Roughly one-tenth of postmenopausal breast cancers are linked to high body mass index (BMI)—a measure of excess body fat. However, BMI is unreliable, especially in older women, because it doesn’t account for age, sex, or ethnicity. Using newer, more accurate body fat assessments, a recent study predicted that nearly 40% of breast cancers are due to excess body fat.

The study involved 1,033 women with breast cancer and 1,143 women without. Researchers calculated their body fat using BMI and CUN-BAE, a body fat estimator that accounts for age and sex. Then, they calculated the proportion of breast cancer cases linked to body fat.

They found that 23% of postmenopausal breast cancer cases were linked to excess body fat when assessed by BMI, but the estimate jumped to 38% with CUN-BAE. Among women with hormone receptor-positive tumors, CUN-BAE indicated a striking 41.9% of cases were attributable to excess body fat—more than double the 19.9% predicted with BMI.

These findings suggest that using BMI alone underestimates the cancer burden from excess body fat, especially for hormone receptor-positive breast cancer. Approximately 43% of postmenopausal women in the U.S. have obesity, markedly increasing their risk for breast cancer. Sulforaphane, a bioactive compound derived from broccoli, exerts potent anticancer effects. Learn more in this episode featuring Dr. Jed Fahey.