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StumbleUponStudying the Low-Fat Diet
In Woody Allen's movie ''Sleeper,'' a man wakes up 200 years in the future to find that science has proved deep-fried foods to be healthy. Is the future here already?This week, the Journal of the American Medical Association published a series of articles from the Women's Health Initiative. The 49,000 women who participated in this study are heroes. They gave their most precious commodity -- their time -- to help answer one of the most important health questions of our time: will a "low-fat diet" reduce the risk of coronary heart disease, stroke, breast cancer, and colon cancer?
It didn't.
Around the world, headlines blared, "Low-Fat Diet Does Not Cut Health Risks." Around the office cooler, many people were saying, "I'm thoroughly exasperated by all this contradictory information. If the doctors can't make up their minds, to hell with 'em, I'll just eat and do whatever I want and quit worrying about it!"
That would be most unfortunate. Science can help people distinguish what's true from what isn't, what sounds good from what's real. Nowhere are the claims more conflicting than in the area of diet and nutrition. This is an area where misinformation can make a huge difference to your health and well-being.
Unfortunately, the study was not designed very well. Even if a study of a diet has 49,000 women and spends $450 million, it's not going to show very much if people don't follow the diet. And it's not going to show very much if both groups changed their diet about the same. That's what happened.
The problem with this study is that the women didn't change their diet very much. They were asked to reduce their dietary fat down to 20% of calories, but they only reported reducing it to 29%. It's unlikely they even did that well, since they reported reducing their caloric intake from 1,700 to 1,500 calories a day, but they didn't lose weight. (It's very common for people to report that they're following a diet better than they really are.) Their LDL ("bad") cholesterol levels decreased only 2.6% more in the low-fat diet group than in the comparison group, hardly any difference at all. Blood pressure decreased hardly at all in either group, only about 2% in both groups.
Given how small the changes in diet were, it's not surprising that there were little effects. If you don't change much, you don't improve much.
By analogy, it's as though the women in one group reduced the number of cigarettes they smoked each day from 60 to 57 and in the other group from 60 to 55. You wouldn't expect to see much difference in the rates of lung cancer in these two groups. In other words, they didn't test the hypothesis.
It's hard to quit smoking, but people who quit experience a lot of benefits. Within two years of quitting, your risk of having a heart attack goes down almost as much as if you never smoked.
As everyone knows, it's not easy to make changes in our diet and lifestyle. However, we need to distinguish what's true from what's easy. In the Women's Health Initiative study, the risk of a heart attack and breast cancer was reduced in the subgroup of women who made the most changes in their diet.
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