Vegetarian got sick after eating meat
Question: Hello spot. I have been eating a strict vegetarian diet for the last three months. Last night my husband and I shared a plate of spaghetti with meat sauce at an Italian restaurant, thinking I would make just this one exception to eat meat. I got extremely sick to my stomach, vomited, and had diarrhea as well today. Did the meat make me sick? My husband is fine, so I don't think it was food poisoning. Will my body no longer tolerate meat?
Answer: The enzymes from the pancreas that digest protein are used to digest all proteins, not just those from meat. And even people who eat no flesh are digesting "meat" all the time, in the form of sloughed off cells of the gut. This contributes a significant amount of protein to the body each day.
The protease enzymes from the pancreas are "inducible," meaning they are only produced in the quantity that is needed for the person's typical substrate load. If a long time vegetarian were to start eating external meat again which resulted in more protein than was typical for them, they might want to do it slowly. It may take 3-4 days to get their enzymes up to speed. The enzymes have a short half life and will drop back down to the lower level quickly if protein consumptions drops again.
If you've only been on your strict vegetarian diet for three months and you shared a plate of spaghetti with your husband, I would wager that your body's unpleasant reaction didn't have to do with your body's inability to digest the meat. What's more likley is that there was something else in the food that made you sick, or that you were getting sick from something you ate earlier in the day that your husband did not eat.
— April 17, 2005