Low-Fat, High-Fruit Diet Might Not Stop Disease
Published March 2006
You've heard for years that a low-fat diet is good for your health. But does it really reduce your risk of certain diseases? Not according to a recent study.
UC researchers and colleagues at 40 U.S. sites followed nearly 49,000 postmenopausal women (aged 50 to 79) for eight years. Some were asked to eat a diet low in fat and high in fruits, vegetables and whole grains. Others were told to continue eating their normal diet.
The researchers hoped to notice a decrease in the risk of getting cancer and heart disease in the group of women following the low-fat diet.
What they found surprised them, says Margery Gass, MD, professor of obstetrics and gynecology and principal investigator for UC's contribution to the study. Although the women following the low-fat diet reduced their rate of breast cancer by 9 percent, the decrease was not statistically significant. Those assigned to a low-fat diet had the same rates of colon cancer, heart attack and stroke as those who ate whatever they pleased.
The low-fat diet group did report fewer colon polyps, but that didn't translate into lower colorectal cancer rates in the eight years of the study.
Both groups started out with 37 percent of daily calories from fat. Women on the low-fat diets (about 20,000) reduced the percentage of fat in their diets to 24 percent in the first year and to 29 percent by the end of the study.
Women on the low-fat diets participated in 18 small-group sessions with a nutritionist during the first year, and in four sessions a year after that. They engaged in activities designed to help keep them motivated, including potlucks and the development of a cookbook with low-fat recipes.
"We asked the low-fat-diet participants to aim for just 20 percent of their calories from fat," says Dr. Gass. "The women worked very hard to change their eating patterns.
"That's another reason the findings are disappointing," she adds. "We really hoped the dietary modification would produce a major benefit in their health."
There was minimal weight loss on the dietary intervention. Even though it was not a goal of the study, the lack of weight loss may partially explain the absence of cardiovascular benefit.
The study, the largest of its kind, is part of the National Institutes of Health Women's Health Initiative (WHI), a landmark, 15-year study of postmenopausal women's health, including the effects of calcium and vitamin D supplements, hormone therapy and dietary modification.
Janice Shavers-Calloway, of Hollydale in Springfield Township, was one of 3,600 local women who participated in the study.
"I think it was worthwhile, regardless of the findings," she says. "The nutritionist taught us how to cook with different seasonings and olive oil, and that has made me a better, healthier cook."
Calloway, 67, says that while she has not lost any weight, she has maintained her weight and continues to follow a low-fat diet.
"I'm not on any medications and I feel that I'm in pretty good health. I think a lot of that has to do with the low-fat diet," she says.
Although the study suggests a low-fat diet did not lower health risks, Dr. Gass cautions that a diet with less saturated and trans fat and more grains, fruits and vegetables continues to be part of a healthy lifestyle.
"The investigators still believe that lower fat intake is preferable, but clearly one can't focus on total fat alone as was thought in 1991 when the trial was designed," says Dr. Gass. "Low saturated fat intake, exercise, normal weight, not smoking and other factors contributing to a healthy lifestyle all play a role."We're hopeful that as we follow these women another five years we'll see the reduction in breast cancer and colon polyps pay bigger dividends."