Obesity has risen steadily in the United States over the past 150 years, with a marked uptick in recent decades. In the United States today more than 35% of adults and nearly 17% of children aged 2–19 years are obese. Obesity plagues people not just in the United States but worldwide, including, increasingly, developing countries. Even animals—pets, laboratory animals, and urban rats—have experienced increases in average body weight over the past several decades, trends not necessarily explained by diet and exercise. In the words of Robert H.