Overweight and obese women -- defined as having a BMI (body mass index) higher than 25 -- have a higher risk of being diagnosed with breast cancer compared to women who maintain a healthy weight, especially after menopause. Being overweight also can increase the risk of breast cancer coming back (recurrence) in women who’ve been diagnosed with the disease.
This higher risk is partially because fat cells make estrogen; extra fat cells mean more estrogen in the body and estrogen can make hormone-receptor-positive breast cancers develop and grow. Scientists also have recently found that extra fat cells can trigger long-term, low-grade inflammation in the body. Chronic inflammation has been linked to a higher risk of breast cancer recurrence; the proteins secreted by the immune system seem to stimulate breast cancer cells to grow, especially estrogen-receptor-positive breast cancer in postmenopausal women.
Statistics show that more than 66% of U.S. women are overweight or obese, which puts them at higher risk for breast cancer.
Research has suggested that excess fat in the stomach area, also called belly fat, raises the risk of several conditions, including heart disease, diabetes, and colorectal cancer. But it hasn’t been clear if belly fat was worse than fat in other parts of the body for increasing breast cancer risk.
Part of the way doctors determine breast cancer risk is to look at levels of certain hormones and other proteins in the blood stream. Doctors calls these biomarkers. Higher levels of:
- leptin (the hormone that makes you feel full after you eat)
- inflammatory proteins
are associated with higher breast cancer risk.
Some research has suggested that these biomarkers are mainly produced in belly fat, so doctors wondered if losing belly fat specifically would affect breast cancer risk more than lowering total body fat.
Results from the SHAPE-2 study suggest that reducing total body fat, rather than just belly fat, was better at lowering biomarkers linked to breast cancer risk.
The study was published online on May 16, 2017 by the journal Endocrine-Related Cancer. Read the abstract of “Association between changes in fat distribution and biomarkers for breast cancer.”
The SHAPE-2 study was done in the Netherlands and included 243 overweight, postmenopausal women. None of the women had been diagnosed with breast cancer or any other type of cancer and were considered healthy.
The women were randomly assigned to lose a certain amount of weight -- between 10 and 13 pounds -- through either diet alone or diet and exercise over 16 weeks.
The women were about 60 years old and didn’t exercise. None of the women used hormone replacement therapy and none of them were diagnosed with diabetes.
The researchers measured blood levels of:
- inflammatory markers
both before the study started and at the end of the 16 weeks.
Changes in total body fat and belly fat were measured with x-rays and MRI scans.
After 16 weeks, a decrease in total body fat was associated with lower levels of estrogen, testosterone, and leptin. A decrease in belly fat was associated with a reduction in inflammatory markers.
"It is known that belly fat increases the risk of several chronic diseases, independently of total body fat, but for reducing sex hormone levels total body fat seems more important," said Dr. Evelyn Monninkhof, of the University Medical Center Utrecht and one of the study’s authors. "Although previous research has reported conflicting associations between breast cancer risk and belly fat, this study used a more accurate scanning based method of determining fat distribution, rather than waist circumference. We obtained two measurements of both fat depots and biomarkers over time; and we used more accurate DEXA measurements for total body fat, as well as MRI for belly fat."
Losing weight can be harder as you get older, but it can be done with careful changes to your diet and daily exercise. The first thing to do is talk to your doctor about a healthy weight for you based on your age, height, body type, and activity level. Next, talk to your doctor about a safe and sensible plan to lose weight designed specifically for you and your needs.
For more information on breast cancer risk and weight, as well as steps you can take to lose weight, visit the Breast Cancer Risk Factors: Being Overweight page in the Breastcancer.org Lower Your risk section.