The study suggests that weight gain could not only increase chances for colon and breast cancers as doctors previously suspected, but also for cancer of the esophagus, thyroid, kidney, uterus and gall bladder.

More than 280,000 subjects, both overweight and normal weight, from North America, Europe, Australia and Asia were followed for about nine to 15 years, with researchers tracking their body mass index and correlating it with incidents of cancer.

In men, an average weight gain of 15 kg (33 pounds) increased the risk of esophageal cancer by 52 percent, thyroid cancer by 33 percent, and colon and kidney cancers each by 24 percent. In women, a weight gain of 13kg (29 pounds) increased the risk of cancer in the uterus and gall bladder by nearly 60 percent, esophagus by 51 percent and kidney by 34 percent.

While the study suggests a link, there is no definitive proof that being fat in itself causes cancer. One of the hypotheses is that the presence of excess fat cells could affect the levels of hormones in the body, which may favor the development of tumors in humans.

"To make the link between cause and effect, we need to tick several boxes," said Dr. Andrew Renehan, the study's lead author and senior lecturer at the School of Cancer Studies at the University of Manchester. "This study begins to tick the first two or three boxes, but more research is needed to confirm it."

"The simple message is that, if you manage to keep a healthy body weight, you will have a lower risk of developing cancer," said Ed Yong of Cancer Research United Kingdom.

(Xinhua News Agency February 15, 2008)