February 12, 2006
Sunday

Aha, so a low-fat diet is bunk and we can all just eat as we please again? Well, not exactly.

Here are some questions and answers about what the latest big diet study did and didn't tell us, and why.

Q: Contradictory diet studies always seem to be making news. One week something's good for you, the next week it's bad. Is this study more significant than most?

A: A lot of the buzz over the data from the Women's Health Initiative studies published Wednesday in The Journal of the American Medical Association came because they were part of a big federal study that seems to contradict conventional diet wisdom of the less fat, the better.

The studies involved nearly 49,000 women, ages 50 to 79 (average age, 62) who were followed for an average of a little more than eight years as 40 percent attempted to follow a low-fat diet (no more than 20 percent of daily calories in fat) and the rest stayed with regular eating habits that included 35 percent to 38 percent fat.

Q: So what did the study measure?

A: Three groups of researchers looked at both groups of women to see how many developed breast cancer, colorectal cancer or heart disease, along with various health measures, such as cholesterol levels. And what they found was that there wasn't much difference in outcome between the two groups, although there was some slight reduction in breast-cancer rates in the diet group, and some heart-health improvements among women who dropped the most fat from their diets.

Q: Then why all the hedging from the experts, if you live just about as healthy on cheeseburgers as salads?

A: Well, for one thing, the women in the study who dieted didn't quite hit the desired low-fat mark. Although they agreed to researchers' request that they try to get no more than a fifth of their calories from fat, and to eat more fruits, veggies and grains, the intervention group didn't meet the goal. During the first year they were in the study, fat made up 24 percent of calories, on average, and by the eighth year had crept up to 29 percent.

"The results do not suggest that people have carte blanche to eat fatty foods without health problems," cautioned Dr. JoAnn Manson, chief of preventive medicine at Harvard's Brigham and Women's Hospital and a co-author of the study.

Q: So was the design of the study flawed?

A: Not really. Diet and health studies tend to be done in several ways. Most studies of large groups just ask people what they eat and drink over some period of time and then measure health outcomes against consumption. The downside of this approach is that researchers don't know for sure that the subjects are eating as they say they are.

At the other end of the spectrum are lab or monitored studies where subjects are allowed to eat only what they're given. But these kinds of arrangements can be made only for small groups of people, and for fairly short periods of time - long enough to measure changes in cholesterol or blood sugar, for instance, but not the onset of major diseases.

In this case, there was an "intervention" for some 19,500 women, but researchers had no effective way of enforcing the change in diet or measuring it beyond what the women told them.

Q: The subjects in this test were all older, postmenopausal women. Doesn't diet earlier in life matter as much or more?

A: That's one of the points that nutrition experts have been making in critiquing the studies - that it would be more meaningful to follow women from middle age for 20 years, or from their teens. "Our diet starts when we are born and it makes sense that what you eat over a lifetime will make a difference,'' said Mara Vitolins, a registered dietitian and associate professor at Wake Forest University who took part in the studies.

Q: The studies seemed to treat all types of fat intake the same. Aren't some fats worse than others?

A: Back in the 1980s, when the study was set up, scientists were just beginning to appreciate that the body digests and uses different types of fat differently. Hardened fats, or trans-fats in margarine, shortening and various fried and baked foods, as well as the saturated fats from meat, are now thought to be most detrimental, while "good" fats from things like olive oil and fish oil actually protect the heart and arteries.

"We've known for some time that 'total fat' is not the issue," said Karen Collins, a nutrition adviser with the American Institute for Cancer Research. "Different kinds of fat affect tumor progression and other aspects of the cancer process in different ways that demand further research."

Q: Did the study take into account other disease-risk factors besides fat intake?

A: The focus was on fat, and did not account for things that other research is increasingly finding to be important contributors to cancer, heart disease and other illnesses - weight and exercise, hormone levels, and, maybe most significant, genetic variations that one day may help us customize our diets to maximize health and minimize disease risk.

Who knows? Some of us may turn out to have genes that let us thrive on fried foods out of a bag. But for now, the best way to live to see that day is still to eat a balanced diet and to exercise.

On the Net:

www.nhlbi.nih.gov

SitNews
Stories In The News
Ketchikan, Alaska