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Ask a Dietitian

"Diana, just a quick heads up to let you know we are still using your cookbook and the guys will often be heard saying what would Diana say about this or that....really good feed back... I made your potato salad and the oriental coleslaw on Sat. for a family luncheon and had rave reviews so thanks again."

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Sugar Intolerance

January 7th, 2007


Gastrointestinal discomfort can result from a number of issues including types foods ingested, volume of food, functional issues and speed at which food goes through the intestinal tract. Sugar intolerance and malabsorption has been found to be an issue for some individuals causing gastrointestinal distress, flatulence, bloating, diarrhea, fatigue and anemia. There are many different types of sugars and it is important to pin point which one is the culprit if you suspect intolerance or malabsorption.

Types of sugars
The different types of sugars found in the diet are found in single form as galactose, glucose and fructose which in different combinations form disaccharides called: sucrose, lactose and maltose. Glucose is usually present as starch and cellulose and is responsible for maintaining our “blood sugar” which the brain highly depends on. Fructose is also known as fruit sugar and is the sweetest of the sugars. Galactose is mostly found in milk products.

Intolerance versus Malabsorption

Sugar Malabsorption (not to be confused with intolerance) is the inability in some people to break down sugars in the small intestine. It results in sugars being broken down into gases by bacteria in the large intestine, causing bloating, pain, diarrhea and flatulence. The inability to absorb sugars properly can lead to other nutrients being malabsorbed such as calcium and iron. Some studies have even associated fructose malabsorption with early stages of depression and mood disorders. It has also been found to be a trigger for Irritable Bowel Syndrome (IBS) symptoms (such as bloating, diarrhea, constipation, pain, gas).

Fructose Malabsorption: Malabsorption of fructose is caused by the inability of the small intestine to absorb fructose appropriately due to a deficiency of the fructose carrier in the enterocytes. This causes the fructose to end up in the large intestine which can create bloating, flatulence and diarrhea. No known cure but an appropriate fructose lowered diet can help (see below for a list of foods high in fructose). Depending on how sensitive the individual is to high fructose foods, they can be eaten in moderation. Lastly, foods with glucose actually help individuals absorb fructose better.

Foods with high fructose content: Apples, coconut milk, figs, fruit juice, guavas, high fructose corn syrup (found in soft drinks and sushi rice), honey, lychees, mangos, melons, pawpaws, pears, persimmons, prunes, raisins.
Foods with high fructan (chains of fructose) content: Artichokes, asparagus, green beans, leeks, onions. For some, limiting wheat products can help. Therefore, including grains such as rice, rye, spelt, quinoa, barley and amaranth is important. While individuals do not need to avoid gluten, products labeled “gluten free” are appropriate unless they contain fructose or dried fruit (eg. Gluten free raisin bread).Note: There is less evidence that fructans can be as problematic for individuals with fructose malabsorption.

Sugar Intolerance is a hereditary condition in which the liver enzymes that break down fructose are deficient. It is rarer than sugar malabsorption and is usually diagnosed at birth.

Fructose Intolerance: Symptoms include severe abdominal pain, vomiting and hypoglycemia. If fructose ingestion continues it can lead to hepatic and/or renal failure and death. Clinical symptoms include severe abdominal pain, vomiting and hypoglycemia after ingestion of fructose or other sugars.
Tests for Sugar Intolerance: Enzyme tests and liver function tests are the main tests to confirm diagnosis. Genetic testing for fructose intolerance may also be available.
Treatment: Complete elimination of fructose and sucrose from the diet is the most effective treatment for patients. Prognosis depends on how soon the diagnosis is made.

Disaccharide Intolerance I: Rare inherited metabolic disorder characterized by sucrase and isomaltase enzyme deficiency, which are fundamental in the breakdown of certain sugars (ie. Sucrose) and products of starch digestion (dextrins). Symptoms usually surface soon after infants are fed modified milk formulas with sucrose or polycose, and include watery diarrhea, abdominal swelling and/or discomfort. Breastfed infants or those using lactose-only formula do not show symptoms (until sucrose is introduced through juice etc.). Intolerance to starch and the symptoms of sucrose intolerance can decrease with age.

Glucose-Galactose Intolerance: This disorder has only been found in about 8 cases with symptoms identical to disaccharide intolerance. The only tolerated carbohydrate is fructose and therefore would be advisable to consult a dietitian to assess balanced food choices.

Trehalose Intolerance: This disorder is thought to be an autosomal recessive trait that occurs due to a deficiency of the trehalase enzyme. It has been reported in Greenland at a frequency of 8%. Trehalose can be found in mushrooms, which must be eliminated if intolerance is diagnosed. It is not a usual disaccharide (sugar) and therefore has not shown any nutritional consequence until recently when it has been introduced as a sweetener in foods.

Lactose Intolerance: Probably one of the more well known intolerances. It results from the inability of individuals to digest significant amounts of lactose (a sugar found in milk products) due to the deficiency of the enzyme lactase. Symptoms can range from mild to severe, including nausea, cramping, bloating, gas and diarrhea. The most common tests to diagnose lactose intolerance are: lactose tolerance, hydrogen breath and stool acidity tests. Some people may think they have lactose intolerance as the symptoms can be confused with other disorders such as irritable bowel syndrome.
Treatment: Decreasing lactose in the diet is a primary treatment method, while others who are very sensitive to lactose in their food can also buy lactase pills or drops to add to foods. It is important to drink other sources of calcium rich foods if one is eliminating milk and milk products. Look for fortified juices, soy/rice/almond milk in your grocer or buy lactaid milk.

Bottom-line: It is important to find out the root cause of your indigestion or gastrointestinal discomfort before eliminating foods. When a diagnosis is made consult a dietitian if there are restrictions to your diet that may decrease your nutrient intake.