Fat, Fiber, and Breast Cancer Risk

Long-term Diet Changes may Decrease Breast Cancer

Medically Reviewed by Michael W. Smith, MD on September 22, 2003
From the WebMD Archives

Sept. 22, 2003 -- Investment advisors know it's true: Start investing when you're young to get a big payoff later on. The same applies to healthy eating -- and it could even cut a woman's breast cancer risk in midlife, a new study shows.

In the current issue of Cancer, the study looks at a link between diet and breast cancer risk. Researchers have long suspected a link, but other factors involved in breast cancer's origins have complicated the picture.

The proposed theory is that prolonged exposure to increased estrogen and progesterone levels in the body increases breast cancer risk, says researcher Peter H. Gann, MD, preventive medicine specialist at Feinberg School of Medicine at Northwestern University in Chicago.

And a healthy low-fat, high-fiber diet has long been suspected of lowering these hormone levels.

Chipping Away at Estrogen

In this newest study, a pattern of small changes in estrogen levels emerges -- changes due to diet -- which could chip away at estrogen levels over time, reports Gann.

The findings are an important addition to the puzzle of breast cancer risk, Michele R. Forman, PhD, a National Cancer Institute researcher, writes in an accompanying editorial.

In the study, 213 women -- all between 20 and 40 years old -- were asked to eat either a high-fiber, low-fat diet, or their usual diet. The women also tested their own urine at assigned times every month to provide researchers a measure of estrogen and progesterone hormones circulating in the bloodstream.

One year later: estrogen levels were very similar between the two groups, reports Gann. When the women's age and body mass index (an indicator of body fat) were factored in, Gann saw only small differences in daily estrogen levels between the two groups.

However, over the year's time, all of this healthy eating had a noticeable cumulative effect. The "healthy diet group" had an 8% reduction in estrogen levels; the "regular diet" group had less than a 1% drop, Gann reports.

Over several decades' time, these small reductions could make a significant difference in breast cancer risk, he writes.

Diet + Exercise + Weight Control

In her editorial, Forman notes that other studies have pointed to a range of reductions in estrogen levels -- from 6% to 36%.

Gann suggests that researchers now need to explore the effects of dietary changes on other hormones that may affect breast cancer risk -- such as leptin (hormone linked to obesity), growth hormones, and insulin.

Gann says that it's still unknown whether concentrating on weight loss rather than a low-fat diet might produce a more significant drop in hormone levels -- and potentially breast cancer risk.

In the end, it comes to this: Diet, weight control, and physical activity are all likely to play a role in reducing breast cancer risk, Forman explains. "We doubt ... one best approach is likely to be found," she writes.