Low-Fat Diets and Women's Health New data shows that a low-fat diet did not cut women's risks of breast cancer, colon cancer, stroke or heart attack. A discussion of the study and what it might mean for diet choices.
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Low-Fat Diets and Women's Health

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Low-Fat Diets and Women's Health

Low-Fat Diets and Women's Health

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New data out this week from the Women's Health Initiative has many people scratching their heads. Perhaps you're one of them, because it goes against nutritional advice that we have been hearing for years. Here's what happened.

Researchers tracked the eating habits of nearly 50,000 post-menopausal women for eight years. Now, about 40 percent of the women - that's called the Intervention Group - were asked to follow a diet low in fat, high in fruits, vegetables and grains - all those good, healthy things that we've been told we should be eating. The other women didn't change their eating habits at all. Now, the health of the women in both groups were tracked, and after eight years, the researchers found that the women on the low-fat diet had the same risk of developing breast cancer, colon cancer, heart disease and stroke as the group that ate whatever they wanted.

In other words, according to this study at least, following a low-fat diet does not translate into health benefits. But, before you grab that slice of cheesecake, hold on, because researchers say the study results don't mean you can start piling on the fat again. Joining me now to sort it all out are my guests - both my guests took part in the study, and let me introduce them.

Judith Hsia is a professor of medicine at George Washington University in Washington, D.C. She joins us from her office there. Thanks for being with us today, Dr. Hsia.

Dr. JUDITH HSIA (Professor of Medicine, George Washington University, Washington, D.C.): My pleasure.

FLATOW: You're welcome.

Ross Prentice is a member of the Public Health Sciences Division at the Fred Hutchinson Cancer Research Center. He's also a professor of biostatistics at the University of Washington in Seattle and he joins us today from L.A. Thanks for joining us Dr. Prentice.

Dr. ROSS PRENTICE (Member, Public Health Sciences Division, Fred Hutchinson Cancer Research Center; Professor of Biostatistics, University of Washington, Seattle, Washington): Hi, Ira. Thanks for having us on.

FLATOW: You're welcome.

Dr. Hsia, you know, the headlines, if you listened to the headlines all week, they were saying, hey, you know, you can eat anything you want to -- doesn't matter. True or false?

Dr. HSIA: Well, we definitely don't want that to be the message that people are drawing from the study. I think one thing that--there's several important messages to be drawn. One is that it's very important to do these randomized trials because they're the only way that you can really find out what works and what doesn't.

Another thing to bear in mind with this study is that it was designed to find out if eating a low-fat diet would reduce the risk of breast cancer and that's an area that, actually, Dr. Prentice is the best equipped to discuss. But, because we're always promoting low-fat diets for heart disease prevention, we also investigated whether or not this prevented heart attack and stroke and found that this was not the case.

Now, what actually happened was that the women who were in the intervention group reduced their saturated fat consumption from about 13 percent to about 8 percent which is a good amount, and they had a modest reduction in their LDL, which is the bad cholesterol; it went from 133 to 123. So, it did have a favorable effect, but I guess, to me as a cardiologist, the take-home message is eating a healthful diet is important, but it's not the only thing that you need to do.

FLATOW: Mm hmm. Ross Prentice were you surprised by the results?

Dr. PRENTICE: Of course, we were a little disappointed not to have clear, positive results at this point and time. However, Ira, even though I think a lot of the reporting has been quite good, I believe the headlines have been misleading.

So, whereas the press release from the National Institutes of Health started out Low-fat May Reduce Breast Cancer Risk and May Not Affect Certain Other Diseases, that has mainly been picked up in reports in the media as Low-fat May Not Prevent Cancer and in some cases, Low-fat Doesn't Prevent Cancer or even stronger.

And, I'd also say in relation to your introductory comments that we do not see the study as going against nutritional advice that's been around for years. We studied a particular low-fat diet that didn't try to reduce calories; it attempted to reduce total fat, and also to increase fruits and vegetables, and grains.

So, it was a change of the composition of the diet and as Dr. Hsia mentioned, our primary interest was breast cancer and some of the motivating data, especially from international comparisons where disease rates vary greatly and correlated with the dietary fat habits in particular countries--some of those same trends we saw for colorectal cancer as for breast cancer, so we also studied colorectal cancer. And then in preliminary studies of this particular low-fat eating pattern conducted in the 1980s under the National Cancer Institute auspices, we noted that there was some modest reduction in blood cholesterol, so coronary heart disease was added as a secondary outcome.

But, it's important for your listeners to realize that this was a study primarily focusing on cancer reduction and we actually see our most important results as quite encouraging there, even though not definitive. So, as Dr. Hsia alluded, in breast cancer, we saw a 9 percent lower rate of breast cancer in the low-fat group versus the usual diet group. That is a favorable trend which is not quite statistically significant, but it's actually quite consistent with our expectation going in when one takes account of the amount of dietary difference between the two groups.

FLATOW: But Dr. Prentice, you can't argue with the fact about the results of the diet and pertaining not just to cancer, but to the health of the participants, meaning that there was not a significant difference.

Dr. PRENTICE: So, we have to explain what significant difference means. It's statistically significant so... For example, for breast cancer we have a 9 percent lower rate in the low-fat group versus usual diet group - not quite statistically significant. If it had been 10 percent that would have been statistically significant, so we're close to it being able to assert a benefit for breast cancer and that's why we're - one of the reasons for an additional five years of follow-up which we hope will allow a stronger positive statement in due time.

FLATOW: Dr. Hsia, do you understand the public's confusion with this study?

Dr. HSIA: Oh, absolutely and, in fact, in this week's Circulation there's a survey that was carried out to find out what obstacles are to women's embarking on healthful interventions and, actually, the number one cause was confusion about media reports (laughs) so this may be a classic example. I think that really, the underlying message is for breast cancer prevention, for cardiovascular prevention, that it's not that diet is not important and not helpful, but it's not the only thing you need to do.

So, you need to attain your ideal body weight, exercise regularly, stop smoking, have your cholesterol, your blood pressure and your, you know--if you have diabetes--under good control, and as far as breast cancer prevention is concerned, you know, it's been shown that for high-risk women that interventions like tamoxifen reduce the likelihood of breast cancer and, of course, people should get appropriate cancer screening.

So, I think that the concept that if you eat a healthy diet, you don't need to worry about anything else, is not correct. You know, you need to do more.

FLATOW: Mm hmm. Would it be possible and would it be prudent now to go into other long-term studies like--just off the top of my head--like the Framingham Study and look to see if the results there back up what this study says?

Dr. PRENTICE: So, I could respond Ira, if you wish.


Dr. PRENTICE: One of the challenges in nutritional epidemiology and physical activity epidemiology are the measurement issues, so the usual types of studies we do, like the Framingham Cohort Study, rely very directly on the ability of individuals to accurately report their dietary habits. The fact that that is such a challenge--people report differently at two different points in time, different groups of people may report differently depending on their body mass or ethnicity, or other characteristics--that's actually one of the motivations for this type of expensive, randomized, controlled trial; an actual experiment where women were taught how to make and maintain a dietary change. (Unintelligible).

FLATOW: (Unintelligible)

Dr. PRENTICE: Sorry, go ahead.

FLATOW: Yeah, I know it's hard to go back and see, you know, the control for food. People tell you all kinds of stuff when you ask 'em what they ate (unintelligible).

Dr. PRENTICE: Right, and this type of study design doesn't depend nearly so strongly on the dietary assessment data.

FLATOW: Mm hmm.

Dr. PRENTICE: So we had two groups that by design are equivalent at the beginning in their health risks...

FLATOW: Mm hmmm.

Dr. PRENTICE: ...and we simply compare those two groups in terms of the disease incidence that occurs over the years of follow-up of the study.

FLATOW: If you were to design this study again, today because this is eight years ago or at least...

Dr. PRENTICE: Right.

FLATOW: ...would you do it differently? Would you measure different things? I mean now we know more about trans fats. We didn't talk about them in those days, things like that. Would you try to look between the lines at different kinds of oils that they might have...

Dr. PRENTICE: I'll start, Judith, if it's okay and you can...

Dr. HSIA: Sure.

Dr. PRENTICE: So, if the focus was still primarily on breast cancer prevention, I don't think we have a particularly better idea in terms of a dietary intervention.

FLATOW: Mm hmmm.

Dr. PRENTICE: Of course we think total calories consumed is likely quite important. Some combination of calories consumed and energy expended simply has to be important. That drives obesity and all these are obesity-related diseases.

If one was doing a study with a high priority on coronary heart disease and other cardiovascular diseases, as Dr. Hsia already mentioned, one would want to focus more specifically on saturated and trans-fat reduction, where the epidemiologic data is quite strong.

FLATOW: Dr. Hsia?

Dr. HSIA: Well, I think one thing to bear in mind is that the amount of reduction in the bad cholesterol that women got in our study was about eight percent. And if you take the starting dose of a cholesterol-lowering drug, you can get 40 to 50 percent LDL reduction. So, you know, although diet is useful in, particularly in maintaining ideal body weight, which is a challenge to, you know, all of us and to America as a public health issue, that the amount of impact that you can have on some of these risk factors with lifestyle interventions and diet in particular is limited. And although...

FLATOW: Right, we've been hearing that for years from doctors that say...

Dr. HSIA: Well, but I...

FLATOW: Your liver, your liver likes to make cholesterol you know?

(Soundbite of laughter)

FLATOW: You can cut it back a few percentage points but your liver likes to do it. You'll need something else.

Dr. HSIA: I think docs say that but I think that patients, you know, patients vary obviously; but there's a great tendency to think that well if I was more assiduous in my diet, I could really, you know be off these drugs. And in many cases that's not true.

FLATOW: Mm hmmm.

Dr. HSIA: You know the drugs are a proven benefit of preventing heart attacks, stroke and death which is more than we were able to demonstrate in this study. So that I'm a strong promoter of eating a diet that's low in saturated fat for cardiovascular prevention, but it is vital for people to keep their conventional risk factors under control by whatever means are necessary.

FLATOW: Mm hmmm.

Dr. PRENTICE: I'd like to add, Ira, that...


Dr. PRENTICE: ...important for your listeners to realize that you know this was a particular low-fat diet. There's other low-fat diets. There's many other important questions in dietary prevention of disease that may include calorie reduction and other modifications haven't been subjected to this type of rigorous randomized control trials yet.

FLATOW: Mm hmmm. I want to thank you both for taking time to talk with us today. Ross Prentice is a member of the Public Health Sciences division at the Fred Hutchinson Cancer Research Center and also professor of biostatistics, University of Washington in Seattle. And Judith Hsia is a professor of medicine at George Washington University in Washington. Thank you again for taking time to be with us.

Dr. HSIA: Thank you.

Dr. PRENTICE: Pleasure.

FLATOW: You're welcome.

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