Obesity, cancer and bacteria in the gut: Scientists explore link

Scientists are learning more about why obese people are at risk for certain types of cancer. Bacteria in the digestive system might have something to do with it.
(Ronaldo Schemidt/AFP/Getty Image)

It’s well known that obesity is linked to diabetes, heart troubles and other health woes, but studies have also linked carrying too much weight to an increased risk of some kinds of cancer, including esophageal, colorectal, pancreatic and other cancers.

Now researchers may have figured out why being overweight is linked to a person’s chances of developing liver cancer: obesity seems to cause key changes in microbes that live in the gut, stimulating bacteria there to secrete chemicals that damage DNA and lead to the development of tumors.

MORE ON MICROBES: Bacteria at the roller derby

Writing Wednesday in the journal Nature, a team of scientists led by Eiji Hara of the Japanese Foundation for Cancer Research in Tokyo described how they induced cancers (click here for report, subscription required for full text) in mice by treating newborn pups with a carcinogen known to produce various types of tumors.


Then they fed half of the mice a normal diet and half a high-fat diet. All of the mice on the high-fat diet developed liver cancer; the mice on the normal diet did not. Separately, the team also gave the carcinogen to mice that were genetically obese who were not fed the high-fat diet. Those animals, too, developed malignancies -- indicating that the obesity, and not the diet itself, was causing the cancers.

The team used a bioluminscent signal to track a chemical in the mice that promotes cellular shutdown as tissues age, finding that mice with the liver cancers had more of the chemical. The senescent cells had something to do with the cancers -- and certain bacteria found in the obese mice, the team found in further experiments, secreted a bile acid known as deoxycholic acid (DCA) that damaged DNA and created the senescent state.

Treating the mice with antibiotics to wipe out the DCA-producing microbes reduced liver cancers.

“It is clear that the increased levels of DCA produced by gut bacteria play key roles in the promotion of obesity-related” liver cancer, the authors wrote.

In an editorial accompanying the study, Harvard researchers Suzanne Devkota and Peter J. Turnbaugh wrote that the Japanese scientists’ work presented “a plausible link” between DCA and liver cancer.

“Microbial bile-acid metabolism may provide an under-appreciated mechanism by which our decisions at the dinner table can translate to disastrous consequences for our health,” they wrote.

The study is just the latest in a wave of work detailing how the microbes that live in each of us affect our health, for better and for worse. To learn more about the microbiome, check out recent stories in the Los Angeles Times on the fungi that live on our feet, the microbes that live on our dogs, and scientists who are studying gut bacteria.

Nature News has this story about the Japanese research.

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