Curbing Cancer? Low-Fat Diet During Adolescence Cuts Hormones, Possibly Breast Cancer Risk

Cutting back on cheeseburgers and French fries could spare girls more than extra pounds. A low-fat diet also reduces young girls’ sex hormone concentrations, a new study finds. What’s more, researchers say, the adolescent drop in hormones that are known to spur breast cancer in adults might stave off the disease later in life. More work is required to confirm the connection, however.

Scientists have suspected that fatty foods might spur breast cancer, but the evidence remains inconclusive. In countries where people traditionally eat less fat, breast cancer rates are lower than in countries with higher-fat diets, says epidemiologist Joanne F. Dorgan at the Fox Chase Cancer Center in Philadelphia. Furthermore, when Asian people immigrate to the United States and begin eating fattier foods, their odds of getting breast cancer skyrocket. However, some studies of women in the United States have failed to link dietary habits to breast cancer.

Dorgan thought that low-fat eating might have its greatest impact on breast cancer risk during adolescence because that’s when breast tissue forms. To uncover diet’s role in girls’ pubescent hormone levels, Dorgan and her colleagues took advantage of the Dietary Intervention Study in Children–a clinical trial sponsored by the National Heart, Lung, and Blood Institute that’s testing the safety and effectiveness of a low-fat diet for lowering blood cholesterol in children with high concentrations. In 1990, the team initiated an ancillary study of the children’s sex hormones.

Cutting the fat

Nearly 300 girls, 8 to 10 years old, were randomly assigned to a low-fat dietary intervention group, in which 28 percent or fewer of their calories came from fat, or to a group whose diet wasn’t restricted. The researchers measured sex hormone concentrations in the blood after 1, 3, 5 and 7 years in the trial.

After 5 years, the girls eating less fat had lower concentrations of four variants of the hormone estrogen during the first half of their menstrual cycles. Estrogen has been linked to breast cancer in adults. The girls also had higher concentrations of testosterone, a hormone that confers male characteristics in men but also turns up at low concentrations in women. After 7 years, the researchers saw no differences in estrogen or testosterone concentrations, but the girls on the low-fat diet had half the progesterone–another female sex hormone–of girls with an unrestricted diet. This difference showed up during the second half of their menstrual cycles. The findings are reported in the Jan. 15 Journal of the National Cancer Institute.

“The differences in hormones came with a modest difference in dietary intake and without any apparent effect on the girls’ progression through maturity,” Dorgan says. “We expected to see some hormonal differences, but we were surprised at their magnitude.”

Whether the effects of diet on sex hormones will translate into reduced breast cancer risk for the girls, “we still don’t know,” Dorgan adds. The team plans to conduct a follow-up study of the girls–now women in their 20s.

Encouraging news for fighting breast cancer

Neal D. Barnard, nutrition researcher and founder of the Physicians Committee for Responsible Research in Washington, D.C., finds the results encouraging. “It’s known that a low-fat diet can modify hormones in adults, but this study was done at precisely the time when a hormonal change might affect breast cancer risk the most,” he says.

Although the researchers didn’t observe delayed maturation in the girls on the low-fat diet, they propose that a subtle delay might result from reduced hormone concentrations. Epidemiologist Paolo G. Toniolo of the New York University School of Medicine in New York City adds that the results raise “the possibility that even a slight change in girls’ diets could slow down maturation,” a factor known to contribute to breast cancer.

The results are “interesting and suggestive” that diet might influence girls’ hormone concentrations, says epidemiologist Michelle D. Holmes of Harvard Medical School and Brigham and Women’s Hospital in Boston. But, she cautions, no one can yet say whether the changes seen in the girls will curb breast cancer in their future.