Gastroenterology Associations

Canadian Association of Gastroenterology   
American Gastroenterology Association
American College of Gastroenterology
American Association for the Study of Liver diseases
Canadian Association for the Study of the Liver
Canadian Digestive Health Foundation

Inflammatory Bowel Disease

Crohn's and Colitis Foundation of Canada
Crohn's and Colitis Foundation of America

Irritable bowel syndrome

myginutrition (low FODMAP diet)
​​about ibs (International Foundation for Functional Gastrointestinal Disorders)
bad gut (Canadian Society of Intestinal Research)

Celiac Disease

Canadian Celiac Association
Fondation québécoise de la maladie coeliaque

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The NIDDK is a fantastic web site that offers good explanations and descriptions of many digestive diseases.