Having a bulky waist actually causes bowel cancer, and is not just a sign of an unhealthy lifestyle, according to a study that suggests surgical removal of ‘deep fat’ could lessen the risk.
It has long been known that being obese is linked to a high risk of the disease, which kills 16,000 a year in Britain.
But researchers say they have proved that having too much fat - or rather too deep abdominal fat around the organs - causes the disease.
The findings suggest that those who are an ‘apple’ shape will have a higher risk of bowel cancer than those who are shaped like a ‘pear’. The former are already known to suffer higher rates of heart disease.
They also suggest that, particularly in females, surgically removing deep fat could lower the risk of developing intestinal tumours. However, it is unlikely patients would ever be offered such operations for that reason alone.
Dr Derek Huffman, of the Albert Einstein College of Medicine in New York, said: “There has been some scepticism as to whether obesity per se is a bona fide cancer risk factor, rather than the habits that fuel it, including a poor diet and a sedentary lifestyle.
“Although those other lifestyle choices play a role, this study unequivocally demonstrates that visceral adiposity is causally linked to intestinal cancer."
He and his colleagues reached their conclusions after a series of experiments in mice that they knew were prone to developing intestinal tumours. The study is published in the journal Cancer Prevention Research.
They split the mice into three groups to test the relative roles of obesity in general, abdominal fat in particular, and diet and exercise.
Those in the first group underwent “sham” surgery and were then allowed to eat whatever they liked from a mouse “buffet”.
Those in the second had their deep abdominal fat removed, before likewise being put on an unrestricted diet.
Those in the third underwent sham surgery, but were restricted to 60 per cent of the calorie intake of the others, so their deep fat was limited.
Dr Huffman said the mice which were allowed to eat at will and did not have their “visceral fat” removed “developed the greatest number of intestinal tumors, and had the worst overall survival”.
He continued: “However, mice that had less visceral fat, either by surgical removal or a calorie-restricted diet, had a reduction in the number of intestinal tumors.
Dr Andrew Renehan from Manchester University, who advises the charity Beating Bowel Cancer, said research was needed in humans to establish if deep fat caused bowel cancer in people too.
He said: “This type of fat is a strong predictor for diabetes, but we still don’t know its connection with cancer.
"This research provides evidence to support the hypothesis that there is a link, but there is no definitive research to show this in humans. More research is needed to determine the impact of this fat on bowel cancer.”