At the Common Ground Fair, a wise consumer asked me about the MSG contained in nutritional yeast (she also sent me this article on its dangers). I didn’t have an answer then, but I want to have an answer now.
The short answer is yes, nutritional yeast contains free glutamic acid.
MSG, synthetically produced glutamic acid, contains both L- and D-glutamic acid. For comparison, imagine two different gloves, a left glove and a right glove. If your body can only process left gloves, having a lot of right gloves roaming around will produce serious problems. What can happen with too many extra gloves? The leftover, wrong “gloves” in Tylenol are what can cause liver failure and birth defects.
So, while nutritional yeast (and pretty much most cooked or processed foods with anything fermented or full proteins) contains free glutamic acid, it isn’t clear whether that has the same effect as MSG in the body. Could it? Maybe.
If the MSG gets into the body, very bad things can happen. When it is injected into the body: “poly-D-glutamic acid (molecular weight, 20 kd; 250 mg/kg/day subcutaneously for 1 to 4 days) produces an acute thesaurismosis in the proximal tubular cells associated with a marked proliferation of peritubular interstitial cells in rat kidney” In English? The D-glutamic acid fried the kidneys. (study here).
But does MSG get into a healthy gut?
“Dogs (n = 10) and humans with psoriasis (n = 21) orally administered L-AMT and L /D-AMT at the same L-enantiomer dose resulted in stereoselective absorption (absent D-enantiomer in plasma) (study here). In English? In healthy guts the D-glutamic acid is not absorbed. That’s right, it doesn’t get through the gut wall.
In a genetically susceptible gut or an unhealthy gut, the D-glutamic acid might well get through. In which case, MSG wreaks havoc. It might also act in the gut to really upset the gut flora. There are studies that show D-glutamic acid can do bad things to bacteria. Breakdown those bacteria in large quantities, and you can have a problem.
So, should we avoid all glutamic acid containing products on the outside chance? No.
First, the group of products is very, very large and overlaps healthy foods.
Second, foods containing the breakdown products taste very good. Better than products containing MSG. “Four of the seven cooked meat products developed had a significantly higher content of umami-contributing compounds compared with the control. All products, except those containing MSG or tomato puree, were scored (by trained sensory panel) perceptually significantly higher in umami and/or salty taste compared with the control.” (study here). If we’re going to respect the body’s wishes, the body can tell the difference between good and bad glutamic acid.
Third, there’s a reason the body likes that taste. “YH (yeast hydrosolate) groups showed improvements in Beck Depression Inventory and Beck Anxiety Inventory scores after YH administration for 2 weeks. Treatment also seemed to have a more significant (P < .05) impact on the somatic manifestations of anxiety as indexed by the Beck Anxiety Inventory scores. Food materials used as a source of YH have been found to be associated with increases in alertness and adaptation to stress.” (study here) That’s right, the same things that might cause a problem can definitely help with the stress response.
From personal experience, MSG is a very bad thing. My own response to it is to develop eye blisters. (Really. It’s so much fun.) I most recently discovered the hard way that Hannaford peanuts now contain added MSG. But unlike added MSG, nutritional yeast has never given me eye blisters. So I would have to say all glutamic acid is not the same, and most of us shouldn’t worry about the free glutamic acid in naturally fermented foods.