And later in the book he goes into further details on each of these foods and the health benefits science is now showing are associated with eating them. One point he dwells on is the distinction between clean and unclean meats. He notes some of the health problems that have been caused by people eating unclean meats. He also includes an interesting chart of clean and unclean meats. Besides each kind of meat is an indication of it's toxicity level.
All clean meats have much lower levels of toxins than unclean meats.
However, these toxicity levels are taken from a study done in 1953. It would be helpful if a more recent study were cited. In regards to the second principle, he first enlarges it beyond food to look at what God said about aspects of healthy living besides food. He notes that God's directives in regards to personal hygiene and sex give health benefits to the person following them. Then Later he looks at foods.