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Gastric bypass surgery for severe obesity alters bile acid and thus possibly protects against colorectal cancer / Animal model and patient data show important correlation

Every year, more than 60,000 people are diagnosed with bowel cancer, one of the most common types of cancer in Germany. People who are very overweight have an increased risk. A recently published study shows that a surgical gastric bypass not only helps to reduce weight in the long term and prevent secondary diseases. The operation could also reduce the risk of developing bowel cancer. In a study published in the journal Science Translational Medicine on June 25, 2025, researchers from the University Medical Center Freiburg report that gastric bypass significantly reduced the risk of colorectal cancer in mice and almost completely prevented the formation of metastases. Bile acids play a decisive role in this. Initial patient data confirms the connection.

"People with obesity have an altered bile acid metabolism. We were able to show in an animal model that a gastric bypass has an effect on the composition of bile acids and thus reduces the risk of colorectal cancer," says Dr.Rebecca Kesselring, head of the study at the Department of General and Visceral Surgery at the Freiburg University Medical Center. "A gastric bypass could therefore significantly reduce the risk of bowel cancer in people at risk," says Kesselring.

A gastric bypass is a surgical procedure to treat severe obesity and metabolic syndrome. It involves reducing the size of the stomach and bypassing part of the small intestine. This allows food to reach deeper parts of the intestine more quickly - which makes you feel full more quickly and changes the hormone and bile acid balance in the body.

Bile acids as a key factor

Kesselring's research team compared three groups: Mice that had lost weight with gastric bypass, weight-reduced animals without surgery and obese control animals with sham surgery. The results showed that only the bypass protected against tumors. At the same time, the researchers discovered that the composition of the bile acid had changed significantly as a result of the operation. Diverting the bile acid directly into the lower small intestine had the same protective effect.

Confirmations on human tissue and in patients

Laboratory experiments with tumor organoids, human mini-tumors, confirmed the mechanism: certain bile acids accelerated cell division and thus potentially tumor growth, while their absence slowed growth. For clinical classification, the scientists analyzed blood samples from 41 patients with colorectal cancer and later liver metastases. Those with high levels of primary bile acids developed new metastases more than a year earlier on average than those with low levels.

"These results are an important step towards understanding the rising incidence of colorectal cancer, especially in young patients, and protecting people from colorectal cancer in the future," says Prof. Dr. Stefan Fichtner-Feigl, Medical Director of the Department of General and Visceral Surgery at the Freiburg University Medical Center.

In further studies, Rebecca Kesselring's oncoimmunology working group wants to investigate whether the composition of bile acid can be influenced therapeutically without surgery - for example, through special drugs or through combined interventions on the stomach and bile duct. Larger studies are also planned to use bile acids as a biomarker for the risk of metastasis.

Original title of the publication: "Metabolic surgery reduces CRC disease progression through circulating bile acid diversion"
DOI: 10.1126/scitranslmed.ads9705
Link: https://www.science.org/doi/10.1126/scitranslmed.ads9705