A woman's chances of developing cancer of the breast, endometrium, colon and kidney rise by 10 percent for every 10 years that she is overweight (PLOS Medicine, published online Aug. 16, 2016). Being overweight is also associated with many other cancer-risk factors such as smoking, lack of exercise, poor diet and type 2 diabetes.

People who have cancer and are also overweight are at increased risk for having the cancer spread through their bodies. A new study from the University of Colorado shows how excess weight may spread cancer cells through the body (Cell Stem Cell, July 7, 2016;19(1):23-37). This same mechanism also can explain how being overweight markedly increases a person's risk for many types of cancers.

The researchers found that:
• Mice with leukemia had fatty tissue that had a markedly increased number of stem cells that become cancer cells, compared to other types of tissue in their bodies.
• These cancerous stem cells were growing excessively in fatty tissue because they had a different main source of energy than ordinary cancer cells use. Cancer cells usually use sugar as their main source of energy to help them grow and spread through the body, but the cancerous stem cells in fatty tissue used primarily fat as their main source of energy. In fact, these cancerous stem cells produced chemicals to release fat from fatty tissue so that the stem cells could then use the fat for the energy necessary to help them grow and spread through the body.
• Researchers then gave the mice standard chemotherapy to kill the cancer cells and found that the cancer cells that were in fatty tissue were far more resistant to the chemotherapy than the advanced cancer cells that were outside fatty tissue and used sugar primarily for energy.
• The researchers then showed that the same mechanisms apply to human cancer cells in petri dishes. The authors suggest that further studies may show that human leukemia cancer cells that live in fat and get their energy primarily from fat (instead of sugar) are also far more resistant to chemotherapy than leukemic cells that get their energy primarily from sugar.

How Does Excess Weight Increase Risk for Some Types of Cancers?
Many studies show that cancer can start in stem cells. Normal humans develop millions of new cancer cells every day. However, a healthy person's immunity can tell that cancer cells are different from normal cells and search them out and kill them in exactly the same way that your immunity kills invading germs.

This study suggests (but it remains to be proven) that:
• Having lots of extra fatty tissue in your body means more places for stem cells in fatty tissue to mutate to become cancer cells that can use fat for energy
• Cancer stem cells in fatty tissue that primarily use fat for energy may be more resistant to your immune system's ability to clear cancer cells from your body.

My Recommendations
Avoid being overweight, since excess weight is associated with increased risk for many different types of cancers, diabetes, heart attacks, strokes and premature death. If you already have a cancer and are overweight, try to lose the extra weight. At present, extensive research shows that intermittent fasting may be the most effective method for long-term weight loss.