A Low Glutamate Diet Improves Cognitive Functioning in Veterans with Gulf War Illness, 2020, Kirkland et al.

Now I feel a few things are mumbled together.

Glutamine can be turned into glutamate, but also the other way around.

If a "high glutamate diet" equals a high processed diet, more things are changed when reducing glutamate than "just" reducing glutamate. You could potentially have high glutamate in your body without eating MSG, because your metabolism makes it so.

If you react to a supplement like L-glutamine, it could just mean that you have enough of it in your body, so extra supplementation can be detrimental (or best case it makes no difference), while someone else have lower levels and thrive on said supplement. Some metabolites are dependent on the rest of your diet, how well you absorb and metabolite nutrients (which again are dependent on multiple things) etc., "subtypes" could just be an effect of different diets, not necessarily different disease mechanisms.

 

Many react to fermented foods due to histamine, it's not straightforward in the least to figure out *what* in the food one is reacting to. There are the obvious candidates, but could also be something else. Gets even worse if it's a group of similar compounds you can find in many foods. Or many different compounds could have similar effects (there are a lot of things that can be either protective or detrimental to the gut lining for example, makes me so annoyed when someone creates a muffin to test non celiac gluten intolerance and said muffin contains other flours or gums that could influence the gut wall and give symptoms just like gluten..)

Nutritional sciences are - thankfully - moving towards a focus to dietary patterns and whole foods, not just looking at individual nutrient. Foods contain many compounds in addition to the one nutrient we are interested in learning more about, some could be protective against an otherwise harmful substance, while others could be harmful we just don't know it yet. Taking a supplement is thus not the same as getting the same nutrient from food ( i) missing the other substances that would otherwise have been ingested with the nutrient ii) dosage may be higher/lower than what you would get from food and the body might not metabolize it well).