Glutamate: Can It Be Use To Your Advantage? Study Shows Insulin Sensitizing Effects of Dreaded Food Additive

"Now you've got me confused!"

In the context of MSG scare, glutamate has gotten such a bad rep that it seems highly counterintuitive to assume that there was anything good about the major excitatory amino acid in the human body and still, a recent study from the Department of Kinesiology at the University of Waterloo clearly suggests that "MSG and carbohydrate supplementation can be used to manipulate plasma glutamate" (Sebastiano. 2013)... and no, we are not talking about an in-vitro or rodent study here.

With 9 perfectly healthy, recreationally active men aged 23.9+/-1.9y and a BMI of 25kg/m² the results can however be taken as being representative for at least large parts of the ever-decreasing number of "normal-weight" individuals.

There is a potential string attached

Usually, the "on the other hands", are something I am talking about at the end of the article, but in this case, of which I expect that it's going to become pretty controversial it appears prudent to address them right away: there was a hitherto unexplained dichotomy in the insulin response of the 9 subjects after the ingestion of the 150 mg/kg body weight MSG or placebo capsules, the subjects ingested after an overnight fast and 30 minutes before they consumed a 75 g carbohydrate or a non-energy placebo drink.

Figure 1: AUC for glucose and insulin across the trials (left); serum insulin and glucose concentrations in the post-prandial period during the glutamate and no-glutamate trials (Sebastiano. 2013)

What looks like a Taubs'ian nightmare is actually nothing but a perfectly normal insulin response to the ingestion of 75g of carbohydrates. In a healthy individual, the insulin response is proportional to the influx of glucose from the digestive tract and ensures that the latter is getting stored in muscle, liver and fat (with the former being topped of first, cf. figure 3 in previous article).

On average, we do the the same if not less insulin with a greater reduction in glucose

That being said, there is no debating that contrary to the scientists' working hypothesis, the average insulin secretion was not on augmented in the GLU+CHO, while the onslaught of glucose was significantly reduced (see figure 1, bottom right) compared with the CHO only trial.

Epidemiology paints a different picture of MSG (learn more)

"[I]t appears that glutamate, when combined with carbohydrate, elicits one of two insulin responses, depending on the individual.

Although the present study was not designed to explore this question, we did remark that the differences between these two groups of participants were not explained by factors associated with glucose handling, such as habitual activity levels (assessed using the Baecke questionnaire), fasting glucose, available glutamate or insulin sensitivity." (Sebastiano. 2013)

Now this is quite astonishing as it would suggest that the co-ingestion of glutamate does actually improve the insulin sensitivity only in some. In those the effect must yet have been so pronounced, though, that the "non-responders" didn't carry any weight...

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Apropos weight, in order to confirm whether or not you can use glutamate to your advantage, we would need at least two follow up studies:

Will the additional butter on top of the potatoes reduce the insulin response? Learn the answer to this other questions in one of the famous installments of the "True or False?" Series on the SuppVersity (learn more)

• One study to elucidate the long-term consequence of the addition of glutamate to every (high) carbohydrate meal in healthy human subjects (the hypothesis would be that we should lower HOMA-IR and HbA1C levels as a sign of improved glucose metabolism).

• And another study to make sure that the obvious insulin-sensitizing effects glutamate appears to exert in at least some subjects are not adipose-tissue specific - or, in other words, that it is not an increase in fatty acid synthethase and subsequent storage of glucose as fat that's behind the significantly reduced glycemia the scientists observed.

What? You think all that is bullocks, because "we all know" that glutamate is going to make you fat? Well, in a non-calorically controlled scenario this may still be the case.
To understand that you will however have to get rid of your false prejudices against insulin, the release of which also acts as a satiety signal (in the insulin sensitive individual) and will have you stop eating (Verdich. 2001). With your glutamate laden super size fast food menu, your body may not even recognize that you have just been downing a Big Mac, XXL French fries and an XXL Coke, estimating that the stuff you ate was probably a Happy Meal with only 50% of the calories. In other words, in the real world, McGlutamate and ChinaMSG are probably still not the best places to dine regularly ;-)

References:

• Di Sebastiano KM, Bell KE, Barnes T, Weeraratne A, Premji T, Mourtzakis M. Glutamate supplementation is associated with improved glucose metabolism following carbohydrate ingestion in healthy males. Br J Nutr. 2013 Jun 11:1-8. [Epub ahead of print] 
• Verdich C, Toubro S, Buemann B, Lysgård Madsen J, Juul Holst J, Astrup A. The role of postprandial releases of insulin and incretin hormones in meal-induced satiety--effect of obesity and weight reduction. Int J Obes Relat Metab Disord. 2001 Aug;25(8):1206-14.