HealthDay News — U.S. obesity rates are projected to increase 33%, and severe obesity rates, 130%, during the next two decades, researchers estimate.

“If these forecasts prove accurate, this will further hinder efforts for health care cost containment,” Eric A. Finkelstein, PhD, from the Duke-NUS Medical School in Singapore, and colleagues reported online in the American Journal of Preventive Medicine. Publication coincides with the 2012 Weight of the Nation conference, May 7-9 in Washington, D.C.

The researchers analyzed data from a sample of 3,475,103 nonpregnant adults aged 18 years and older collected from Behavioral Risk Factor Surveillance System (BRFSS) between 1990 and 2008, to estimate the prevalence of adult obesity and severe obesity through 2030.

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Using nonlinear regression models, obesity prevalence is estimated to reach 42% by 2030 —  a rate lower than previous linear time trend forecasts, which put this figure at 51%. The researcher attribute the lower rates “to the assumption that future trends in obesity will follow a logarithmic, as opposed to a linear, trajectory,” which suggests “a leveling-off of obesity for some subpopulations.”

On the other hand forecasts for severe obesity are higher — at 11% vs. 9% forecasted in earlier studies using linear modeling. “These projections were based on data showing higher historical growth for the severely obese subsample,” the researchers explained.

The expected increase in severe obesity rates is particularly concerning, because those with BMIs greater than 40 are at a much greater risk for diabetes and other medical conditions have a shorter life expectancy and higher lifetime medical costs than those with BMIs between 30 and 35, they wrote. This trend suggests that even if overall obesity prevalence levels off, as the model suggests, future healthcare costs may continue to rise.

Rising prices of healthier relative to less-healthy foods and greater Internet access during the study period were individual variables associated with higher odds of being obese (P<0.05 for both), data indicated. The researchers found no association between state-level individual variables and the probability of being severely obese.

“Potential savings in medical expenditures from bending the obesity-prevalence trajectory could be large,” the researchers wrote.

Reducing projected trends in obesity rates just one percentage point would result in 2.6 million fewer obese adults in 2020 and 2.9 million fewer obese adults in 2030. This would translate into $4 billion reduction in obesity-related medical expenditures in 2020 and a $4.7 billion reduction in 2030 (based on 2008 dollars). Furthermore, if obesity were to remain at 2010 levels, the combined savings in medical expenditure over the next 20 years would be $549.5 billion.

The researchers acknowledged several study limitations including the assumption that logistic regression parameters and costs based on past data will remain relevant in the future, reliance on self-reported height and weight and a study population that consisted only of households with land-line telephones.

Childhood obesity trends, which were not measured in this study, could also have a major impact on future adult obesity prevalence and related health-care costs, the researchers noted.

Other unknown variables, including increased access to recreational facilities, improvements in urban design, anti-obesity social marketing programs, work-site health promotion programs and new drugs and technologies also have the potential to slow obesity growth.

“Successful interventions that generate even small improvements in obesity prevalence (…) could result in substantial savings,” the researchers wrote.

Finklestein EA et al. Am J Prev Med. 2012; doi: 10.1016/j.amepre.2011.10.026.