Chewing the Low-Fat Results
Recent news reports might leave you wondering whether low-fat eating is about to go the way of the once popular low-carb approach.
Many stories have noted that the Women's Health Initiative study -- whose latest findings were published last week in the Journal of the American Medical Association -- has concluded that low-fat diets offered little protection against heart attacks, stroke, and breast and colon cancer. The nearly 50,000 women in the federally funded study were ages 50 to 79 years and had an average body mass index of 29, qualifying them as overweight and nearly obese. Their age and weight also placed them at increased risk for heart disease, stroke and some types of cancer.
"It would be a huge misinterpretation to believe that it doesn't matter what we eat to prevent heart disease and cancer," says Walter Willett, professor of epidemiology and nutrition at the Harvard School of Public Health.
In fact, the study's authors underscore that their findings are "not a test" of the current federal dietary guidelines, which encourage eating a "plant-based, high-fiber diet rich in vegetables, fruits, whole grains, nuts, beans, low-fat dairy" and such healthy fat as nuts, fish, olive and canola oil. Nor did the study evaluate the benefits of regular physical activity, since exercise wasn't part of the trial either. The study addressed the narrower question of whether simply reducing fat intake cuts disease risk.
What the findings do show, yet was often lost in news reports, is that eating more fruit and vegetables as well as less saturated and trans fats cuts the risk of heart disease and cancer. That evidence is "quite strong," Willett says.
But what about body weight? Does a lower-fat approach help reduce it?
The same long-running study provided some answers in January in a report also published in JAMA. Those results showed a direct link between fat intake and body weight. During the first year of the study, the nearly 20,000 women who reduced their average fat intake to about 25 percent of daily calories shed four more pounds than their counterparts who ate about 33 percent of daily calories as fat.
Over the next seven years of the study, fat intake rose slightly in both groups and so did weight. By the end of the study, there was no statistical difference in body weight between the two groups. But as researchers parsed the details, they also found that that women in both groups who ate less fat achieved the greatest overall weight loss and maintained a lower body weight than those who ate more fat.
Even so, "fat is only part of the story," as physician and low-fat proponent Dean Ornish wrote in Newsweek in response to the latest WHI findings. "What we include in our diets is at least as important as what we exclude."
While the WHI study only included women, experts say there's plenty of similar evidence to suggest that the lower fat approach helps men, too. Here are some other key messages from the study:
Control the amount as well as the type of fat eaten. All fat intake decreased in WHI. So participants missed the nutritional benefits of eating nuts, fish and olive oil. Since 2000, the U.S. Dietary Guidelines, the American Heart Association and the National Academy of Sciences have recommended adding small amounts of healthy fat, including two servings of fish per week. Keep saturated fat to 10 percent or less of total calories -- 7 percent if you already have evidence of heart disease or diabetes -- and keep trans fats as low as possible.
"You don't want to take meat out of the diet and add Wonder Bread or Snackwells," says Alice Lichtenstein, professor of nutrition at Tufts University and chair of the American Heart Association's Nutrition Committee. "What you want to do is add things like soy burgers in place of hamburgers and use canola and soybean oil on your salads."
Stick with healthy habits. For the first year, the low-fat group received monthly personal instruction on how to reduce fat intake, then met quarterly for the rest of the study for nutrition help. Yet despite that assistance, the low-fat participants never achieved the study's goals for fat consumption. The first year, the low-fat group cut their fat intake from 37 percent to 24 percent of total calories. (A control group went from 37 percent to 35 percent of calories.) By year six, the low-fat group ate 29 percent of calories as fat -- a moderate level of fat recommended in the 2005 U.S. Dietary Guidelines as well by the American Heart Association and the National Academy of Sciences. (The comparison group's intake rose even more, to 37 percent of calories -- the same amount that both groups ate when the study began.)
Even "bad" carbs aren't so bad. Experts have long debated if too many carbs, especially the refined varieties high in sugar and processed flour, might increase risk of diabetes, weight gain and heart disease. WHI participants in both groups ate mostly refined carbohydrates, averaging four to five servings per day. They consumed only about one serving daily of whole grains. Yet neither group showed increases in blood sugar, changes in insulin, decreases in protective cholesterol or unhealthy blood fats known as trigylcerides. The findings "stress the point that a high carbohydrate diet did not cause weight gain, diabetes or heart disease," says Robert Eckel, president of the American Heart Association.
Don't forget physical activity "We know that there is a lot of evidence that physical activity protects against cardiovascular disease, diabetes and improves weight maintenance," says Penny Kris-Etherton, professor of nutrition at Penn State and a member of the 2005 Dietary Guidelines Advisory Committee. "Yet exercise was not a big part of this study." ·
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