India, July 20 -- Despite exercising regularly and burning more calories than ever, people in wealthier countries are struggling with rising obesity rates. It's a confusing paradox: how can populations that move more and burn more energy continue to gain weight? The answer may not lie in physical activity, but in what's on our plates. (Also read: Man loses 20 kg in 4 months with this simple cardio hack: 'It burns up to 4% more calories per level' )

A March 31 Duke University study challenges the long-held belief that inactivity is the main cause of obesity. By comparing over 4,200 people across 34 populations, from Tanzanian hunter-gatherers to Norwegian office workers, researchers discovered that people in developed nations actually bur...