The dangers of a pot belly or ‘muffin top’ were highlighted by a large-scale review of studies into Britain’s second biggest cancer killer.
Crucially for the millions battling to contain middle-age spread, it found that you don’t need to be overweight for a generous waistline to cause problems.
Professor Martin Wiseman, medical and scientific adviser for the World Cancer Research Fund, which funded the review, said: ‘This latest study adds to the already strong evidence that carrying excess body fat increases your risk of cancer.
‘In fact, scientists now say that, after not smoking, maintaining a healthy weight is the most important thing you can do for cancer prevention.
‘We estimate that more than 2,700 cases of bowel cancer a year in the UK could be prevented through people maintaining a healthy weight.
‘But this study has also strengthened the evidence that where we carry the fat is important.’
A healthy waist measurement is defined as less than 31.5in (80cm) for women, less than 37in (94cm) for white and black men and less than 35in (89cm) for Asian men.
The differences are down to variations in the average height of ethnic groups, and therefore variations in body mass index measurements.
For every extra inch on the waist above these levels, the risk of bowel cancer goes up 3 per cent, the Imperial College London review of seven pieces of research found.
Dr Teresa Norat, who led the review, told a cancer conference: ‘This indicates that people should pay attention to abdominal fatness even if they are in the normal range of weight, and it confirms that being overweight increases the risk of this type of cancer.
More research is needed to understand how abdominal fatness can be prevented in both normal and overweight individuals.’
It is unclear why abdominal fat is especially dangerous but some scientists believe it may be because it disrupts the balance of hormones that help fuel bowel cancer.
More than 38,000 cases of bowel cancer are diagnosed a year in the UK, and it claims more than 16,000 lives. Only lung cancer kills more.
The World Cancer Research Fund has repeatedly warned that eating processed meats – including bacon, ham, pastrami, salami and hot dogs – significantly raises the chances of bowel cancer.