BOSTON -- A modest reduction in fat consumption by women is unlikely to cause a substantial decrease in the incidence of breast cancer, researchers said Wednesday.
The finding by a team led by Dr. Walter Willett, associate professor of epidemiology at Harvard Medical School, casts doubt on previous suggestions that dietary fat was a risk factor in breast cancer.
Previously available data on humans was 'sparse and inconsistent,' Willett said.
In 1980, 89,538 U.S. registered nurses who were 34 to 59 years old and had no history of cancer completed a questionnaire designed to measure individual consumption of total fat, saturated fat, linoleic acid and cholesterol, as well as other nutrients, a study in the New England Journal of Medicine said.
Of the total calories women consumed, fat comprised a mean of 44 percent in the highest category to 32 percent in the lowest.
During four years of follow-up, 601 cases of breast cancer were diagnosed among the nurses.
Researchers concluded the relative risk of breast cancer among women in the highest category of total fat consumption was not measurably higher than women in the lowest category.
Results were similar for postmenopausal and premenopausal women.
Willett said the data were based on a limited period of follow-up and did not preclude a possible influence of fat intake before adulthood or at levels lower than 30 percent of calories.
'Our findings suggest, however, that a reduction in total fat intake of approximately 25 percent by women is unlikely to cause a substantial decrease in the incidence of breast cancer,' Willett said.
Commenting on the study, Dr. Robert Hutter, chairman of the department of pathology at St. Barnabas Medical Center in New Jersey and past national president of the American Cancer Society, said, 'I think the conclusion that he has come to ... is obviously a correct conclusion.'
Willett said dietary fat was suspected as a possible cause of breast cancer because of a high correlation between national per capita fat consumption and the incidence of the disease, and because of a number of animal experiments showed consumption of lipids influenced the growth of mammary tumors.
Subsequent recommendations that the U.S. population reduce its fat intake to about 30 percent of total calories were based in part on an anticipated reduction in the incidence of breast cancer, he said.
'The data were indeed very limited and one could argue the conclusions may have been premature.'
Age at first pregnancy and history of breast cancer in relatives are considered more important risk factors for the disease.
Despite his findings, Willett said there are good reasons to limit fat consumption, for example, to prevent coronary heart disease.
His is the largest study ever of women investigating the links between dietary fat and breast cancer.
Willett said the National Institutes of Health recently provided funding to continue his study for seven more years.
The study was conducted at Channing Laboratory of Harvard Medical School and Brigham and Women's Hospital.