barbara Howard, if we’re talking to viewers who have been following the so-called Mediterranean diet, that is they’ve reduced their saturated fat, would you say to them continue with that or the jury is out?

BARBARA HOWARD: Yes, I think that our study does support the national guidelines, which allow a rather wide range in intake of total fat but want people to focus on the type of fat.

And in the Mediterranean diet, there is a low level of saturated and transfat, and there is a higher level of mono and polyunsaturated.

MARGARET WARNER: And just briefly why didn’t you break it down into the three different groups?

BARBARA HOWARD: For exactly the reason that Dr. Libby told you. It would have taken about 100,000 women to be able to have the three groups because of the fact that we are looking at actually chronic diseases, which are not that frequent even in this age women.

I do want to also emphasize another point that he made, and that had to do with overall weight and health. The biggest problem for nutrition in this country is overweight. And I think that this diet showed that there were no adverse effects on weight. We actually saw a small weight loss in the women in the intervention group.

MARGARET WARNER: In the lower-fat group.

BARBARA HOWARD: In the lower-fat group. In addition, the overall safety profile despite all the claims about raising your carbohydrate was very good. Insulin levels didn’t go up. Triglyceride levels didn’t go up, et cetera, et cetera.

So the main thing is if people would eat less and be more active, this kind of a dietary pattern you could say to them will be safe for them in the long haul.

MARGARET WARNER: So no magic bullet, in other words. You’re both saying watch your calories. It still matters what you eat and exercise.


MARGARET WARNER: Dr. Libby, this is a women’s health study that has looked at other things like hormone replacement therapy, but do you think from the point of view of being a cardiologist that these results are applicable to men as well?

DR. PETER LIBBY: Well, first of all, let’s not overlook that this is a study, a large study that was designed to focus not just on breast cancer and colon cancer but also on cardiovascular end points.

And I think particularly in the month of February which we have declared the Go Red for Heart Month by the American Heart Association to point out the importance of cardiovascular disease in women that heart disease is probably six to ten times more likely to kill a woman than breast cancer. That doesn’t mean that the breast cancer is not terribly important but we do have to applaud this study because it focused on women.

Traditionally cardiovascular studies have neglected women. We need to redress that. And this study is a very important step in that direction. The other reason I have to congratulate these investigators is because they tackled a tough problem. You know, the drug companies are all lined up to try to sponsor studies that will show that a medicine may be better than one other medicine or no treatment.

But the pharmaceutical industry and the private sector is not going to sponsor these critically important studies to look at lifestyle variables. You can see that the perceived notions or assumptions sometimes are not borne out by experiment.

That’s why it’s really critically important for us to continue investing in research in studies like this one made by the National Heart, Lung and Blood Institute to answer these critical questions which will never be answered without federally funded research support.

MARGARET WARNER: All right. And thank you both. We’re going to have to leave it there. Thank you.