Reporting From ASCO: Obesity and Breast Cancer

A study presented this week at the 2014 American Society of Clinical Oncology (ASCO) Annual Meeting suggests that in younger women with early stage estrogen-receptor positive (ER+) breast cancer, obesity is associated with poorer outcomes. The research comes from a review of 70 clinical drug trials enrolling 80,000 women. It further supports an increasing body of data suggesting worse overall outcomes related to breast cancer for women who are overweight or obese compared with women who stay at a healthy weight.

About two-thirds of all breast cancers are hormone receptor positive, meaning estrogen and/or progesterone fuel their growth. Fat cells help make and store hormones including estrogen. Therefore, carrying excess fat tissue may increase breast cancer risk by increasing the body’s exposure to circulating estrogen. Previous research has shown overweight and obesity increase risk for breast cancer development in post-menopausal women, as does weight gain in adulthood. In fact, women who gained 60 pounds after the age of 18 had twice the risk of post-menopausal breast cancer versus women who maintained their same weight. To date, however, negative effects of overweight and obesity with regard to breast cancer were demonstrated only in older women, not pre-menopausal women with ovarian function.

Preventing excess weight gain in the first place is the best way to reduce risk for certain cancers and many other illnesses. It isn’t clear yet whether weight loss in adulthood reduces risk of cancer diagnosis or mortality. However, we do know that even a modest sustained weight loss (5%-10%) in people who are overweight or obese decreases risks for heart disease and diabetes. Given the potential relationships between these types of systemic and metabolic diseases and cancer growth, it is certainly possible that weight reduction could have even more benefits than those we already know.

Many risk factors for breast cancer, such as family history, are not modifiable. The good news is, avoiding excess weight gain – both for women at risk for breast cancer and those already diagnosed with breast cancer – is largely controllable. The following points are helpful in weight reduction and management over time:

  • Choose a mostly plant-based diet with a variety of whole foods.
  • Limit processed foods and fast foods.
  • Decrease added and refined sugars.
  • Monitor portion sizes.
  • Eat mindfully and pay attention to physical hunger and satiety cues.
  • Eat meals more slowly.
  • Keep a written food diary.
  • Engage the support of friends and family.
  • Exercise for at least 30 minutes most days of the week.
  • Get enough sleep.

Meet with a Registered Dietitian Nutritionist (RD/RDN) to discuss a nutrition plan that is personalized, practical, and sustainable over a lifetime. You can find a local RD/RDN who specializes in weight management and/or cancer nutrition at www.eatright.org.

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