A low-fat diet cuts a woman's chance of developing ovarian cancer by 40 per cent, finds a large-scale U.S. study.

The study "Low-Fat Dietary Pattern and Invasive Cancer Incidence: Further Results from the Women's Health Initiative Dietary Modification Trial," was published Tuesday in the Journal of the National Cancer Institute.

A low-fat diet was one in which fat accounted for only 20 per cent of calories.
(CBC)

The Women's Health Initiative Dietary Modification Trial was conducted in 40 clinical centres across the U.S. and followed 48,835 healthy post-menopausal women for an average of 8.1 years. The average age of the women studied was 62.3 years.

Twenty thousand women in the intervention group were tracked to determine whether a low-fat diet would reduce the risk of cancer.

A low-fat diet was one in which fat accounted for only 20 per cent of calories, replacing calories from fat with calories from vegetables, fruits and grains.

The women in this group were counselled to decrease their fat intake in 18 group sessions in the first year and quarterly maintenance sessions thereafter.

The 30,000 women in the control group received diet-related education materials only.

Differences show up after four years

At the onset of the study, women in both groups consumed on average 35 per cent of calories from fat. By the end of the first year, the low-fat diet group dropped that percentage to 24 per cent.

By the end of the study, that percentage had increased to 29 per cent, but the control group's percentage of calories from fat also rose to 37 per cent. As well, the low-fat group consumed more vegetables, fruits and grains.

Scientists discovered that those women who had the highest fat intake at the beginning of the study and who lowered it the most had the lowest risk of ovarian cancer.

The absolute incidence rates in the first four years showed little difference, with 0.52 cases per 1,000 people in the intervention group and 0.45 cases per 1,000 people in the control group. But the rates in the subsequent years were considerably different, with 0.38 cases per 1,000 in the intervention group and 0.64 cases per 1,000 in the control group, a difference of about 40 per cent.

"Although there was little evidence for an intervention effect on ovarian cancer risk during the first few intervention years, a stronger and nominally statistically significant risk reduction emerged in later years," reads the study.

According to the Canadian Cancer Society, 2,300 cases of ovarian cancer and 1,600 deaths from the disease were estimated to have occurred in 2006.