Obesity can be classified into primary and secondary obesity according to its causes. Primary obesity, also known as simple obesity, is the most common type among various forms of obesity. It is mainly caused by poor dietary habits such as overeating, especially excessive intake of fatty foods, and a sedentary lifestyle, rather than being secondary to other diseases. Secondary obesity, on the other hand, is often due to diseases of the hypothalamic-pituitary axis, hypercortisolism, hypofunction of the thyroid or gonads, insulinomas, and other diseases. Secondary obesity is mainly due to diseases, and it can show some symptoms of the underlying disease.