The research team from University of Texas at Austin have identified pathways by which calorie restriction and exercise can modify a postmenopausal woman's risk of breast cancer.
They found that both caloric restriction and exercise affect pathways leading to mTOR, a molecule involved in integrating energy balance with cell growth.
Dysregulation of the mTOR pathway is a contributing factor to various human diseases, including cancers.
Diet and exercise reach mTOR through different means, with calorie restriction affecting more upstream pathways, which could explain why caloric restriction is more efficient in delaying tumour growth than exercise in animal models.
"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 tumour growth," she added.
The research suggests 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.
Increased levels of leptin and decreased levels of adiponectin have been associated with breast cancer risk.
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.
The study showed that blood levels of leptin, a hormone that plays a role in fat metabolism, were significantly reduced in the calorie-restricted mice while blood levels of adiponectin showed an increase.
She also 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.
The study was presented at the American Association for Cancer Research's Seventh Annual International Conference on Frontiers in Cancer Prevention Research.