Weight gain can result from an increase in body fluid, muscle mass, or fat. An increase in body fluid can come from medications, fluid and salt retention, intravenous fluid infusion, kidney or heart failure. An increase in muscle mass is commonly seen with exercising. An increase in body fat is commonly seen as a result of diet or lack of exercise as the body converts muscle to fat. An excessive weight gain is referred to as obesity. Obesity is a function of environmental (diet, exercise, lifestyle, etc.), hormonal, and inherited (genetic) factors in varying degrees. Weight gain is a normal part of pregnancy.