As we all know, obesity increases the risk of cardiovascular disease and diabetes, but to say that obesity increases the risk of cancer, surely some people will be skeptical. In fact, there have been more and more studies show that obesity can increase the risk of a variety of tumors, have overtaken smoking, the trend of becoming the first cause of cancer. It is found that the increase of body mass index (BMI) is significantly related to the risk of esophageal adenocarcinoma, thyroid cancer, colon cancer and kidney cancer in men, and endometrial cancer, gallbladder cancer, esophageal adenocarcinoma and kidney cancer in women. In addition, increased BMI was weakly associated with the risk of rectal cancer and malignant melanoma in men, postmenopausal breast, pancreatic, thyroid and colon cancer in women, and leukemia, multiple myeloma and non-Hodgkin’s lymphoma in men and women. In terms of different ethnic groups, the results of the studies in North America, Europe, Australia and Asia-Pacific were basically the same, while the correlation between increased BMI and breast cancer was stronger in the Asia-Pacific population. As for how obesity increases tumor risk, the exact mechanism is not yet known. Researchers believe that changes in hormone levels disrupt the balance between cell proliferation and apoptosis, which is the most likely carcinogenic mechanism. The role of obesity in the development of different tumors may vary, such as changes in adipokine metabolism, local inflammation, hypertension and lipid peroxidation increase the risk of renal cancer, the development of non-alcoholic fatty liver disease increases the risk of hepatocellular carcinoma, abdominal obesity caused by gastroesophageal reflux increases the risk of adenocarcinoma of the esophagus and so on. Experts call: in order to be more healthy, should control weight, avoid obesity.