As mentioned before, brain fog has different causes, it can be caused by the food you eat or low-quality sleep. You should avoid unhealthy foods to take care of your mental state, like artificial sweeteners and refined carbohydrates, food that contains monosodium glutamate (MSG), alcohol, and others.
Citric acid's most common use is as a food preservative. Industrial citric acid is one of the most used additives in the world. It is used for flavor enhancement, ingredient preservation, and boosting acidity in order to avoid o protect consumers from botulism; a rare but severe illness caused by Clostridium botulinum, a toxin-producing bacteria.