“One of the few breast cancer modifiable risk factors is obesity,” said lead author Leticia M. Nogueira, Ph.D., a research graduate assistant at the University of Texas. “Our study may provide a good scientific basis for medical recommendations. If you’re obese, and at high risk for breast cancer, diet and exercise could help prevent tumor growth.”
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.
For the study, Nogueira and colleagues sought to compare the changes in adipokines, and their downstream signaling pathways proven to be altered in human breast cancers, following either caloric restriction or exercise in a mouse model of post-menopausal obesity.
For eight weeks, they administered a high-fat diet to 45 mice that had their ovaries surgically removed to model the post-menopausal state. During week nine of the study, the diet-induced obese mice were randomly assigned to one of three groups: a control group, permitted to eat at will; a group fed a diet reduced in calories by 30 percent; and a group that was permitted to eat at will but exercised on a treadmill for 45 minutes a day, five days a week. At week 16, researchers collected tissue from the mice for analysis.
At the study’s end, the mice fed a calorie-restricted diet weighed an average of 19.9 grams – significantly less than the control mice (average weight 28.8 grams) and the exercised mice (average weight 26 grams). 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.
About Breast Cancer
Breast cancer is a malignant (cancerous) tumor that starts from cells of the breast. Breast cancer occurs mostly in women, but men can get breast cancer too. In the U.S., it affects one in eight women. There are many types of breast cancer, though some of them are very rare. Sometimes a breast tumor can be a combination of these types of breast cancer and to have a mixture of invasive and in situ breast cancer cancer. The most common types of breast cancer are: Ductal carcinoma in situ (DCIS) and lobular carcinoma in situ (LCIS). DCIS is the most common non-invasive breast cancer accounting for 85 - 90% of all breast cancer cases.
DCIS means that the breast cancer is only in the ducts. It has not spread through the walls of the ducts into the tissue of the breast. Nearly all women with breast cancer at this stage can be cured. Often the best way to find DCIS early is with a mammogram. LCIS occurs in approximately 8% of all cases, begins in the milk-making glands but does not go through the wall of the lobules. Although not a true cancer, having LCIS increases a woman's risk of getting breast cancer later. For this reason, it's important that women with LCIS to follow breast cancer screening guidelines. Other less common forms of breast cancer include Inflammatory breast cancer (IBC) an invasive breast cancer which accounts for about 1% to 3% of all breast cancers, and Paget's disease of the nipple (a rare type of breast cancer, which can occur in women and men). It shows up in and around the nipple, and usually signals the presence of breast cancer beneath the skin.
Common breast cancer symptoms may include: a lump or a thickening in the breast or in the armpit, nipple discharge, a change of size or shape of the mature breast, fluid (not milk) leaking from the nipple, a change of size or shape of the nipple, a change of color or texture of the nipple or the areola, or of the skin of the breast itself (dimples, puckers, rash). Anyone experiencing breast cancer symptoms should consult a medical professional as soon as possible.