If the trends of the past three decades continue, it's possible that every American adult could be overweight 40 years from now, a leading researcher on a US government-funded study has warned.
The figure might sound alarming, or impossible, but researchers say that even if the actual rate never reaches the 100 per cent mark, any upward movement is worrying; two-thirds of the population is already overweight.
"Genetically and physiologically, it should be impossible" for all US adults to become overweight, said Dr Lan Liang of the federal government's Agency for Healthcare Research and Quality, one of the researchers on the study.
However, she said the data suggest that if the trends of the past 30 years persist, "that is the direction we're going."
Already, she and her colleagues point out, some groups of US adults have extremely high rates of overweight and obesity; among African- American women, for instance, 78 per cent are currently overweight or obese.
The new projections, published in the journal Obesity, are based on government survey data collected between the 1970s and 2004. If the trends of those years continue, the researchers estimate that 86 per cent of American adults will be overweight by 2030, with an obesity rate of 51 per cent.
By 2048, all US adults could be at least mildly overweight.
Weight problems will be most acute among African-Americans and Mexican-Americans, the study projects. All African-American women could be overweight by 2034, according to the researchers, as could more than 90 per cent of Mexican-American men.
All of this rests on the "big assumption" that the trends of recent decades will march on unabated, Dr Liang acknowledged.
"This is really intended as a wake-up call to show what could happen if nothing changes," she said.
The findings highlight a need for widespread efforts to improve Americans' lifestyles and keep their weight in check, according to the researchers. Simply telling people to eat less and exercise more is not enough, Dr Liang noted.
Broader social changes are needed as well, she said - such as making communities more pedestrian-friendly so that people can walk regularly, or getting the food industry to offer healthier, calorie-conscious choices.