Nutrition researchers used to think that a high-fat diet increased the risk of breast cancer. However, it now seems the high-fat diet/breast cancer link is not as clear-cut as we had once thought.
Scientists became interested in the link between fat intake and breast cancer when they noticed that women in countries where diets were low in fat had much lower rates of breast cancer than women in countries with higher-fat diets. It has been hypothesized that dietary fat may increase breast cancer risk by affecting estrogen metabolism. Studies have found that vegetarian women who follow a low-fat, high-fiber diet have lower levels of estrogen and less breast cancer. A high-fat diet may also lead to breast cancer by promoting weight gain and body fat accumulation, which in turn increases the risk of breast cancer.
Most large studies have failed to show a strong relationship between total fat intake and breast cancer risk. A recent 14-year study of 89,000 women found no evidence that a high-fat diet promoted breast cancer, or that a low-fat diet protected against it. It is possible that women in these studies didn’t reduce their fat intake enough to see a benefit. The current recommendation of “no more than 30 percent of your daily calories from fat” might be too high to offer protection from breast cancer.
A large Canadian study is underway to determine if a very low-fat diet can prevent breast cancer. So far, one report from this trial found that women who ate a 21 percent fat diet for two years had significantly reduced dense breast areas seen by mammogram (dense breast areas are a risk factor for cancer), compared to women on a 30 percent fat diet.2 Another report from this research group revealed that women who followed a 15 percent fat diet for two years had lower levels of circulating estrogen, which could offer protection over the long term. Based on these initial reports,
I do believe that following a low-fat diet is a wise precautionary measure.