Obesity is associated with increased risks of certain types of cancers, such as colorectal and liver cancer. The mechanism behind this relationship in humans is still unknown, but recent research has shown that gut microbiota may play a role. Scientists at the Cancer Institute of the Japanese Foundation for Cancer Research in Tokyo studied the relationship between gut microbes and the development of liver cancer using lean and obese mice. By exposing the mice to a cancer-causing chemical shortly after birth, all of the obese mice and a few of the lean mice developed cancer. The cancerous tumors in the obese mice contained a very high level of deoxycholic acid (DCA), which is known to damage DNA and cause inflammation of the liver. DCA is a byproduct of the break down of bile acids by certain gut microbes. The next question was what led to the increased levels of DCA. The scientists found that the obese mice have a different mix of bacteria in their guts, including gram-positive bacterial strains that are less existent in lean mice. They proved that this mix of bacteria was associated with increased DCA levels. An antibiotic targeting the gram-positive bacteria led to decreased DCA levels and reductions in cancer incidence.

Therefore, the mechanism is as follows. Obesity causes gut microbiology changes. Gut bugs that are gram-positive bacteria strains leads to elevated levels of DCA in the body. The more DCA present, the greater the risk for developing liver cancer. If further research proves that a similar mechanism is seen in humans, then this information can be used to screen for liver cancer and to decrease ones risk of developing cancer.