The national cost of obesity, in terms of lost annual productivity alone, would be around $580 billion. Add in the two states whose obesity rate just reaches 50 percent in 2030 -- Virginia and Nevada -- and 41 states will have at least half of the population considered obese. These states are marked here in red. (Brian Fung via DIYMaps.net) 

By 2030, high obesity rates will have spread to the vast majority of the country. At least half of Americans in 39 states will be obese at current rates, according to a joint report out today by the Robert Wood Johnson Foundation and Trust for America's Health. That would bring the national obesity rate to 42 percent, up from 35.7 percent today (according to CDC).

The map above plots what that might look like, with the affected states marked in red, and adds in Virginia and Nevada, the two states projected to have obesity rates of exactly 50 percent. Mississippi is in the most danger: if nothing changes in the next 20 years, just over two-thirds of its population would be obese, contributing to national obesity-related health-care costs of between $147 billion and $210 billion a year, and lost annual productivity to the tune of up to $580 billion.

If we could lower obesity trends by reducing the average adult BMI (body mass index) by only 5 percent in each state, we could spare millions of Americans from serious health problems and save billions of dollars in health spending -- between 6.5 percent and 7.8 percent in costs in almost every state.

Obviously, any long-term projection that presumes the stability of current trends tells us only so much. A lot can change in 20 years, and much is afoot to change it. But one of the necessary preconditions for progress is a good grasp on the magnitude of the challenge before us.