Fitness types used to love creatine, then they flirted with l-arginine, and now, l-glutamine is the newest crush on the (protein-building) block.

Bodybuilders and high-performance athletes have been using l-glutamine (also referred to as glutamine) supplements and powders for years because of a perception that the amino acid helps you retain muscle and recover from workout strain. Now, the trend has trickled down to more recreational exercisers hitting the gym or boutique fitness studios.

At Barry’s Bootcamp, the workout’s devotees now ask for l-glutamine by name in their smoothies and swear by its magical powers for sore muscles, says Chris Schrier, the manager and walking encyclopedia of nutritional facts at Barry’s Fuel Bar. And trainers all over town have been recommending it after sweat sessions.

WHY ARE FITNESS-GOERS FANS OF L-GLUTAMINE?

L-glutamine, like all amino acids, is a protein building block. It’s made in the muscles (in amounts often referred to as “abundant”), and the body uses it for a variety of things—like immune system function and digestive issues.

Amino acids are often believed to help build and retain muscle in the bodybuilding world and to recover from training, and much of l-glutamine’s draw in the fitness world comes from similar reported anecdotal experiences.

Go-to trainer Will Torres first tried it 15 years ago, but the current buzz inspired him to use it again to help him recover from his own high-intensity exercise schedule.

“I feel like my mood has improved, I am more rested when I sleep, I don’t need caffeine to get going in the morning. Now, I feel like I’m recovering a little better, and a little faster, and my body feels better prepared for the next work out,” he reports.

Barry’s devotees agree.

THE SCIENCE

Research so far, however, has not verified l-glutamine’s reputation as a workout booster. Two small studies on weight lifters showed no improvement in performance or muscle retention, and little to no research has been done on its ability to help regular fitness-goers recover from exhaustive training. For serious endurance athletes, the main benefit that’s been demonstrated is that it can help boost the immune system, preventing infections that often occur because of the exhaustive nature of training.

“The average gym goer doesn’t need l-glutamine,” says Middleberg Nutrition founder Stephanie Middleberg, MS, RD. “It’s suggested that it helps boost the immune system for those intense athletes, like marathon runners, but in healthy people, it should be producing naturally in the body in a sufficient amount.” That’s not to say that this increasingly trendy amino acid is going anywhere. “Any protein is always of interest to those who want to stay fit, lean, and healthy,” explains Middleberg.

If you do choose to try l-glutamine based on the reported benefits, Middleberg says to take it on an empty stomach and after a workout when your levels are likely lower. (Although there are no known toxic levels, avoid taking more than 30-40 grams daily.)

Or you can order a green juice or snack on a hard-boiled egg—both natural sources of l-glutamine—while you wait for more scientific studies to come in. —Amanda Benchley

Have you taken l-glutamine? Tell us your experience in the Comments, below.