An intolerance is often due to an enzyme deficiency (as opposed to allergy which is an acquired immune response). Testing for this is cumbersome and the diagnosis is usually made by a food elimination diet.
Alcohol Intolerance: Common amongst Asians (especially Chinese, Japanese, Korean) and related to ALDH2 deficiency. Flushing is the most common symptom but others include sleepiness, nausea and vomiting. ALDH2 deficiency is also linked to esophageal cancer in those with it who do drink alcohol.
Hereditary Fructose Intolerance is a rare but life-threatening condition that presents in infancy. Milder forms may not be diagnosed until adolescence or adulthood.
Dietary Fructose Intolerance is much more common and related to malabsorption of this fruit sugar. The amount of fructose consumed is more than the small intestines can metabolize and absorb resulting in abdominal pain, bloating, gas, nausea and/or diarrhea.
Fructose is found in nature in 3 forms:
Free fructose in fruits and honey.
Disaccharide form in sucrose (broken down to glucose and fructose).
Fructooligosaccharides (polymers of fructose) in some vegetables and wheat.
• A food and symptom diary is helpful to identify types and amounts of food that cause gastrointestinal symptoms. Restrict free fructose to less than 25 g at each meal or snack by limiting the amount of fruit or juice to one serving.
• Consume foods that contain fructose as part of a meal or snack to slow down digestion and absorption.
• Consume foods that contain both glucose and fructose or add foods that contain glucose when eating foods containing fructose to facilitate fructose absorption.
Lactose Intolerance: Deficiency of the enzyme lactase results in lactose overload in the intestinal tract. Symptoms are abdominal pain, bloating, gas, nausea and/or diarrhea. Diagnostic testing is usually not necessary as the cause if often clear and the remedy (lactase tablets, lactose reduced milk) is mostly effective. The most important thing about managing lactose intolerance is that it should not be an impediment to meeting your calcium requirements.
Gluten intolerance is a true food allergy and is discussed elsewhere.
Is Medical Nutrition Therapy (MNT) the Same for Hereditary vs Dietary Fructose Intolerance? Wendy Marcason. Journal of the American Dietetic Association. July 2010 (Vol. 110, Issue 7, Page 1128)