Author of a million copy bestseller published in the 1980s and The Yeast Connection Handbook, which provides new information for the 21st Century.  In addition to yeast-related health problems, he spoke passionately about the role of nutrition in children's hyperactivity and learning disorders.

The author of 14 books and numerous articles in medical and lay literature, Dr. Crook addressed professional and lay groups in 39 states and eight countries. For 15 years, he wrote a nationally syndicated health column for General Features and Los Angeles Times syndicates and was a popular guest on national television and radio programs, along with the BBC and other international networks. Many of his publications have been translated into French, German, Japanese and Norwegian.