'The age-old saying goes "you are what you eat," but one doctor is out with a new book that is taking that notion a step further, arguing that some foods you eat can help you beat disease.

Dr. William Li talked about his new book, "Eat to Beat Disease," in an interview with "Good Morning America," saying we have completely underestimated the role that the foods we eat can play in combating illness. Plus, he shares his top five foods to go for the next time you hit up the supermarket.'

See the full clip on: Good Morning America