Obesity’s not something that has one simple “cause.” It’s influenced by a number of factors, from the foods you eat to the type and amount of exercise you do to your family’s genetic makeup. Beyond food, fitness and your genes, here are a few of the major culprits in weight gain and loss: Stress: People who are...

We hear it all the time, especially around the start of each new year: Many Americans are fat. On average, we weigh more—and eat more— than people in most other countries, as well as our parents and grandparents did. Plus, the problem is starting so early that we’re now seeing some of the most severe...