Previous reports from the Women's Health Initiative Dietary Modification Randomized Controlled Trial examined the effect of a low-fat diet on the risk of breast and colorectal cancer in postmenopausal women, but it was not yet known whether the same diet would alter ovarian cancer risk.

Ross Prentice, Ph.D., of Fred Hutchison Cancer Research Center in Seattle and colleagues analyzed data from the dietary modification trial to see if the changes in the women's diets decreased the risk of ovarian and endometrial cancer and invasive cancers overall. In the trial, nearly 20,000 women were randomly assigned to the diet modification group and almost 30,000 women ate their normal diet. The women participating in the diet were asked to reduce their fat intake to 20 percent of their overall diet, as well as eat at least five serving of fruits and vegetables a day and at least six servings of whole grains. They were followed for an average of eight years.

The risk of ovarian cancer was similar in the two groups for the first four years of follow-up, but it was reduced in the dieting group during the following four years. Women who had the highest fat intake before the trial saw the greatest reduction in risk. There was no difference in endometrial cancer risk between the two groups, but a trend toward a reduction in invasive cancers overall was suggested in the dieting group. It was not, however, statistically significant.

Ongoing follow-up of trial participants may provide additional valuable assessment of the effects of a low-fat dietary pattern on these and other cancer incidence rates, the authors write.

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"It seems that some people are more susceptible to changes in the environment than others and the explanation for this may be partly genetic. It is important for psychologists, geneticists and biologists to work together to discover the reasons for this."

Dr Lesley Walker, director of cancer information at Cancer Research UK, said: "This research adds to the evidence that the UK is in the grip of an obesity epidemic. We know that high body weight increases the risk of a number of cancers and it is important we get this message out to as many people as possible.

"A healthy diet with plenty of fibre, fruit and vegetables as well as regular exercise can help people to lose weight and reduce their risk of cancer. Cancer Research UK, together with the charity Weight Concern, has devised Ten Top Tips to help people control their weight."

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