Symptoms like abdominal pain, bloating and diarrhea are often associated with the ingestion of lactose, fructose or gluten containing nutrients. The prevalence of lactose intolerance, fructose malabsorption and celiac sprue is quite high. If the symptoms are interpreted in the right way, the diagnosis and the treatment are easy. The ingestion of lactose or fructose containing food leads only to unpleasant symptoms, but in gluten sensitive patients an inflammation and destruction of the small intestinal mucosa develops. The consequences are an impaired absorption of macro- and micronutrients with their specific symptoms. The patients with lactose intolerance and fructose malabsorption can avoid the symptoms if they stick to a low lactose or fructose containing diet. On the other hand, patients with celiac sprue need a life-long gluten-free diet to heal the mucosa, to ameliorate the symptoms and to avoid relapses.