Obesity increases risk of developing cancer. And now, a mice study has confirmed that obesity does indeed act as a “bona fide tumour promoter.” Published in the January 22nd issue of the journal Cell, a Cell Press publication, scientists also have good evidence to explain how that happens.

“Doctors always worry about our weight, but the focus is often on cardiovascular disease and type 2 diabetes, both of which can be managed pretty well with existing drugs,” said Michael Karin of the University of California, San Diego. “However, we should also worry about elevated cancer risk. If we can reduce cancer deaths by as many as 90,000 per year, that’s a lot of people - a lot of lives.”

In the study, Karin’s team showed that liver cancer is fostered by the chronic inflammatory state that goes with obesity, and two well known inflammatory factors in particular. To reach the conclusion, Karin’s team investigated mice prone to develop hepatocellular carcinoma (HCC). The mice are typically given HCC either by exposure to a chemical carcinogen, known as DEN, when they are two weeks old, or by exposure to that same carcinogen at three months of age followed by the tumor-promoting chemical phenobarbitol.

In the new study, the researchers gave two-week-old mice DEN and then divided them into two groups - one fed a normal, relatively low-fat food and the other fed on high-fat chow. “It was clear that the mice on the high fat diet developed more liver cancer,” Karin said.

To further confirm the link, they gave DEN to two-week-old mice that were fed a normal diet but carried a gene that made them obesity-prone. Those mice, too, developed more liver cancers, evidence that it wasn’t the high-fat diet that led to cancer, but rather something about the animal’s obese state.

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