Soaring obesity rates make the U.S. the fattest country among those involved in a new study conducted by the Organization for Economic Cooperation and Development (OECD).

Since the 1980s, obesity has spread at an alarming rate, the report states. Changes in food supply and eating habits, combined with a dramatic fall in physical activity, have made obesity a global epidemic. Across OECD countries, 1 in 2 adults is currently overweight and 1 in 6 is obese. The rate of overweight people is projected to increase by a further 1% per year for the next 10 years in some countries.

Rates are highest in the U.S. and Mexico and lowest in Japan and Korea, but have been growing virtually everywhere. Children have not been spared, with up to 1 in 3 currently overweight. Severely obese people die 8-10 years sooner than those of normal-weight, similar to smokers, and they are more likely to develop diseases such as diabetes, cardiovascular disease and cancer. Obesity is a burden on health systems, with healthcare expenditure for an obese person at least 25% higher than for someone of normal weight.

Cooperation between governments and the private sector is key to the success of combating obesity, the report says. A prevention strategy combining health promotion campaigns, government regulation and family doctors counseling their obese patients would avoid hundreds of thousands of deaths from chronic diseases every year. It would cost from $10 to $30 per person, depending on the country. Failure would impose heavy burdens on future generations.

The OECD projected that 3 out of 4 people in the U.S. will be overweight or obese within 10 years. Child obesity rates in the U.S. are also highest in the U.S., but growth in obesity has slowed down. Forty percent of American children are currently overweight. Of these, half are obese. Rates have become relatively stable in the last 10 years, suggesting that substantial further growth is unlikely and overweight rates in boys might even begin to fall.