"Glutamine is the most abundant amino acid in muscles. We need it to improve and maintain muscle size and strength and to produce the anti-anxiety neurotransmitter gamma-aminobutyric acid (GABA)," Zembroski says. GABA helps calm your nervous system. When you're deficient in GABA, it can lead to anxiety, OCD, and restlessness. "Grass-fed whey protein is an excellent source of glutamine. It is readily available and a great protein source for your post-workout shake," Zembroski says.
If you don't do protein shakes, he says other ideal sources of glutamine are low-mercury fish, organic chicken, eggs, walnuts, and wheat germ.