That sounds like it would be a tough case! I would guess there would be some way to get the nutrients to the person- the vitamins and minerals as well as the calories- possibly IV, I'm not sure though.
That's how I used to feel about food and it turned out I had Celiac disease. Once I got tested and then got off gluten (and for a while also dairy), and took L-glutamine for a month to heal my gut, then I could start feeling better. He should get tested for Celiac disease. If he doesn't have that, then get tested for other food sensitivities. My boyfriend is allergic to all fruit. If you are bitten by a certain type of tick, you are allergic to meat for about 1-2 years. There are many kinds of food allergies and sensitivities. Always avoid chemicals by buying organically grown foods.