My neighbor is a strict vegan, and refrains from any animal product at all.
So not even fish or eggs?
Nope. No meat, eggs, dairy, fish, or other meat derived product.
Wow - does it affect his body in a negative or positive way?
It has actually made him healthier. A well-planned and balanced vegan diet can reduce the risk of some types of chronic diseases.
Was he unhealthy before he switched to be a vegan?
No not really, but he says he feels healthier and has energy.
Did he switch for religious reasons?