Obesity is a cancer risk that rivals smoking as a preventable leading risk factor for cancer death. While cancer is assisted by the hyper-nutrition, gut microbe disturbance, cholesterol, and diabetes that accompany obesity, it is particularly aided by the fifth consequence of being overweight: chronic inflammation.
Chronic inflammation increases cancer risk both in the initiation of the disease, and the progression of the disease, by cultivating an environment that encourages the mutations in cells that lead to cancer. The changes inflammation brings to tissues make them better places for malignant cells to live and grow.
Fat is not just an energy storage tissue. It is also where many inflammatory immune cells live. The more fat we have, the more immune cells there are, pouring out inflammatory molecules that change tissues and increase cancer risk.
A recent study in the journal Science shows that some cancers are actually addicted to obesity, requiring the hyper-nutrition and inflammatory molecules to survive. Breast cancer is promoted by blood vessel growth factors produced by fat cells. Pancreatic cancer is associated with interleukin-1-beta, a immune system suppressor molecule produced by fat cells. Fat cells secrete molecules that allow prostate cancer cells to invade surrounding tissue.
Fat cells also produce estrogen, which can make estrogen sensitive cancers grow faster. They also produces insulin and other growth factors that affect all tissues.
Screening for breast cancer is hindered by surrounding fatty tissue, but worse than that, fat cells produce growth factors that promote metastasis (the spreading of cancer to other tissues such as the lungs). High cholesterol levels associated with obesity also cause breast cancer cells to metastasize. Metastasis is what causes most breast cancer deaths.
Losing weight can help to prevent cancer, and can help prevent existing cancer from spreading. Fasting reduces immune suppression, helping the immune system fight off cancer. Exercise activates natural killer cells in the immune system that seek out and destroy cancer cells.