Significant weight loss may not protect an obese person from cancers of the colon or liver, according to a recent study in obese mice.
The study, “Weight loss following diet-induced obesity does not alter colon tumorigenesis in the AOM mouse model,” published in the American Journal of Gastrointestinal and Liver Physiology, additionally suggests that weight loss after a cancer has begun may impact liver repair mechanisms.
Epidemiological studies and others strongly associate obesity with an increased cancer risk. In a large study in men, for example, colon cancer was nearly twice as likely, and liver cancer 4.5 times more likely, to occur in obese participants compared to those of normal body weight.
For this reason, some suggest that these two cancers might be prevented through lifestyle changes, but to date few studies have looked at the effects of weight loss, following obesity, on the risks for colon and liver cancer.
Researchers at the University of South Carolina investigated whether reducing fat intake in obese mice was enough to protect them from cancer.
The team fed the mice a high-fat diet to mimic human obesity, and then induced weight loss in a subset by switching these mice (called “lean” mice) to a low-fat diet. Next, all the mice were exposed to a carcinogen to assess whether weight loss protected against the development of colon cancer polyps.
Researchers found that lean and obese mice had similar incidence of colon cancer: “[T]here were no significant differences in the polyp number (adenoma), polyp size, or grade of dysplasia,” the researchers wrote, suggesting that weight loss did not protect mice from cancer.
Additionally, the team found that weight loss in obese mice also led to the appearance of cancerous lesions in the liver, accompanied by an increase in the numbers of macrophages and T-cells, suggesting liver inflammation.
“These data suggest that intentional weight loss following chemical-induced carcinogenesis does not affect colon tumorigenesis but may in fact negatively impact liver repair mechanisms,” the researchers wrote.
Further studies, they said, are now required not only to unravel the mechanisms through which obesity induces long-lasting effects on cancer risk, despite weight loss, but also to validate the findings in humans.