Weight loss after obesity doesn’t cut risk of certain types of cancer

The researchers studied obese mice ("obese") and obese mice that lost weight ("lean") compared with a control group. All of the mice were fed a high-fat diet. The obese and lean groups were exposed to a carcinogen and studied to observe whether losing weight provided protection against the development of colon polyps or cancer.

The unexpected results: losing weight did not protect the lean group's colon health. "There were no significant differences in the polyp number (adenoma), polyp size, or grade of dysplasia" in the obese and lean groups, wrote the research team.

In addition, scientists found an increase in the markers for the growth of cancerous cells and liver inflammation in both groups exposed to the carcinogen. Larger numbers of T cells were activated in the lean group too, which may relate to repairing damage from the inflammation in the liver. These findings suggest that "excess fat reduction did not protect mice from colon cancer progression and liver dysplastic lesion…even though these mice had improved blood glucose and leptin," according to the researchers.

Further study is needed in this area, according to the research team, but the results may have implications for humans as well. "Our results suggest that intentional body weight loss by diet manipulation does not provide any beneficial effects on colon tumorigenesis and it may in fact aggravate liver capacity of repair."