@bayhorse There are foods that I have found that are off limits in general for those following a low glutamate diet:
Aged cheeses (like Parmesan and Roquefort).
Processed meats and slow-cooked meats.
Cured ham.
Certain seafood like scallops and oysters.
Vegetables:
Mushrooms (especially shiitake and porcini).
Tomatoes and tomato sauces/pastes.
Peas.
Fermented foods:
Soy sauce and other Asian sauces (like fish sauce, oyster sauce).
Miso.
Yeast extracts and similar products (Marmite, Vegemite).
Other foods:
Nuts (walnuts, cashews, peanuts).
Bone broths.
Grapes and grape juice.

These are the worst offenders, but ultimately all food contains glutamate. "Savory" foods contain the highest levels of glutamate. The stronger the flavor, the higher the glutamate level tends to be. Also, older food that has been sitting in the fridge or fruit on the counter contains higher levels of glutamate.... Fresh is best! There is a government website available that lists the most common foods and their glutamate content. The idea is not to eliminate all glutamate -- which is impossible and would be dangerous. Each person needs to learn which foods they react to and keep (rough) track of how much glutamate they consume in a day, being mindful of portions and figuring out which foods and combination of foods they are okay with, and which they are not. I can eat small portions of high glutamate foods, for example cod, almond butter, baby spinach (not full grown), etc. I'm hoping I'll be able to tolerate baby tomatoes in the future as I understand there is less glutamate content in those than full size tomatoes.

When researching glutamate, histamine often comes up-- high glutamate foods are also high histamine foods. I wondered if perhaps I had a problem with histamine but I believe it truly is glutamate because I react with worsening symptoms when I am given a steroid to try and knock out inflammation. Steroids drastically increase glutamate levels but decrease histamine levels. Both histamine and glutamate can cause similar issues but it is often difficult to tell which a person has trouble with. Interesting stuff.

I had been eating fermented foods, yogurt, and bone broth to try and heal my intestine from the damage caused by Celiac Disease. I was also eating a lot of fish like sardines thinking that the Omega 3s would be good for my brain (that I knew had been under attack from Celiac causing bouts of paralysis etc). I loved natural peanut butter, and protein rich foods. I thought I was doing the right thing but I was eating and drinking all of the wrong things. These are all healthy foods for so many people, and I do not want people to be afraid to eat them! But I feel there needs to be an awareness about this problem, especially if there are known gut issues or brain issues.

I hope this might be helpful to someone. It is so hard to not feel well and not know why. I am so grateful that a change in my diet has helped me so much. I wish everyone all the best on their health journey.