Food — not lack of exercise — fuels obesity, study findstoggle caption PCH-Vector/iStockphoto via Getty ImagesBack in the 1800s, obesity was almost nonexistent in the United States. If differences in calorie burn can't explain why some countries have higher obesity rates than others, then it must be something else. Mozaffarian was not involved in the study, but he says it adds to other recent research that suggests food is the biggest driver in obesity. "And I think what this study shows is that there's really complicated biology happening and that our food is driving this." Pontzer says if we want to tackle obesity, the public health message should focus on changing what's on our plates.