I worked with a woman who was a vegitarian a number of years ago. She was out sick a total of 35 times in three months. Was always getting a cold or some such other ailment.
I think it’s hard for vegans to get high enough quality and variety and ENOUGH protein.
Good quality proteins are absolutely essential for the immune system, which is creating and diposing of cells and chemical messengers by the truckload.
I had a vegetarian boss at one time. He was perpetually sick and he finally got a cold that just wouldn’t go away even after he went to his naturopath at read the latest vegan diet book.
I finally got tired of his coughing, sneezing, and whining and told him to go home tonight and eat a steak.
He actually did and came in the next morning and told me he felt much better and had much more energy.
He looked much better and had more color in his face. He had a classic case of anemia.
He seemed much happier after that.