It's just that your body stopped making the enzymes that digest meat. It'll start making them again if you eat meat regularly for awhile (or any animal based protein), and then you can back off to once a week or so, or less often. Just make sure you occasionally have animal based proteins (and they're all quite different from each other... it's one reason why american's get so sick eating goat... the proteins are different than chicken, cow, pig that most are used to). ANY kind of digestive enzyme (specific to animal proteins) will help with the others (a meat eater eating goat doesn't get as sick as a long time vegetarian eating goat or mcdonalds).
Actually... that's a good idea. Fast food is *almost* predigested for you. It's incredibly good for sick people (and often the first "this is going to suck" meal that former vegetarians have). Same token, eating meat that has been "tenderized" with enzymes will also ease you back in.
To keep up your enzymes without actually having to *eat* meat, try bouillon. Boil carrots in chicken stock... or add to mashed potatoes instead of butter. Add some beef stock to a soup. Miso soup is a smoked fish based soup. While, yes, in order to have animal proteins they are all animal based... it's an easy way to keep up your enzymes without actually having to eat lumpia or a steak.