|Image 1: Don't do this at home. A pig with cannules that have been dug into its digestive tract to study chemical enzymatic and microbial actions (University of Illinois)|
"Hey, you gut bug, leave my arginine alone!"
It has been known forever that l-glutamine is the most abundant amino acid in the body. It's sheer ubiquitousness and rapid turnover relfect its crucial role in whole body nutrient metabolism and health. While fitness and health enthusiasts have long been mislead to believe that glutamine would exert direct ergogenic effects (cf. Amino Acids for SuperHumans: Part IV - Glutamine), scientists and laymen alike are now zoning in on its protective effects on the integrity and function of the small intestine. In this context it has recently become clear that
... AA [amino acid] metabolism in the small intestine plays important roles in the regulation of whole-body AA homeostasis. [...] Recent studies suggest that bacteria in the small intestine are active in the metabolism of AA, especially lysine, threonine, arginine, glutamate and glutamine. The rapid utilization and metabolism of glutamine by small-intestinal bacteria supports the view that glutamine is a key regulator of the survival and growth of bacteria in the intestine through the regulation of the bacterial metabolism of nitrogenous compounds particularly AA.The usage of glutamine by your gut bacteria is yet not the only physiologically significant interaction between dietary glutamine and the billions of microorganisms in your gastrointestinal tract. According to Dai et al. glutamine may also affect the utilization and metabolism of other amino acids by small-intestinal bacteria "and metabolism in small-intestinal bacteria, and thusly influence the "the production and profile of nitrogenous compounds in the lumen of small intestine and whole-body amino acid homeostasis."
Complex interactions with a simple solution? Ramp up your glutamine intake!?
As you can see in figure 1 the influence of dietary glutamine on the uptake of nitrogen amino acids by Streptococcus sp., Escherichia coli, Klebsiellasp. and a number of jejunal mixed bacteria or ileal mixed bacteria from the small intestine of pigs (as omnivores they have a very similar digestive tract as humans) was profound, yet dose depended and overall pretty complicated.
|Figure 1: Change in utilization [nmol /( 10 cells 3h )] of amino acids from the l-arginine family by small intestinal bacteria subsequent to incubation with 0, 0.5, 1, 2 and 5 mmol/L l-glutamine (data adapted from Dai. 2012)|
|Figure 2: Change in utilization [nmol /( 10 cells 3h )] of branched-chain amino acids by small intestinal bacteria subsequent to incubation with 0, 0.5, 1, 2 and 5 mmol/L l-glutamine (data adapted from Dai. 2012)|
Species, dosage and amino acid dependence - further investigations necessary
If you take a look at all the data from the Dai study, it is immediately evident that things are way more complicated than a cursory look at the graphs in figure 1-2 would suggest:
- the net effect on the metabolism of amino acids from the arginine-family is particularly pronounced; the production / conversion of arginine to ornithine and citrulline increased and the overall use of arginine by the bacteria decreased (in some cases profoundly)
- the increased glutamate production from E. coli could be of particular importance, in view of the multi-faceted function of glutamate in the mammalian (and thusly human, as well) metabolism
- the decrease in the utlization of BCAAs, but also the amino acids from the serine aspartate family, i.e. l-alanine, l-asparagine, l-aspartate, glycine, l-serine and l-threonine allow for a greater uptake and utilization of these physiological important amino acids by the enterocytes
Illustration 1: Potential gut microbiome mediated benefits of higher dietary or supplemental l-glutamine intake; maybe it's still worth taking although it's not a proven ergogenic
- the thusly well-nurished and healthy gut lining protects the host (you) from bacterial invasion and infection
- with their role in the intestinal signaling pathways, the increased availability of arginine, amino acids from the arginine family and their related metabolites like agmatine and polyamines can exert direct regulatory effects on gut function and integrity
- there is emerging evidence that the degradation of serine and aspartate, which was reduced in the presence of larger amounts of glutamine, is a major factor contributing to the (over-)colonization of the small intestine with bacteria and the production of virulence factors in the intestine