Gluten-Free Diet. A gluten-free diet is critical for people with celiac disease, which means that the ingestion of gluten triggers an autoimmune attack of the intestinal lining, causing gastrointestinal distress and the potential malabsorption of important nutrients. About 1 percent of the population suffers from celiac disease, and about 10 percent have a less specific sensitivity to gluten, according to Mayo Clinic. Advocates claim that a gluten-free diet can ease a number of ailments, including digestive problems, eczema, chronic fatigue, headaches, infertility, ADHD, autism, depression, chronic inflammation, thyroid disease, weight gain and diabetes. Following a gluten-free diet means steering clear of wheat; barley; rye; triticale, a mix of wheat and rye; seitan, an Asian food made of gluten; and oats, since they're vulnerable to contamination with gluten. You'll load up on fruits and vegetables, meat, dairy, poultry, fish and eggs, as well as a growing selection of specifically designed gluten-free products. Because of the gluten-free diet's increasing prevalence, U.S. News is providing exhaustive information about what it entails, but is not ranking it since the diet is designed for medical purposes.