Reducing dietary fat doesn’t cut disease risk: study

CHICAGO - Women who ate less fat and more fruits, vegetables and grains did not reduce their risk of two types of cancer or heart disease, though they did show signs of being healthier, researchers said on Tuesday.

The broad conclusion of the study - that a healthier diet doesn’t ward off disease - drew criticisms from some experts who said it could be misinterpreted and taken as an excuse by some people to eat as much of anything they want.

Editorials accompanying the three related studies published in the Journal of the American Medical Association pointed to the relatively healthy population of women in the study, and noted the women who modified their diets might have cut out fats found in fish and nuts now known to be healthy components of the “Mediterranean diet.”

Caution

“I encourage people to interpret this with caution because we have many unanswered questions,” Dr. Jeanette Keith of the University of Chicago said in a phone interview. She was not part of the study.

Other outside experts described the large, multimillion-dollar, government-funded study as the most definitive to date, upending widely held beliefs that people can avoid disease by eating healthier foods.

The same Women’s Health Initiative study previously drew the surprising conclusion that hormone-replacement therapy carries heightened risks of health ailments such as stroke.

“This large randomized clinical trial provides the most definitive evidence to date of the impact of a low-fat diet,” said Dr. Michael Thun of the American Cancer Society.

But Thun cautioned that proponents of low-fat diets could also draw positives from the findings.

Early stages

The women on healthier diets did suffer 9 percent few cases of invasive breast cancer - considered statistically insignificant - and had 15 percent less estradiol in their blood, a form of estrogen that raises the risk of breast cancer. And they had 9 percent fewer self-reported colon polyps, which are precursors of colon cancer.

“It is important to remember that cancers often take decades to develop, and we may only be seeing the early stages of the impact of a low-fat diet intervention on the risk of colorectal cancer and other diseases,” said study author Shirley Beresford of the Fred Hutchinson Cancer Research Center in Seattle.

Nearly 20,000 of the 49,000 women participants, aged 50 to 79, were instructed to reduce dietary fat and to eat at least five servings of fruits and vegetables daily and six or more servings of grains. After being followed for a little more than eight years, they missed the goal of consuming 20 percent of their calories as fat, instead consuming 29 percent as fat compared to 37 percent among those who did not change diets.

The small difference in fat intake was evident in the narrow gap in body weight between the two groups, Dr. Keith said. In addition, if the women cut out fatty dairy products they may have reduced their intake of calcium and Vitamin D, both nutrients known to reduce colon cancer risk, she said.

‘An integrated lifestyle program needed’

The impact of a better diet on indicators for heart disease was mixed, with only slightly lower levels of so-called bad cholesterol but similar levels of good cholesterol, triglycerides, glucose and insulin in both groups of women.

Dr. Robert Eckel, president of the American Heart Association, said diet was just one element of “an integrated lifestyle program” that should include exercise.

“Just switching to low-fat foods is not likely to yield much health benefit in most women. Rather than trying to eat ’low-fat,’ women should focus on reducing saturated fats and trans fats,” said Marcia Stefanick of the Stanford Prevention Research Center in California, who oversaw the study.  

Reuters

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