Many of you who have heard me talk over the last few years have heard me say that the best way to prevent breast cancer and decrease recurrence is the combination of exercise and maintaining a healthy weight. I always feel a bit guilty telling women to lose weight, because I know first-hand how hard it is! Nonetheless, it keeps coming up in the research and there is no question in my mind that by tackling the obesity epidemic in our country we will decrease breast cancer risk.
The most recent evidence comes from the Nutrition and Exercise for Women study, the first randomized controlled trial to test the effects of weight loss and exercise on sex hormones that are biomarkers for breast cancer risk.
The study enrolled 439 overweight postmenopausal women who participated in less than 100 minutes of exercise a week. They were divided into four groups: a calorie-reduced diet group, an aerobic exercise group, an aerobic exercise and calorie-reduced diet group, and a control group.
The goal for the women on the reduced diet was a 10 percent reduction in body weight by six months that was maintained through the 12-month trial. The goal for the women who exercised was 45 minutes or more of moderate-to-vigorous aerobic exercise (consisting primarily of brisk walking) five days a week. The women in the control group were asked not to change their diet or exercise habits during the course of the study.
At the beginning and at the end of the study, the researchers measured the blood levels of the sex hormones estrone, estradiol, free estradiol, total testosterone, free testosterone, and adrostenedione along with the level of sex hormone-binding globulin (SHBG, which reduces the hormones bioactivity). High levels of these sex hormones have been shown to be associated with breast cancer risk.
The study found that the women who lost weight, with or without exercise, had the largest decrease in their levels of estrone estradiol, free estradiol and free testosterone and increased in their level of SHBG. Based on past studies, these findings suggest that the decrease in these sex hormones reduced these womens breast cancer risk by as much as 22 percent. (This reduction in hormone levels helps explain why weight loss after a breast cancer diagnosis also appears to reduce the risk of recurrence.)
Why do I think this study is important? At every talk I give, someone asks about a recent article they read or advertisement they saw that suggests that eating a certain food be it blueberries, pomegranates, or coconut water will reduce their breast cancer risk. It is much less common for me to get a question about weight loss. But what the research is telling us is this: the best thing you can do to reduce your breast cancer risk is reduce the calories you eat and get off of the couch and out of your slippers and into your sneakers and on the streets.
As much as we would like a magic food to prevent breast cancer, it is weight that is critical as well as exercise! Especially when we are postmenopausal, we need to get moving!