Morbidly obese patients who surgically reduce their stomach size lower their risk of developing cancer by about 80 per cent, a new study by Montreal researchers suggests.

Researchers from McGill University in Montreal compared 1,035 patients who had bariatric surgery between 1986 and 2002 to 5,746 obese patients who did not have surgery, matching them by age, gender and the length of time they'd had their diagnosis of morbid obesity.

During the five-year followup period, two per cent of patients who had undergone bariatric surgery were diagnosed with cancer, while 8.5 per cent in the non-surgery group were diagnosed with the disease.

In the study presented Tuesday at this week's annual meeting of the American Society for Metabolic and Bariatric Surgery in Washington, D.C., researchers found the risk of developing breast cancer dropped by 85 per cent, and by 70 per cent for colon and pancreatic cancers.

"The relationship between obesity and many forms of cancer is well established," said Dr. Nicolas Christou, director of Bariatric Surgery at the McGill University Health Centre, in a release.

"This is one of the first studies to suggest that bariatric surgery might prevent the risk of cancer for a significant percentage of morbidly obese people."

The patients who had bariatric surgery lost on average more than 67 per cent of their extra body weight. 

Bariatric surgery includes:

  • Gastric bypass surgery, in which a surgeon reduces the capacity of the stomach.
  • Laparoscopic banding, in which the upper part of the stomach is turned into a small pouch that can handle much smaller quantities of food.

Excess body fat has been shown in previous studies to increase hormone production, a major rsk factor in developing hormone-driven cancers like breast and colon. Altering hormonal levels drastically through surgery might lower the risk of developing these cancers, the researchers believe.

According to the 2007 Canadian Community Health Survey, four million people aged 18 or older, or 16 per cent of those surveyed, reported height and weight measurements that put them in the obese category.

Another eight million, or 32 per cent, were overweight.

With files from the Canadian Press