In the 20 years obesity among adults has risen significantly. Data show that one third of U.S. adults 20 years of age and older have obesity. Obesity continues to be a common, serious and costly disease. Scientists discuss the many different theories explaining why obesity continues to increase despite best efforts at controlling weight gain in this environment, including increased availability and marketing of high-calorie and high-glycemic-index foods and drinks, larger food portions, leisure time physical activities being replaced with sedentary activities such as watching television and use of electronic devices, inadequate sleep, and the use of medications that increase weight.