(Reuters Health) - A study of soldiers trying to get into an elite army unit adds to evidence linking healthy diets to better physical performance.

Researchers analyzed data from active-duty male soldiers attending the assessment and selection course for Army special forces, known as Green Berets. They found that soldiers with higher Healthy Eating Index (HEI) scores had higher physical performance scores and were up to 75% more likely than those with the lowest diet-quality scores to be chosen for the elite unit.

To join the U.S. Army Special Forces, soldier must complete a 19-20 day course known for its strenuous physical demands, with more than half of participants dropping out before the end, according to the research team, led by Emily Farina at the U.S. Army Research Institute of Environmental Medicine, Natick, Massachusetts.

Candidates often cite insufficient physical fitness as the reason for their withdrawal, the study team notes.

During the course, the candidates get military rations, which standardizes their diet. As a result, the authors point out, the differences in what soldiers normally ate before the course may have an impact on their physical performance during the testing.

The study used food frequency questionnaires to assess the usual diets of 782 soldiers attending the course in 2015-2017. The HEI score is calculated based on how closely the diet adheres to the U.S. 2015-2020 Dietary Guidelines for Americans, with points for consumption of healthy foods such as whole fruits, total vegetables, protein foods, and deductions for high levels of sodium or saturated fat, for example.

HEI scores range from zero to 100, with higher scores representing a healthier diet.

Soldiers with high scores in physical fitness tests, such as sit-ups and running, had significantly higher HEI scores, on average, than worse-performing candidates, the authors report in Medicine & Science in Sports & Exercise.

Soldiers with the highest dietary scores tended to be over age 25, nonsmokers, with some college education or a bachelor’s degree, and were likely to do more than 400 minutes a week of resistance training like free weights or Olympic lifting.

There were no significant diet-quality differences among soldiers based on time spent doing aerobic or high-intensity training, their stamina, smokeless tobacco use, total calorie intake, officer or enlisted status, or other factors.

The study wasn’t designed to prove that diet quality was responsible for physical performance or soldiers’ odds of passing the course. It’s possible that diet quality reflects a healthier overall lifestyle or greater fitness.

Still, the study authors note that the findings could be used to provide guidelines to soldiers preparing for the course as well as athletes preparing for events to enhance their performance.

The findings showcase the importance of diet and nutrition on physical performance, said Sanford Nidich, director of the Center for Social and Emotional Health at Maharishi University of Management Research Institute in Fairfield, Iowa.

Nidich, who was not involved in the study, said in an email there is also growing awareness that dietary intake is important for mental health and overall behavior.

The study authors did not respond to a request for comment.

SOURCE: bit.ly/2lsDapF Medicine & Science in Sports & Exercise, online September 16, 2019.