Researchers have revealed in an animal study that although body fat can stimulate the growth of breast cancer cells, this can be counteracted by exercise. The link between obesity and breast cancer has been suspected for years, and it has been a growing concern.

A research team at York University in Canada, led by Professor Michael Connor,  has shown that diet determines the tumor microenvironment by affecting hormonal balance. The study, “Voluntary physical activity abolishes the proliferative tumor growth microenvironment created by adipose tissue in animals fed a high fat diet,” was published in the Journal of Applied Physiology.

Adipose tissue (body fat) stores energy and regulates metabolism and hormone balance. Normally, fat cells produce more than 400 hormones, known as adipokines, which are released into the blood stream. Among the most-produced hormones by adipose tissue are adiponectin (ADIPO) and leptin (LEP). In obese people the balance between these two hormones changes. ADIPO decreases and LEP increases in the circulation, creating a microenvironment that promotes tumor growth.

“Our research has found that the characteristics of hormones produced by fat cells in obese people can promote breast cancer growth, whereas in lean people it prevents growth,” Connor said. “The characteristics of those hormones differ depending on whether the person is lean or obese, and that determines whether the cancer grows or not.”

The team fed rodents a high-fat diet, then removed their adipose tissue to a petri dish, where it promoted the growth of cancer cells. But if animals had free access to a running wheel, the increased physical activity re-established the normal levels of DIPO and LEP. As a result, adipose tissue could no longer promote tumor growth. This data suggests that interventions targeted at obesity may counteract the life-threatening effects of breast cancer.

“Our study shows that voluntary and rigorous exercise can counteract, and even completely prevent, the effects on cancer growth that are caused by obesity. We also show that even moderate exercise can lead to slowing of breast cancer growth and that the more exercise you do, the greater the benefit,” Connor said.

The study suggests ADIPO and LEP hormonal imbalance contributes to a poor response to therapy and a higher risk of death in obese patients.