It's partly the sedentary lifestyles, but the real problem is the restaurant/fast food, which is very calorie-dense, rich in fat and sugar (high fructose corn syrup, a type of sugar, is extremely cheap because corn is very cheap to grow; corn is used as a filler in many processed products). That stuff is delicious lol, but contrary to popular belief, vegetables are much cheaper than fast food. I'm sure you know about fattening food as an Italian lol, though I hear the food in Italy isn't nearly as fattening as our Italian-style American food, which is all cheese, bread, butter, and pasta of course. The U.S. has an over-eating epidemic. The older generation is eating the same portions of fast food, but over time, the foods have gotten richer, hence they are technically eating more. No one knows how to cook, and many people consider it a waste of time (contrary to Italy and Spain, where I believe cooking and eating together is considered a nice family activity?) so it's common to eat out a lot. The most common home-cooked meals are mostly meat, pasta, or contain tons of cheese. The average obese American has no idea how much they overeat. A close family member of mine is in the highest class of obesity. She has no idea how to cook, makes herself absolutely revolting amalgamations of food in the crock pot once a week and freezes it to eat the rest of the week. Obviously, eating like this is complete suffering, so she always craves delicious fast food, and I think eats more of it than she admits to me.

Your people may get cancer from smoking, but obesity also causes cancer :( Anyways, my main point was that it's not cheaper to eat fast food in the U.S., but a ton of people believe that, especially poor people. But vegetables, fruits, rice, and beans are very cheap; meat and premade foods are very expensive. Cheese is a little expensive. It seems like no one wants to take personal responsibility for becoming obese, and it's true that several industries make a ton of money off of it so they encourage it, but at the end of the day, it is possible to be a healthy weight in the U.S., and it's also cheaper, not only because the food is cheaper, but you will save on healthcare costs. The myth that it's "expensive to be thin in the U.S." only serves to benefit those predatory industries.