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Overeating, Weight Gain May Promote Breast Tumor Growth

overeating, obesity, breast cancer

Obesity is a risk factor for the development of many types of cancer, including breast cancer. A new study again associates the risk of extra weight with cancer and adds that women may be able to reduce this risk by taking measures to lose weight before menopause hits.

Paul S. MacLean PhD, an associate professor of medicine at the University of Colorado’s Anschutz Health and Wellness Center, and colleagues studied the effects of overeating and obesity on laboratory rats that had surgery to remove their ovaries, thus mimicking menopause. The found that excess weight plus continued overfeeding promoted aggressive tumor growth and progression of cancer.

One reason for the enhanced tumor growth, the scientists found, was that the obese rats were unable to appropriately handle the excess glucose calories which were then taken up by the cancerous breast tissue. The lean rats, on the other hand, stored the excess glucose and fat in the liver, fat and muscle tissues, and in healthy breast tissue.

The tumors in the obese rats also had higher expressions of the progesterone receptor (PR) which was related to higher expressions of genes involved in energy use and proliferation (uncontrolled growth). This pattern of gene expression is often seen in postmenopausal women with PR-positive breast tumors. Obese women with a positive hormone receptor status have been found to have a poorer prognosis than their leaner counterparts.

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"Obese postmenopausal women have increased risk for breast cancer and poorer clinical outcomes compared with postmenopausal women who are lean," said Dr. MacLean. "If our findings in rats translate to humans, it means that the perimenopausal period is a critical window of time for determining breast cancer risk later in life."

Thus, “an obese woman's risk for postmenopausal breast cancer and poor clinical outcome could be reduced by perimenopausal lifestyle modifications, such as restricting food consumption and increasing exercise, and/or perimenopausal use of drugs, such as metformin, to improve metabolic control," the authors conclude.

Overeating – or eating too many calories to maintain weight – is a learned habit. Babies are born knowing to eat when they are hungry and stop when they are full. As we grow older, we overeat for many reasons, such as for comfort or because of a “broken” metabolism process which causes our hunger response to fail. There are ways we can overcome this:

• Eat slowly. Research led by Mark Gold MD at the University of Florida has shown it takes 12 or more minutes for food satisfaction signals to reach the brain of a thin person, but 20 or more minutes for an obese person. Eating slowly ensures that these important messages have time to reach the brain.
• Be aware. Be more attentive about the whole eating experience - don't eat when you are watching television, in front of the computer, or driving. When we're distracted or hurried the food we eat tends not to register well in our brains, so we inadvertently eat more than we need.
• Make the first bites count. Satisfying your taste buds by really savoring those first few bites may help you stop eating when you're physically comfortable.
• Keep up appearances. Using a smaller plate and paying attention to the presentation of a meal can increase your awareness of the food in front of you and help you stop eating when you are comfortable.
• Choose satisfying foods. Steer away from foods that give you a lot of calories for very little volume – foods high in fat and sugar such as milk shakes, cookies, and chocolate. The higher the fiber, protein, and/or water content of a food or meal, the more likely it is to be satisfying in your stomach without going overboard on calories. Include whole grains (fiber), fruits and vegetables (fiber + water), and lean meat or beans (protein) for a very satisfying meal.

Journal Reference:
Paul S. MacLean et al. Obesity and Overfeeding Affecting Both Tumor and Systemic Metabolism Activates the Progesterone Receptor to Contribute to Postmenopausal Breast Cancer. Journal of Cancer Research. Published OnlineFirst December 7, 2012; doi: 10.1158/0008-5472.CAN-12-1653

Additional Resources:
The National Cancer Insitute