Thirteen months later, 19.3% of the force had reached that threshold, a rise that continued an upward trend in overweightness and obesity that began decades ago, according to a new study in the Armed Forces Health Surveillance Division's March Medical Surveillance Monthly Report, published Sunday.

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While the assessments did not show an immediate, abrupt jump at the start of the pandemic -- a situation the researchers said may have resulted in higher overall increases across the research period -- the rise is worrisome, given the long-term health consequences of excess weight.

"Not only does obesity within the military ranks negatively impact the professional perception of the military, it also compromises its readiness and leads to functional limitations," wrote the researchers, referring to musculoskeletal injuries, mental health diagnoses, substance abuse, diabetes and other illnesses associated with excess weight that could affect a person's job and performance.

For the study, the researchers reviewed the periodic health assessments of more than 2 million service members from January 2018 through July 2021. They found an overall increase in obesity, along with an abrupt decrease in vigorous exercise in the first year of the pandemic.

Among the services, the Navy had the largest increase in the prevalence of obesity from before the pandemic to afterward, with the Marine Corps a close second. The Army placed third, while the Air Force had the smallest increase.

Those who reported reaching the obesity threshold were more likely to be male, aged 40 or older, Black, junior enlisted, and reported their marital status as "other," meaning they were not married or single persons who had never been married.

They also tended to have some college education and largely were stationed in the South or Midwest. Occupational specialties that saw the largest increases included motor transport and health care, while personnel in combat-specific roles and engineering or repair had the least gain.

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Also according to the study, warrant and junior officers saw decreases in the number of obese service members in their ranks.

During the same time frame, Navy sailors had the largest drop in "vigorous exercise," defined as 150 or more minutes of intense exercise per week, during the study months, while the Air Force had the second biggest drop, followed by the Marine Corps and the Army.

Junior enlisted personnel, along with motor transport and engineering/repair specialties, also reported the large drops in exercise across the study period.

Preliminary results of a separate study on obesity among active-duty personnel during the pandemic that used different research methods found a 27% increase in obesity among soldiers and a 49% increase among Marines.

That research, which has not yet been published, used calculations of height and weight gleaned from the Military Health System Data Repository. It showed that roughly 10,000 soldiers went from having a healthy weight to being overweight, while another 10,000 moved from the overweight category to obesity.

The study showed that 4,500 Marines measured as obese before the pandemic, while 6,400 counted as obese the year after.

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The number of female Marines who became obese during the pandemic more than doubled, from 100 to 220, according to Tracey Perez Koehlmoos, director of the Center for Health Services Research at the Uniformed Services University of the Health Sciences in Bethesda, Maryland, and one of the researchers who ran the study.

Koehlmoos cautioned that the results were preliminary and had yet to be reviewed for publication, but said the findings "pose a challenge" to the services as they seek to retain troops and maintain a healthy fighting force.

"Obesity itself is a huge risk factor with very harmful consequences for chronic disease -- diabetes, cardiovascular disease, cancers, musculoskeletal injuries. Obesity is a condition that puts people's health at risk in general, not just specifically to the military. This is for everyone across the planet," Koehlmoos said during a presentation of the study’s preliminary results April 26 before the U.K.-based C3 Collaborating for Health organization.

Both Koehlmoos and the authors of the Armed Forces Health Surveillance Division study said their research has limitations, including the military's use of the body mass index to calculate fitness and reliance on the tape test, neither of which can tell the difference between muscle mass and fat.

Both the Army and the Marine Corps are studying ways to better measure body fat, using sophisticated scanning tools that could replace the inexpensive tape measurements. But Koehlmoos expressed concern that the research, which is meant to set new baselines and increase understanding of muscle mass, fat and fitness, was conducted on service members during the pandemic, which may result in a "risk of setting standards that aren't based on the regular population."

With roughly 71% of the U.S. adult population unable to serve in the military because they do not meet the requirements -- a result of being overweight or having physical limitations, a criminal history or past drug use -- "reducing attrition and retaining personnel is a constant problem," the AFHSD researchers wrote.

They recommended that the services "identify ways to improve consistent behaviors throughout the year," such as exercising regularly and choosing healthy foods to stem the rising wave of obesity.

"If this increasing obesity trend continues, current anti-obe­sity initiatives including utilization of well­ness centers, dietary options in base dining facilities, and hours restricting access to exercise facilities should be re-examined to better tackle this problem," they wrote.