A daily L-glutamine dose of 30 grams per day was associated with a significant reduction in the ratio of Firmicutes to Bacteroidetes in obese and overweight people. The Firmicutes/Bacteroidetes ratio is a good biomarker for obesity, said the researchers.
“The finding that L-glutamine promotes changes in the gut microbiota composition provides support for the importance of some nutrients in modulating the intestinal bacterial profile,” wrote the researchers in Nutrition. “These changes resembled the weight loss programs established in the literature.”
Gut health and obesity
The study adds to emerging body of science supporting the effects of gut microflora on metabolic factors and obesity.
A 2005 study by Jeffrey Gordon and his group at Washington University in St. Louis indicated that obese mice had lower levels of Bacteroidetes and higher levels of Firmicutes, compared with lean mice.
One year later and Dr Gordon’s reported similar findings in humans: The microbial populations in the gut are different between obese and lean people, and that when the obese people lost weight their microflora reverted back to that observed in a lean person, suggesting that obesity may have a microbial component (Nature, Vol. 444, pp. 1022-1023, 1027-1031).
A more recent paper from the same group in Science Translational Medicine (Vol. 3, 106ra106) reported that ingestion of probiotic bacteria produced a change in many metabolic pathways, particularly those related to carbohydrate metabolism.
The new study, albeit small scale and of limited duration, suggested that the amino acid L-glutamine may also have weight management potential by changing the bacterial composition in the gut.
The Brazilian researchers did not observe any changes in body weight during their 14 day study, but noted that a longer intervention period “may result in metabolic changes”.
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.
“In addition, increased abundance of the Prevotella genus has been described as a shield against inflammation and non-infectious diseases of the colon. After L-glutamine supplementation, but not after alanine, we observed an increase in Prevotella, suggesting that L-glutamine may have a protective effect on the gut via modulation of bacteria.”
Published online ahead of print, doi: 10.1016/j.nut.2015.01.004
“Oral Supplementation with L-Glutamine Alters Gut Microbiota of Obese and Overweight Human Adults: A Pilot Study”
Authors: A.Z.Z. de Souza, A.Z. Zambom, K.Y. Abboud, et al.