Are there any medical conditions which require someone to eat flesh?
Are there any that prevent someone from being vegan?
There are certainly people who feel like their health suffers when they don’t eat meat, unfortunately.
As I’ve posted about recently, there are some conditions which might make it difficult to eat a normal vegan diet, such as having herpes, being allergic or intolerant of soy or wheat, and having trouble absorbing iron.
And although research shows that a plant-based diet is a good way to treat early chronic kidney disease, once someone has to be on dialysis it can be difficult. This is because most plant foods are either high in phosphorus (as is dairy) or potassium. People on dialysis tend to need large amounts of protein and it’s hard to get it from plants without also getting phosphorus. You can take calcium tablets to try to prevent phosphorus absorption but this strategy is limited.
Vegetarian Diet for Kidney Disease Treatment, by Joan Brookhyser, RD, CSR, CD, is a book about how to be vegetarian or vegan while on dialysis. So, it can be done but I do not know how often it is done.
Finally, there might be some people whose bodies don’t make enough of a nutrient that can only be obtained, at this time, from animal foods.
I once corresponded with an animal advocate who thought his body did not produce enough cholesterol and it was causing him to pass out. He did have very low cholesterol (under 100 mg/dl) which may or may not have been the problem. He said that when he ate cheese, he felt much better and didn’t pass out. We tried to figure out what else it might be, such as not enough calories or fat, but we did not succeed. However, I do not think that cheese, or any other animal product, has magical properties. If the cheese really was solving his problem, then there must be some molecule(s) in the cheese that can be uncovered as the cause.
Eventually, we might be able to produce all such molecules without harming animals, particularly if in vitro meat becomes a reality.