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Women who are obese when diagnosed with breast cancer are more likely to experience disease recurrence and more likely to die from the disease, according to the results of a study published in Cancer.1

Breast cancer is the most commonly diagnosed type of cancer (other than skin cancer) in U.S. women. Each year, roughly 250,000 women are diagnosed with breast cancer and close to 40,000 die of the disease. Obesity has been associated with an increased risk of developing breast cancer and has also been found to hinder treatment.2

The majority of breast cancers are hormone receptor-positive, meaning they are stimulated to grow by the circulating female hormones estrogen and/or progesterone. Unfortunately, the same hormones that fuel tumor growth are also elevated in obese women—which could, in part, explain the relationship between obesity and breast cancer. Research is ongoing to evaluate this relationship in order to improve prevention and treatment strategies.

Research suggests that losing weight through a healthy diet and exercise program significantly lowers blood estrogen levels in postmenopausal women. Losing weight—even just a moderate amount—can significantly reduce the levels of circulating estrogen in the body, thereby reducing the risk of breast cancer and the chance of recurrence following treatment for breast cancer.3

Researchers at the Fred Hutchinson Cancer Research Center performed the first randomized, controlled clinical trial to evaluate the effects of weight loss on sex hormones in overweight and obese post-menopausal women. The study included data from 439 overweight-to-obese, sedentary women ages 50 to 75 from the Seattle area. The women were randomly assigned to one of four groups: exercise only, diet only, exercise plus diet, or no intervention. At the end of the study period, the women in the diet only and diet plus exercise groups lost an average of 10 percent of their starting weight.

The researchers then measured the effects of this weight loss on the blood levels of several types of sex hormones, including three forms of estrogen; two types of testosterone; androstenedione, a steroid necessary for the production of sex hormones; and sex hormone binding globulin, or SHBG, a protein that binds to sex hormones and therefore makes them less biologically active.

At the end of the study, the researchers found significant reductions in hormone levels among women who lost weight, with the biggest reduction among those who were in the diet plus exercise group.

High levels of SHBG are associated with reduced breast cancer risk, whereas high levels of estrogen (estrone, estradiol, and free-estradiol) are associated with an increased risk. In the diet plus exercise group, estrone levels decreased 11.1%, estradiol levels decreased 20.3%, free estradiol levels decreased 26%, and SHGBF levels increased 25.8%. In the diet only group, estrone levels decreased 9.6%, estradiol levels decreased 16.2%, free estradiol levels decreased 21.4%, and SHGBF levels increased 22.4%.

The amount of weight lost impacted the changes in hormone levels. Losing as little as 5% of one’s total body weight had a beneficial impact on hormone levels, and the effect increased with the amount of weight lost. The biggest effect was seen in the diet plus exercise group.

Doctors from the Eastern Cooperative Oncology Group (ECOG) have also examined the relationship between body mass index (BMI) and breast cancer outcomes in nearly 5,000 women with stages I, II, and III breast cancer who were given standard chemotherapy treatment. About one-third of the women were obese and one-third were overweight.

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Over a period of eight years, one in four women experienced a cancer recurrence and 891 died, including 695 from breast cancer. The researchers found that obese women were 40% more likely to experience cancer recurrence and 69% more likely to die from breast cancer or any other cause when compared to women of normal weight. Among women who were overweight, but not obese, there was a general trend toward increased risk of recurrence and death with increasing weight. The link was especially pronounced for women with estrogen receptor-positive breast cancer.4,5

Can Losing Weight Make a Difference?

The American Institute for Cancer Research and the World Cancer Research Fund International convened a 21-member board to evaluate risks of cancer. The board reviewed data from over 7,000 published studies and reported the following:

  • ­ Obesity significantly increases the risk of six cancers: colon, kidney, pancreas, esophagus, and endometrial and breast cancer in postmenopausal women.
  • ­ Even a few excess pounds or increased abdominal girth results in increased risks.
  • ­ Increased intake of red meat increased the risk of cancer by 15%.
  • ­ Increased intake of processed meats increased the risk of colorectal cancer.

According to the results found by this analysis, the researchers made the following recommendations for the prevention of cancer as related to weight:

  • ­ Remain as lean as possible within the normal range of weight.
  • ­ Eat a diet based on food derived from plants (fruits, vegetables, whole grains and legumes).
  • ­ Avoid more than 18 ounces of red meat per week.
  • ­ Avoid as much processed meat as possible.
  • ­ Remain physically active.
  • ­ Nutritional needs should be met, as much as possible, through diet alone.
  • ­ Consumption of empty-calorie foods, such as sugary drinks, should be limited.
  • ­ Breastfeeding should be considered over formula.
  • ­ Consumption of salt, moldy grains or moldy legumes should be limited.
  • ­ Alcohol intake should be limited.
  • ­ Survivors of cancer should follow these same recommendations.

The researchers stated that physicians should begin weight loss intervention at the earliest signs of their patients gaining weight or being overweight. As well, physicians should be discussing diet and physical activity with their patients.

Individuals who are overweight may wish to speak with their physician regarding a weight loss and physical activity program to greatly reduce their risk of developing cancer.


  1. Campbell KL, Foster-Schubert KE, Alfano CM, et al. Reduced-calorie dietary weight loss, exercise, and sex hormones in postmenopausal women: Randomized controlled trial. Journal of Clinical Oncology. Published early online May 21, 2012. doi: 10.1200/JCO.2011.37.9792
  2. Sparana JA, Wang M, Zhao F, et al. Obesity at diagnosis is associated with inferior outcomes in hormone receptor-positive operable breast cancer. Cancer. Published early online August 27, 2012. DOI: 10.1002/cncr.27527
  3. Folkerd EJ, Dixon JM, Renshaw L, et al. Suppression of plasma estrogen levels by letrozole and anastrozole is related to body mass index in patients with breast cancer. Journal of Clinical Oncology. Published early online July 16, 2012. doi: 10.1200/JCO.2012.42.0273
  4. Ewertz M. Effect of obesity on prognosis after early breast cancer. Presented at the 32nd CTRC-AACR San Antonio Breast Cancer Symposium. December 9-13, 2009. San Antonio, TX. Abstract 18.
  5. Anderson PR, Freedman G, Hanlon A, et al. Obesity at Diagnosis confers Worse Outcome in Patients with Early Stage Breast Cancer Treated with Breast Conservation Therapy. Proceedings from the 46th annual meeting of the American Society of Therapeutic Radiology and Oncology held in Atlanta GA, Oct 2-7, 2004; Abstract #132.
  6. Cancer, Vol. 92, No. 4, pp. 720-729, 2001
  7. Campbell KL, Foster-Schubert KE, Alfano CM, et al. Reduced-calorie dietary weight loss, exercise, and sex hormones in postmenopausal women: Randomized controlled trial. Journal of Clinical Oncology. Published early online May 21, 2012. doi: 10.1200/JCO.2011.37.9792
  8. World Cancer Research Fund, American Institute for Cancer Research. Food, Nutrition, Physical Activity, and the Prevention of Cancer: A Global Perspective. 2007. Available at: . Accessed November 2007.

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