According to World Health Organization, in 2010 there were over 1 billion overweight adults worldwide with 400 million adults who were obese. Obesity is a major risk factor for diabetes, cardiovascular disease, musculoskeletal disorders, obstructive sleep apnea, and cancers (prostate, colorectal, endometrial, and breast). Obese people may present to the gastroenterologists with gastroesophageal reflux, non-alcoholic fatty liver, and gallstones. It is important, therefore, to recognize and treat obesity. The main cause of obesity is an imbalance between calories consumed and calories expended, although in a small number of cases, genetics and diseases such as hypothyroidism, Cushing's disease, depression, and use of medications such as antidepressants and anticonvulsants are responsible for fat accumulation in the body. The main treatment for obesity is dieting, augmented by physical exercise and supported by cognitive behavioral therapy. Calorie-restriction strategies are one of the most common dietary plans. Low-calorie diet refers to a diet with a total dietary calorie intake of 800-1500, while very low-calorie diet has less than 800 calories daily. These dietary regimes need to be balanced in macronutrients, vitamins, and minerals. Fifty-five percent of the dietary calories should come from carbohydrates, 10% from proteins, and 30% from fats, of which 10% of total fat consist of saturated fats. After reaching the desired body weight, the amount of dietary calories consumed can be increased gradually to maintain a balance between calories consumed and calories expended. Regular physical exercise enhances the efficiency of diet through increase in the satiating efficiency of a fixed meal, and is useful for maintaining diet-induced weight loss. A meta-analysis by Franz found that by calorie restriction and exercise, weight loss of 5-8.5 kg was observed 6 months after intervention. After 48 months, a mean of 3-6 kg was maintained. In conclusion, there is evidence that obesity is preventable and treatable. Dieting and physical exercise can produce weight loss that can be maintained.