By 1930, Price had shifted his interest to nutrition. In 1939, he published "Nutrition and Physical Degeneration", detailing his global travels studying the diets and nutrition of various cultures. The book concludes that aspects of a modern Western diet (particularly flour, sugar, and modern processed vegetable fats) cause nutritional deficiencies that are a cause of many dental issues and health problems. The dental issues he observed include the proper development of the facial structure (to avoid overcrowding of the teeth) in addition to dental caries. This work received mixed reviews, and continues to be cited today by proponents of many different theories, including controversial dental and nutritional theories.