a vetetarian diet,is perfectly able-depending on each persons differing food needs,though unfortunately it wont work for all of us.
-woud always recomend seeing a dietician before making such a big diet change,especialy long term as it will at the very least affect iron,vitamins and protein-unless are well skilled on knowledge in how to get those things without meat/dairy etc.
had personaly become very ill from being on a vegetarian diet due to already being severely restricted in food [directly and indirectly by autism],survived on roast or fried potatoes and vegitarian friendly gravy,had the ocasional fish fingers if remember corretly...it really affected health-gave up after exactly one year as had found mum had been secretly stashing meat fat in the gravy so it had all been a big con anyway.
-have been on a prescription liquid food for years called ensure,thats possibly an option for vegitarian americans...
have ever been spoken to by the gastro docs about a high nutritional liquid food? it sounds like are very restricted and something like that might be worth enquiring about to them or a dietician.