Saturday, November 22, 2008

Calorie Restriction And Exercise Show Breast Cancer Prevention Differences In Postmenopausal Women

Calorie Restriction And Exercise Show Breast Cancer Prevention Differences In Postmenopausal Women

Epidemiological data has suggested that inducing a so-called "negative energy balance" (where less energy is taken in than expended) through eating a low-calorie diet or increasing exercise levels, decreases the postmenopausal breast cancer risk associated with obesity. Although the mechanism responsible for these anti-obesity strategies was unknown, scientists have suspected hormone alteration plays a critical role. Increased fat tissue is known to be associated with alterations in adipokines, proteins secreted by fat tissue that help modify appetite and insulin resistance. For example, increased levels of leptin and decreased levels of adiponectin have been associated with breast cancer risk.

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The calorie-restricted mice and the exercised mice showed no significant difference in percentage of body fat, but both groups had significantly less body fat than the sedentary mice that were fed at will.

In addition, blood levels of leptin, a hormone that plays a role in fat metabolism, were significantly reduced in the calorie-restricted and exercised mice compared to the controls. The calorie-restricted mice also displayed increased blood levels of adiponectin, a hormone produced in fat tissue that regulates some metabolic processes, compared to the exercised mice.

Some of the cell signaling pathways regulated by these hormones converge at mTOR, Nogueira explains. She and her colleagues found that the key proteins found downstream of mTOR activation were less active in both the calorie-restricted and exercised mice compared to the controls.

"These data suggest that although exercise can act on similar pathways as caloric restriction, caloric restriction possesses a more global effect on cell signaling and, therefore, may produce a more potent anti-cancer effect," Nogueira said.

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