Obesity: an epidemiological perspective from Asia and its relationship to gastrointestinal and liver cancers.

Obesity is major health problem in the Asia-Pacific region. The proportion of people who are overweight and obese in the region has increased dramatically and is closely linked to the increasing affluence in the region. While the body mass index has been used as a yardstick in many published studies, it has been noted that Asian patients have a greater percentage body fat for a given body mass index and especially abdominal or visceral obesity. The association of obesity and cancers is intriguing and worrisome at the same time, as obesity is rising exponentially throughout the world especially in the Asia-Pacific region. Evidence of its association with gastrointestinal cancers is well documented and is reported with cardioesophageal, colorectal, liver, pancreatic, and gallbladder cancers. The strength of association varies between individual cancers but is of particular concern with colorectal cancer, which is perhaps the fastest emerging cancer in this region. Biological mechanisms for obesity-related carcinogenesis have been described, which includes insulin resistance and secretion of adipokines and chronic inflammation. A "dose-response" relationship between severity of excess body weight and risks of cancer has been reported. However, there is a paucity of data looking at a decrease in incidence of these cancers with a decrease in body weight with treatment, for example, bariatric surgery. Such studies will be difficult to perform and which would require a long period of longitudinal follow-up.