Do without it

Reading is to the mind what food is to the body. if you try to do without it, you simply cannot. On the other hand, if you try to read more than your system can absorb, you can easily lose your appetite for reading. You must remember, therefore, that your mind is no less sensitive to injury than your body.

In the above passage, what does "it" refer to in the second sentence?

I think that "it" refers to "reading".

But someone says that "it" refers to "mind", because "do" refers to "read".