This may be the single most important thing making Americans sick

Americans are great at a lot of things, but it turns out we don't stack up so well against similar countries in terms of our health.

There are a handful of factors that go into putting Americans near the bottom of the bunch, particularly early in life: surprisingly high infant mortality rates, sexually transmitted infections, and problems with drugs and violence - to name just a few.

But one important factor is the amount of extra weight we carry around. Obesity is what's driving a large chunk of the difference between American lifespans and those in other countries; between 42 and 67% of the years lost after age 50 in the US as compared to other countries can be attributed to Americans' extra weight.

Americans consume more than 3,500 calories per day each, among the highest rates worldwide, and those calories have to go somewhere.

Part of the reason obesity is problematic is that it can lead to or increase the risk of a range of health issues: diabetes, injuries, heart disease, some types of cancer, and depression.

And while in some segments of the population, the proportion of people who are overweight may have peaked, obesity rates still aren't really declining, according to Eileen Crimmins, who studies aging and longevity at the University of Southern California.

Moreover, obesity is affecting people earlier in life, when they're traditionally healthiest. "People just gain too much weight too early," Crimmins said. "It's not so clear that it's really killing people, but it is disabling."

Earlier can mean a lot earlier. "Certainly children are also heavier," Crimmins said. That's particularly concerning since childhood is when we develop many of our habits, and as the World Health Organization notes, "childhood obesity is associated with a higher chance of premature death and disability in adulthood."