Low-fat diet may not reduce cancer and heart risks

By Shaoni Bhattacharya Eating a low-fat diet with plenty of fibre does not reduce the risk of certain cancers and heart disease in postmenopausal women, suggest three major new studies. But many experts are unconvinced by the research, asserting there are weaknesses in its design, and stressing the many studies which back the importance of a low-fat, healthy diet in preventing cancer and cardiovascular disease. The three related studies followed 50,000 women from the Women’s Health Initiative trial over 8 years. No statistically significant difference was seen in the rates of breast cancer, colorectal cancer or cardiovascular disease between women on a reduced fat diet – eating five portions of fruit and vegetables and six portions of grains each day – compared with those who made no dietary changes. “Evidence from this study, along with that from polyp prevention trials, strongly suggests that lowering dietary fat intake and increasing fruit, vegetable and fibre intake in mid-to-late life cannot be expected to reduce the risk of colorectal cancer in this length of time,” writes one research team led by Shirley Beresford at the University of Washington, Seattle, US. The breast cancer study did find a reduced risk with a low-fat, high fibre diet, but this finding was not statistically significant. Its authors say this suggests that if the diet was eaten for longer than eight years the reduction in risk could become significant. The length of the study was one of the study features criticised by others. “Eight years of follow-up is too short a time to show an effect,” Michael Fine, from Rhode Island Hospital, told ABC News. “Let’s wait for 15 to 30 years of follow-up before we judge significance.” Other experts say that the amount of fat cut in the diet was not enough. “It is easy to identify a number of important reasons why this study did not agree with previous research,” Judy O’Sullivan at the British Heart Foundation told the BBC. The diet “didn’t reflect current advice for good heart health, such as salt reduction, increasing intake of good fats such as those in oily fish, and increasing exercise”. O’Sullivan added: “Most of the women in the study were overweight or obese, which increases your risk of developing diabetes – another risk factor for heart disease.” Journal reference: Journal of the American Medical Association (vol 295, p 629, p 643,
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