[blueash]

Please don't over interpret the opinion of one doctor as to what is causing person's friend's symptoms. This does not sound like evidence based medicine and would fall into the definition of "alternative". Very restricted diets that can only be developed after doing many tests are potentially dangerous. Humans are meant to eat a wide variety of foods. Sometimes the supratentorial aspects of diet and nutrition overwhelm the science.
It won't make any likely difference, but... grape seed extract won't work. Go online and look it up. The"natural" websites talk about using grapeFRUIT seed extract mixed with vinegar (not water), never alone, to clean produce. It is the vinegar (acetic acid) which has some benefit. Grapefruit is also an acid (citric) but I have no idea if the acid is present in a seed extract.