The researchers recruited 33 overweight and obese adults, aged between 23 and 59 and randomly assigned them receive supplements of L-glutamine or L-alanine for two weeks.
Results showed that the L-glutamine group exhibited statistically significant differences in the Firmicutes and Actinobacteria phyla compared with the ALA group.
A reduction of 0.3 was observed in the ratio of Firmicutes to Bacteroidetes ratio in the L-glutamine group, they added (from 0.85 to 0.57), while L-alanince was associated with an increased from 0.91 to 1.12.
"Thus, these findings suggest that oral supplementation of L-glutamine have similar effects on gut microbiota as weight loss," said the researchers. "We would like to highlight that although the age range of the volunteers was large (23-59 y) and aging may have an effect on intestinal microbiota, the results obtained in this study were statistically significant."
Commenting on a potential mechanism, they noted that L-Glutamine supplementation may reduce pro-inflammatory cytokines. "Some bacteria genera are associated with gut inflammation," they wrote. "For example, increased levels of Veillonella are associated with higher levels of gut inflammation and the development of colitis and Crohn's disease. In our study, the number of bacteria from the Veillonella genus reduced after L-glutamine supplementation, suggesting that L-glutamine may have an anti-inflammatory effect, at least in part, due to the decrease of this genus.