If I hadn't eaten salad I might have starved! I lost my taste buds and salad was one of the few things that tasted of something, anything! Actually tasted like salad! I ate lettuce, cucumber, tomato, avocado because I could taste them all.
I can only imagine this is to ensure you are not exposed to any unhelpful bacteria when your immune system is being hammered, so same precautions. Wash everything thoroughly, even the skin you are going to peel off, even if the package says it's pre-washed! Ditto fruit. I had no problem, but perhaps anyone who has can comment too? Best of luck!