Can eating nutritional yeast give you brain fog?

There are several different factors that contribute to brain fog during fasting or FMD, and many people experience it at some point during any low-calorie or ketogenic diet. The nutritional yeast in the diet is glutamic acid, and is used for flavor and texture, in addition to playing a vital role in your nervous system. There is no medical research demonstrating true allergies to glutamic acid, and more research is needed, but for those who are sensitive to glutamate or MSG, the consensus is that the small quantity of glutamic acid in the diet is unlikely to trigger a reaction.