NEW YORK (Reuters Health) - If the trends of the past three decades continue, it’s possible that every American adult could be overweight 40 years from now, a government-funded study projects.

Pedestrians walk across the street near Times Square in a 2007 photo. REUTERS/Lucas Jackson

The figure might sound alarming, or impossible, but researchers say that even if the actual rate never reaches the 100-percent mark, any upward movement is worrying; two-thirds of the population is already overweight.

“Genetically and physiologically, it should be impossible” for all U.S. 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 told Reuters Health, 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 U.S. adults have extremely high rates of overweight and obesity; among African- American women, for instance, 78 percent 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 percent of American adults will be overweight by 2030, with an obesity rate of 51 percent. By 2048, all U.S. adults could be at least mildly overweight.

Weight problems will be most acute among African-Americans and Mexican- Americans, the study projects. All black women could be overweight by 2034, according to the researchers, as could more than 90 percent of Mexican-American men.

All of this rests on the “big assumption” that the trends of recent decades will march on unabated, Liang acknowledged.

“This is really intended as a wake-up call to show what could happen if nothing changes,” she said.

Waistlines aren’t the only thing poised to balloon in the future, according to Liang and her colleagues. They estimate that the healthcare costs directly related to excess pounds will double each decade, reaching $957 billion in 2030 -- accounting for one of every six healthcare dollars spent in the

U.S.

Those financial projections are based on Census data and published estimates of the current healthcare costs attributed to excess weight -- and they are probably a “huge underestimate” of what the actual costs will be, Liang 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, 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.

“It really needs to be more than an individual effort,” Liang said. “It needs to be a societal effort.”

SOURCE: Obesity, online July 24, 2008.