Energy expenditure: measurement of human metabolism.

Obesity is one of the most prevalent chronic diseases globally, especially in the United States. While the United States gained an early lead in unnecessary weight gain, most other countries are quickly closing the gap. The latest U.S. National Health and Nutrition Examination Survey (NHANES, http://www.cdc.gov/nchs/nhanes.htm) documents that about one third of adults in the United States are now overweight [a body-mass index (BMI) between 25 and 30 kg/m2] and another one third (61 million) are considered obese (BMI >30 kg/m2). Being obese is a strong risk factor for cardiovascular diseases, type 2 diabetes, osteoporosis, some cancers, and depression. The economic impact of this condition is staggering: in 2008, more than 147 billion dollars were spent just in the United States for medical costs related to obesity. Time lost from work and spending on weight loss costs even more.