Final answer:
The metaphor 'new ideas are food for his mind' compares the consumption of ideas through reading to the nourishing effect that food has on the body, emphasizing the reader's intellectual growth and hunger for knowledge.
Step-by-step explanation:
The metaphor 'new ideas are food for his mind' suggests that just as food is necessary for the body's growth and nourishment, new ideas serve a similar purpose for the mind. When we say that someone reads incessantly, it can imply a deep passion or need for reading, similar to a hunger. Feeding the mind with new ideas represents the reader's quest for knowledge, understanding, and intellectual satisfaction.