Being obese boosts the risk of half a dozen types of cancer, and the odds strengthen as one's waistline thickens, according to a major review published on Saturday by The Lancet.
Doctors at the University of Manchester, northwestern England, trawled through 141 studies that monitored the health of 282,000 people who gained weight.
Their benchmark of fat was the body mass index (BMI), in which the individual's weight in kilos is divided by the square of the person's height in metres. Individuals with a BMI of 25-29.9 are considered overweight, while those with a BMI of 30 or more are obese.
The investigators found that every gain of five points in BMI among men raised the risk of gullet cancer by 52 percent, of thyroid cancer by 33 percent and of colon and kidney cancers by 24 percent.
Among women, a BMI increase of five points hiked the risk of cancer of the uterus lining by 59 percent, of the gallbladder by 59 percent, of the gullet by 51 percent and of the kidney by nine percent.
Smaller but still significant associations were seen between BMI increase and cancer of the rectum, colon and skin among men, and of the breast, pancreas, thyroid and colon among women. In both sexes, there was an increased risk of leukaemia, non-Hodgkin lymphoma and multiple myeloma.
Obesity has long been linked to deaths from cardiovascular disease and to diabetes in industrialised countries, a phenomenon that is now extending to cities in developing economies.
According to some estimates, deaths from obesity in the United States outstripped those from smoking in 2005.
But only recently has strong evidence emerged of an association between excess body fat and cancer.
A ground-breaking report issued last year by the World Cancer Research Fund and the American Institute for Cancer Research found a link with cancers of the throat, colon, rectum, kidney and, among post-menopausal women, the breast.
In a commentary, also published by The Lancet, Swedish nutritionists Susanna Larsson and Alicja Wolk of the Karolinska Institute in Stockholm speculated that excess body fat may cause changes in levels of insulin, sex steroids and other hormones.
This could have an impact on apoptosis, the mechanism by which a flawed cell commits suicide.
Cancerous cells are able to bypass apoptosis and proliferate unchecked.
Localised accumulation of fat cells could also contribute significantly to specific tumours, such as cancers of the liver and throat, suggested Larsson and Wolk.