What is the biggest difference between the U.S. and other countries who seem not to struggle with obesity as much?

There is no truly concrete answer for why Americans seem to struggle with obesity more than other nations and cultures. Many experts agree on "The big two" reasons for obesity, which are lack of exercise and overconsumption of calories, especially empty calories (calories with no real nutritional benefit). In the U.S., portion sizes are much larger than other areas of the world, and the quality of the food served in grocery stores and many restaurants is substantially less nutritionally beneficial than in many other nations and cultures around the world. Additionally, the amount of time that younger Americans spend active (walking, running, playing sports, exercising, etc.) is substantially less than the amount of time that adolescents in other countries spend. There are several other possible reasons though, including sleep debt, pollution, unions of obese spouses, and even the presence of air conditioning!