It's a problem as old as war.

Troops on the battlefield for weeks or months quickly lose weight because they burn far more calories than they can eat and drink.

From Valley Forge to Afghanistan, American fighters have struggled with the effects of rapid weight loss — a decline of physical strength and mental acuity that could prove fatal in times of war.

“In some cases, they are consuming 50 to 60 percent fewer calories than they are burning out in the field,” said Jennifer Rood, a researcher at Baton Rouge's Pennington Biomedical Research Center who is searching for a solution. “We see a decline in cognition, a decline in attentiveness, vigilance and decreases in mood state."

Rood is recruiting Baton Rouge-area men for a grueling study that in some ways will replicate the troops' experience. While the stresses of war can't be reproduced, Rood's team is slashing the participants' calories while increasing their exercise.

Because under such conditions many soldiers lose testosterone, researchers want to know if giving the servicemembers enough of the hormone to replace their losses can prevent the physical and mental decline caused by rapid weight loss.

"We’re looking at a small subset of the military," Rood said. "This is not for your everyday military person who has a desk job. This is for somebody who is out in extreme stressful conditions in a prolonged period of time with food deprivation and increased calorie expenditure."

Rood is working with the U.S. Department of Defense on the research program called the Optimizing Performance for Soldiers Study. It consists of three parts. First, the participants spend two weeks eating a diet prepared in Pennington's specialized kitchen to become used to the food they will eat in the study. In the second phase, the participants live for 28 days at Pennington where their calorie intake and exercise regimen are monitored every second.

They work out up to three times a day, running on a treadmill, riding a stationary bike or hiking around the research center's campus with a loaded backpack.

"It’s grueling. The first week is pretty grueling," said Danny Tanner, 31, a participant from Gonzales. "The trainers condition you, so it does get better."

In order to understand the precise number of calories they burn, the participants spend a day in a metabolic chamber, which collects the carbon dioxide emitted from the body to quantify that exact calorie count. After that, the program trainers monitor their exercise to ensure they are replicating the calorie expenditures soldiers see in the field.

If a participant burns 2,000 calories a day without exercise, for example, researchers will make sure he burns an extra 1,000 calories through exercise. Then he will consume a little less than 3,000 calories a day.

To test the idea that replacing testosterone could prevent the physical and mental decline, some participants receive a testosterone shot. Throughout the study the researchers test participants' mental and physical conditioning, using MRIs that test brain function.

The third phase of the study focuses on gaining back the 10 to 15 pounds the participants lose.

Researchers are wondering, "What are they gaining when they gain the weight?" Rood said. "Are they gaining back more muscle, or are they gaining back more fat?"

While the focus is on soldiers' performance, the data Rood collects will likely be useful for civilians, too, especially the information about men's metabolism and the effects of testosterone on the body.

It's difficult to find participants who can stay full-time at the research center for nearly a month, but it's an important aspect of the study, said Ryan Lobrano, a 32-year-old participant who has spent three weeks at Pennington.

"They have to make sure we don't sneak a Twinkie or go for a run," Lobrano said while walking around the Pennington lake with a weighted backpack. "Either might throw it off."

Participants are paid up to $6,000 for their time, but it means a leave of absence from their regular jobs and lives. Lobrano, who recently graduated from LSU and left his restaurant job for the study, says the break from work and life was welcomed.

Tanner, who works at an emergency room in Gonzales, was able to take paid time off from work to participate. He is now back at work and trying to gain back some weight.

"I’ve never been in the military, and I’ve always wanted to do something with the military," Tanner said. "Just my civic duty, I guess."

Researchers at Pennington Biomedical Research Center are still seeking men between the ages of 18 and 39 to participate in the Optimizing Performance for Soldiers Study. To learn more, visit pbrc.edu/OPS or call (225) 763-3000.

©2016 The Advocate, Baton Rouge, La.Visit The Advocate, Baton Rouge, La. at www.theadvocate.comDistributed by Tribune Content Agency, LLC.