Gastric bypass surgery may cut the risk of bowel cancer
Weight-loss surgery seems to lower the risk of colorectal cancer by changing where bile acids enter the small intestine, raising the possibility of developing treatments that mimic these effects
By Carissa Wong
25 June 2025
Gastric bypass surgery is generally used for weight loss, but it may have other benefits
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A common form of weight-loss surgery may cut the risk of colorectal cancer by altering levels of molecules called bile acids in the blood and small intestine. The findings could lead to new treatments for bowel cancer.
Gastric bypass surgery involves stapling the stomach to form a small upper pouch and a larger lower pouch. The small intestine is then connected to the upper pouch so food and digestive juices bypass most of the stomach and the start of the small intestine. After having the surgery, people typically feel full sooner and lose weight.
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Prior studies have also linked the procedure to a reduced risk of colorectal cancer, but it was unclear why. To find out, Rebecca Kesselring at the University of Freiburg in Germany and her colleagues fed mice a high-fat diet until they gained around 50 per cent of their initial body weight, on average. They then gave a third of the mice gastric bypass surgery while the rest underwent sham surgery that didn’t rearrange their digestive organs.
Aiming to isolate the effect of having gastric bypass surgery from that of losing weight, the team put the gastric bypass group and half of the remaining mice on a diet that caused them to lose about a fifth of their weight, on average, over six weeks.
The researchers then implanted colorectal cancer cells into the mice’s colons. After another six weeks, they found that colon tumours in the gastric bypass group were two-thirds smaller than those of either the mice that had kept gaining weight or the mice that had lost weight through diet alone.
