January 20, 2019
Breast Cancer: The Big Fat Question

Breast Cancer: The Big Fat Question

by Berkeley Wellness  

Does dietary fat play a role in breast cancer? Despite many studies, the answer is still unresolved, with most showing little or no association between fat intake in adulthood and breast cancer. But could it be that the timing in life of the fat intake, as well as the type of fat, is what matters? A study pub­lished in Cancer Epidemiology, Biomarkers & Prevention offers some possible answers.

Researchers from the University of Maryland School of Medicine and other institutions followed up on 177 women, ages 25 to 29, who had participated in the Dietary Intervention Study in Children when they were 10 to 18 years old. Those who had the highest intake of saturated fat during that earlier period had higher breast density as adults, as measured by MRI. And dense breasts—which have more glandular and connective tissue relative to fatty tis­sue—are a risk factor for breast cancer. In contrast, a higher intake of mono- and polyunsaturated fats was associated with lower breast density. Other factors that may contribute to breast cancer, including race, education, smoking, and hormone use, were controlled for in the study.

As the researchers explained, "Adoles­cence is a critical period when mammary ducts elongate and branch. These structural changes accompany rapid proliferation of undifferentiated cells, which may render breasts particularly vulnerable to any effects of fat." And the opposite associations of saturated and unsaturated fats with breast density "may reflect different roles of these fats in formation and maintenance of breast tissue." That is, what girls eat during ado­lescence appears to influence breast tissue—and thus later breast cancer risk—more than what they eat as adults. Saturated fats are found predominantly in animal foods, like meat and dairy, while unsaturated fats are found primarily in plant foods, like vegetable oils, fatty fish, nuts, seeds, and avocados.

The study did not look at whether the women who had the highest saturated fat intake as teens were more likely to develop actual breast cancer, but other studies have shown that women with dense breasts have at least a three times greater risk than women with nondense breasts. And the greater the density, the greater the risk.

More support for the idea that timing of diet matters for breast health comes from another study, in BMJ, which followed more than 90,000 female nurses, ages 25 to 42, over 22 years. About half of them reported what they ate during high school, when they were 13 to 18 years old. High fruit intake during adolescence—but not during early adulthood—was associ­ated with a 25 percent lower risk of breast cancer. Despite some inconsistent results (not all fruits were protective, for example), along with inherent limitations of research that relies on participants' self-reports of dietary intake, the overall findings "are in line with the hypothesis that breast tissue is more vulnerable to carcinogenic expo­sure in earlier life than later," the paper concluded.

Both studies included mostly white women, which means the results might not generalize to all women—though, as the BMJ researchers wrote, "it is unlikely that the biology underlying these associations differs by race or education."

Also see Dense Breasts and Cancer.