A low-fat diet may protect women from ovarian cancer, concludes a study of more than 40,000 older women that provides the first evidence that diet has an effect against the disease.
Those who followed a low-fat diet for eight years cut their chances of ovarian cancer by 40 per cent, researchers reported in the Journal of the National Cancer Institute. But it took four years for the low-fat diet to have any effect.
Researchers tracked almost 49,000 post-menopausal women from around the United States for about eight years as part of the mammoth Women's Health Initiative study, which enrolled tens of thousands of healthy women ages 50 to 79 to track several leading killers.
About 40 per cent of the women were asked to lower the amount of fat in their diet to about 20 per cent of calories, from an average of 35 per cent. The others were asked to eat their usual diet.
No difference was seen in ovarian cancer risk in the first four years of the study. But in the final four years, the women who ate a diet lower in fat were 40 per cent less likely to develop the cancer than the other group of women.
Until now, the only known lifestyle prescription against ovarian cancer was to use birth control pills. Taking the pills for five years can lower the cancer risk by up to 60 per cent, and that protection lingers years after pill use ends.
The new findings now offer an option for postmenopausal women to try as well.
Ovarian cancer is fairly rare; about 2,400 new cases of ovarian cancer are diagnosed in Canada every year compared to an estimated 22,300 new cases of breast cancer diagnosed each year. But because it is often detected only after it has spread throughout the abdomen, only 45 per cent of patients survive five years.
Ovarian cancer can strike anytime in adulthood, but risk increases with age. Mutations in the so-called breast cancer genes BRCA1 and BRCA2 also increase the risk of ovarian cancer.
The theory of how fat intake would affect ovarian cancer risk is the same theory about why obesity affects the risk for breast cancer: the extra fat increases the amount of estrogen circulating in the blood, which may in turn overstimulate the ovaries and the breasts.
The study, though, found that the low-fat diet had little impact on rates of breast cancer, nor on colorectal cancer and heart disease rates.
There are a number of theories of why that is. The women may have started healthier eating too late; the average age of the women at the start of the study was 62. Or it may be because most of the women were overweight, a major risk factor for many cancers and heart disease, and the diet wasn't designed to shed pounds.
Or it's possible that many of the women were not able to adequately maintain the low-fat diet for the entire eight years. Most of the dieters cut their fat intake to 24 per cent of calories, not quite as much as recommended. Over time, the fat crept back: after eight years, they were up to 29 per cent - though that is still lower than the average American diet, which contains an average of 35 per cent fat.
Many of the women who took part in the study are still being tracked for an additional five years, so new findings may yet emerge.
