Brain fog sometimes is caused by different reasons.
My brain fog comes from my traumatic brain injury. The injury was in the right frontal lobe as well as some damage in the occipital -
My doctor who was a TBI survivor also, told me about a study done at Mass General; all refined sugars and all foods that can be made into alcohol, like rice, wheat, potatoes,etc is removed. The theory is that when the body digests these foods, the fermentation of them is recognized in error by the brain as alcohol and thus gives you that brain fog. I do not eat any of these foods and replace breads with wheatberry products; honey, agave and evaporated cane for cooking. Proteins are added to enhance the brain alertness.
I works! Have lived like this for six years and if I 'cheat' I know it.