At a time when American military forces are stretched thin overseas, a growing number of potential recruits are too fat to enlist, according to an analysis by Cornell economists.

In the past half-century, the number of women of military age who exceed the U.S. Army's enlistment standards for weight-for-height and body fat percentage has more than tripled. For military-age men, the figure has more than doubled. As of 2007-08, 5.7 million men, or nearly 12 percent, and 16.5 million women, about 35 percent, of military age are ineligible for duty because they are overweight or obese, estimate John Cawley, associate professor of policy analysis and management, and economics doctoral student Catherine Maclean.

The findings, published in September by the National Bureau of Economic Research in a working paper titled "Unfit for Service: The Implications of Rising Obesity for U.S. Military Recruitment," are cause for alarm for the military branches (Army, Navy, Air Force, Marine Corps), which together must attract some 184,000 new service members each year. Fewer able-bodied recruits could also lead the Pentagon to limit its use of troops and rely instead on unmanned aircraft and private security companies to carry out missions, the paper notes.

"Almost one in four applicants to the military are rejected for being overweight or obese -- it's the most common reason for medical disqualification," Cawley said. "With an active war in Afghanistan and continuing operations in Iraq, it is well-known that the military is struggling to recruit and retain soldiers. Having a smaller pool of men and women who are fit enough to serve adds to the strain and creates even more problems for national defense."

Cawley and Maclean also found stark disparities in fitness levels of potential recruits based on race, income and college education. Compared with white females, black and Hispanic females are less likely to meet the weight standards, for instance, making it difficult for the military to achieve its diversity goals.

The study follows a similar report last spring by retired generals and admirals, which noted that more than one-fourth of young adults are medically ineligible for service. But Cawley and Maclean chart the climbing obesity rates over a much longer period, using data from the National Health and Nutrition Examination Surveys spanning 1959-2008. Moreover, the Cornell study estimates the number of civilians who meet the body fat requirements of each military branch, which had not been tracked previously. "We also accessed weight and height records measured by medical professionals, which are more accurate than self-reported data," said Maclean.

Military brass have limited options to fix the problem, Cawley said. They could relax the height-for-weight and body fat standards, but Cawley warned of additional costs to treat obesity-related conditions and associated absenteeism. "Military spending on obesity is over $1 billion annually already," Cawley said. "It's more than the military spends on treating tobacco- and alcohol-related illness combined."

One solution could be to institute more lenient weight standards for noncombat troops. "A computer programmer or cook may not need to have the same level of physical fitness as an infantryman," Cawley said.

Ultimately, Cawley said, the steep decline in military-eligible men and women illustrates the hidden costs of obesity.

"It's another example of the underappreciated public consequences of obesity," Cawley said. "We tend to think of obesity as a personal, individual health problem. But the fact that U.S. military leaders view it as a threat to national security and military readiness shows its far-reaching impact."

Ted Boscia is assistant director for communications in the College of Human Ecology.