The most common forms of breast cancer are fueled by estrogen. This explains why being overweight or obese has been found to increase breast cancer risk, especially for women after menopause. This is because after menopause (when the ovaries stop making estrogen), most of a woman's estrogen comes from fat tissue.
Lose Weight = Lower Risk
Studies have shown that losing just 5% or more of your body weight can reduce your risk for the most common estrogen-sensitive breast cancers by 25-50%.
A new study took the research one step further to understand how weight loss through exercise, diet or both affects estrogen levels in the body.
The researchers randomly assigned 439 women who were overweight or obese to one of four groups. One group engaged in moderate exercise (mostly walking), one group dieted, one group did both and one group did neither. All of the women were between the ages of 50 to 75 with an average age of 58.
Those who dieted or dieted and exercised lost an average of about 10 percent of their weight. In addition, they lowered the levels of several hormones. Exercise alone did not produce much of a change in weight or estrogen.
The greatest effect on weight and estrogen levels was through diet plus exercise.
Other factors related to weight may affect the risk of breast cancer. For example, the risk appears to increase for women who gained weight as an adult but not among those who have been overweight since childhood.
Also, excess fat in the waist area may affect risk more than the same amount of fat in the hips and thighs. Researchers believe that fat cells in various parts of the body have subtle differences that may explain this.
American Cancer Society