The findings come as epidemiologists have noted rising rates of liver cancer amid falling rates of cancer generally.
Obesity is a known risk factor for certain cancers—particularly of the gastrointestinal tract. So, people who are obese would reduce their cancer risk by losing weight, right?
Maybe not, a study found.
Research published this week in the American Journal of Gastrointestinal and Liver Physiology finds that losing large amounts of weight may not offer protection against colon and liver cancer, based on experiments with mice.
The study from the University of South Carolina involved 2 groups of mice. Both were fed diets to make them obese, but then 1 group was put on a diet until the mice lost weight and became lean. Then, both groups of mice were exposed to a carcinogen, along with mice from a control group. Both the obese mice and the group of mice that were previously obese developed tumors at the same rate, which was higher than the control group.
“There were no significant differences in the polyp number, polyp size, or grade of dysplasia,” in the obese and lean groups, the team wrote.
Cancer incidence persisted in the newly lean mice, despite other health improvements in this group. “Body weight loss and excess fat reduction did not protect mice from colon cancer progression and liver dysplastic lesion,” the authors said in their abstract, “even though these mice had improved blood glucose and leptin levels.”
Do the results bode poorly for humans who lose large amounts of weight? More study is needed, the authors wrote. “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.”
The study comes as epidemiologists note the rising rates of liver cancer, which have been linked to obesity and alcohol use. Rates of liver cancer are increasing even while rates from other types of cancer have been declining.
A report from March 2016 from the CDC, the National Cancer Institute, and the American Cancer Society found that between 2008 and 2012, liver cancer rose an average of 2.3% per year, and deaths from this cancer rose 2.8% each year among men and 3.4% each year among women.
Velazquez KT, Enos RT, Carson MS, et al. Weight loss following diet-induced obesity does not alter colon tumorigenesis in the AOM mouse model. Am J Physiol, 2016; 311(4):G699. DOI: 10.1152/ajpgi.00207.2016