This week on Health & Longevity, Dr. John Westerdahl's featured guest is Michael Greger, M.D.; Physician, author, and internationally recognized speaker on nutrition, food safety, and public health issues. Dr. Michael Greger discusses gluten and gluten-free diets. What is gluten?  Is it harmful, harmless or healthful?  Who really needs to be on gluten-free diets? Dr. Greger discusses the scientific realities as well as the myths concerning gluten.  He is the host of the very informative website on nutrition and health issues, www.NutritionFacts.org.