Not too much.
Food Rules doesn't really offer much that In Defense of Food does not, but it is much shorter.
One thing that annoyed me was that Pollan perpetuates the myth of food combining. He states that beans eaten with corn will supply amino acids missing from corn and therefore create a complete protein. In fact, vegetables and grains all have complete protein and do not need to be combined in the human diet. It is important to eat a wide variety of foods, but that is not for the reason of protein complementarity. Scientists debunked the food combining myth decades ago.