Has he ever thought about doing a liver cleanse? Milk thistle, chamomile, and turmeric are great for the liver.
As for foods/beverages to avoid, do not consume anything with alcohol or HFCS. I find that honey, which is very high in fructose, maple syrup, molasses, and artificial sugars that end in "itol" are also hard for my liver to digest.
Some medications are also hard on the liver.