Excess fat around the waist increases the risk of bowel cancer even if the rest of the body is slim, experts say.
For every extra inch on the waist above a healthy measurement, the risk of bowel cancer goes up 3pc.
Experts concluded a big waist circumference is a predictor of bowel cancer, regardless of overall body mass index (BMI).
The research, from experts at Imperial College London and the University of Leeds, will be presented at an international cancer conference today.
It focuses on a review of seven existing papers which found tummy fat is a predictor for bowel cancer.
The review provides the strongest evidence so far that the link remains true, even if the rest of the body is in proportion and the person is normal weight or only moderately overweight.
As a guide, a health 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 (90cm) for Asian men.
Prof Martin Wiseman, of the World Cancer Research Fund, said: "Scientists now say that, after not smoking, maintain-ing a healthy weight is the most important thing you can do for cancer prevention."