Why would any of these body parts go by the wayside? Teeth aren't muscles and don't require exercise, so it's not like they'd atrophy. His stomach, liver and intestines are all involved in the digestive process which is still required for the body to synthesize useful proteins out of the things he's ingesting, whether it's "real" or not. Kidneys are involved with waste removal which, true, wouldn't get as much use as a result of him not taking in as much waste material, but he's clearly still going to have waste material from his body, albeit perhaps not as much. Even if you drink nothing but water the body still filters it out as urine which is a major function of the kidneys. Do you think it'd be detrimental to the body to only ingest his concoction? Why?

He can still eat socially, he says so in the interview. That said, does one need to eat in order to socialize with friends and family? You can still sit around drinking nutrient-slush and enjoying company every bit as well as a roast turkey and potatoes, couldn't you? As for bringing his own... what do vegans do? What do people with allergies do? Peoples' lifestyles are already a lot more varied with regards to diet than they were a few decades ago. Can we really fault him for not just eating what everyone else eats?