Today, there is an epidemic in the United States that was not apparent 50 years ago. This epidemic is obesity amongst adults and children in this country. Blame for obesity has been set upon processed foods and sedentary lifestyles, but it wasn’t until Eiji Hara of Tokyo turned his attention towards microbes in the intestine that other significant factors were considered to be risks of obesity as well.

Hara executed two types of experiments. In one experiment, he fed mice different diets to make them obese or lean, but each group was still exposed to a carcinogen. In another experiment, he focused on mice genetically susceptible to being obese even while fed a normal diet.

In his first study, all the obese mice developed cancer while only 5% of the lean mice developed cancer from the exposure to the carcinogen. This study showed that obesity does indeed increase the risk of cancer in obese animals. When Hara studied mice that were genetically susceptible to being obese even while fed a normal diet, he found that they also had a greater incidence of developing cancer.

After Hara had run these two studies, he decided to look at the microbiota in each group of mice and he found that the obese mice had a much higher proportion of gram-positive bacteria rather than gram-negative bacteria. The difference between these bacteria is that gram-positive bacteria has one cell membrane with a thick layer of polysaccharides, called peptidoglycan, on the outside, and gram-negative bacteria have two cell membranes, with a special lipid polysaccharide on the outside dissimilar to peptidoglycan.

Hara also discovered that gram-positive bacteria were more likely to secrete deoxycholic acid, which is an acid formed after these microbes break down bile from the liver. This acid triggers inflammation in the surrounding tissue and DNA damage.  This, in turn, increases the risk of cancer, because damaged cells malfunction and cause tumors.

Though there is more research to be done on this topic, Hara has shown that the possibility of being obese or developing cancer is more than just lifestyle choices. Sometimes, it is out of our control. However, a future plan from this study is to track deoxycholic acid levels in at-risk patients in order to gain a better understanding of how likely they will contract the disease of cancer.