It's one of the world's biggest, and most neglected, public health problems.
According to the World Health Organisation, obesity affects hundreds of millions of people in both industrialised and developing nations. But the wide availability of cheap and fast food in the United States has made the battle against obesity in that country one of the world's most acute.
Now, a new US study predicts American overeating will get even worse, unless radical action is taken to turn things around.
The numbers are staggering. I reviewed dozens of studies to prepare my report on obesity. Most conclude that in the US, roughly one in three Americans is seriously overweight.
Physicians and patients I spoke with told me for decades obese people in the US were told their condition was a result of a lack of will power.
New data on obesity shows that view is changing. Increasingly, obesity is being looked upon by public health officials as a multifaceted affliction and not solely a product of poor decision making by one individual.
Ann is a resident of Baltimore. She asked that I withhold her last name to protect her privacy.
Ann told me how she had struggled for years to manage her weight. She told me when she was obese, basic activities were almost impossible.
"Going up and down stairs, accomplishing simple tasks at home, I couldn't stand up to cook dinner. After 15 minutes I'd have to sit down and rest a couple of minutes," she says.
Ann tried multiple diets with some success, but she says she always gained the weight back. Things changed when she met Dr Larry Cheskin.
Cheskin heads up the Johns Hopkins Weight Management Centre in Baltimore.
He designed an individualised weight loss plan for Ann. After two years, she has lost and kept off an astonishing 110 kilograms. Still, stories like Ann's are rare in the US.
In fact, a just released health research study, from the Robert Wood Johnson Foundation, reports adult obesity is still on the rise, and will afflict more than half of all Americans in 39 states by the year 2030.
Such widespread obesity is expected to increase by 20 times, the number of cases of diabetes, heart disease and stroke in the country.
It's a public health epidemic that Cheskin says is a product of the Western lifestyle of mostly sedentary jobs, high stress and an over-abundance of cheaply produced food.
"Everywhere we turn we're being pushed to eat more and we never need to burn off the calories by exercising,” he told me.
That "food on demand" lifestyle is just part of the reason Americans are gaining weight. It's also part of the reason why each year more than a 100 million Americans try some kind of weight loss programme - a booming business. The diet industry in the US generates annually more than $20bn.
Adding to the problem are the slick advertising campaigns bombarding consumers from diet companies that promise results. The adverts are often endorsed by highly paid celebrities.
Critics say it's an industry that relies on its clients' failure to make its profits.
It's a daunting set of circumstances for millions of Americans. Still, legal activist and law professor John Banzhaf says obesity can be stopped. For 30 years he successfully used lawsuits to take on tobacco companies to improve public health. Now he's taking on some of America's biggest fast food giants for their alleged role in the obesity epidemic.
Banzhaf told me there is a lot that can be done to change the negative food environment he says most Americans fail to overcome.
"We can limit the size of large sugary drinks. We call them liquid candy. You could put a tax based on the number of calories in a product. You can do lots of things and the interesting thing is we know they work, but we lack the political courage to do it," he says. He's using legal action as a tool for change.
Instead of waiting for politicians to solve the obesity epidemic in the US, Banzhaf has launched 10 successful legal actions, against fast food companies like McDonald's and Kraft, among others, related to the problem of obesity.
Banzhaf says the problem of obesity in the US will take years to overcome. He believes it will take many more lawsuits and much more political courage before the number of severely overweight Americans finally begins to come down.