Fructose intolerance is a condition where the body has difficult digesting and using fructose and fructose-containing foods. It is treated by complete elimination of fructose and sucrose from the diet.
There are two types of fructose intolerances. The first, hereditary fructose intolerance (HFI), also known as fructosemia or fructose aldolase B-deficiency, is a rare genetic disease of the metabolism of fructose due to the absence of the enzyme that breaks it down (aldolase B). As a result, fructose accumulates in the liver, kidney, and small intestine and the body is unable to convert its energy storage material (glycogen) into glucose. If untreated, the blood sugar level falls (hypogly-cemia) and there is formation of harmful substances that damage the liver. HFI is difficult to diagnose so its incidence rate is not known, but it is believed to be quite rare (between 1 in 12,000 to 1 in 58,000). Since it is inherited, it lasts for life.
The second type of fructose intolerance is dietary fructose intolerance (DFI), also called fructose mal-absorption. DFI is quite common, affecting up to 30% of people in the United States. Its incidence is also difficult to evaluate since many people show no symptoms at all and its cause is not precisely known. It
Sugars and sweeteners
|Barley malt syrup||Baker’s sugar|
|Birch sugar (if pure)||Beet sugar|
|Corn starch||Brown rice syrup|
|Corn sugar||Brown sugar|
|Erythitol (if pure)||Carob powder|
|Glucose polymers||Date sugar|
|Saccharin||Fruit juice sweeteners|
This list of sugars and sweeteners for fruitose intolerant individuals was prepared by the HFI Laboratory at Boston University .
(Illustration by GGS Information Services/Thomson Gale.)
seems to be caused by the lack of special cells (epithelial cells) on the surface of the intestine that are not available to help digestion. As a result, the body is not able to absorb fructose efficiently.
Although having different causes, both HFI and DFI are treated by dietary adjustments. Complete elimination of fructose and sucrose from the diet is the only effective treatment for HFI. As for DFI, treatment also involves a fructose-free diet, with the treating physician allowing some concessions in mild cases. Some patients may find a threshold level where they can eat some fructose without getting symptoms. Close dietary monitoring is important for good outcome and should include at least semiannual visits to a biochemical geneticist (for HFI) and monthly meetings with a nutritionist.
A strict fructose-free diet involves exclusion of any beverage or food containing fructose, sucrose, or sorbitol. Fructose is a monosaccharide, or simple sugar, that has the same chemical formula as glucose, the main source of energy for the body, but a different molecular structure. It is found in all fruits, in some vegetables and in honey. Fructose and other sugars are carbohydrates , which are important sources of energy for the body. The main types of sugars found in beverages and foods are:.
- Lactose: Disaccharide containing glucose and galactose. It occurs naturally in milk
- Maltose: Disaccharide containing two glucoses. It is obtained from starch
- Dextrose: Other name for glucose, it is obtained from sugar cane, sugar beets and starches
- Corn syrup: Sugar that consists chiefly of single glucose molecules. It is produced from corn starch
- High fructose corn syrup (HFCS): A mixture of glucose and fructose sugars, also produced from corn starch The HFI Laboratory at Boston University has prepared a list of sugars and their tolerance for patients. Some of the most common food sweeteners listed include:
- Agave syrup: Commonly used in Texan-Mexican foods, tequila, margaritas, soft drinks. High in fructose and not tolerated
- Aspartame: FDA-approved sugar substitute sold as Equal, NutraSweet, NutraTase. Tolerated
- Baker’s sugar: Another name for sucrose, the finest of all granulated sugars. Not tolerated
- Barley malt syrup: Obtained from sprouted grains of barley, kiln dried and cooked with water. Tolerated
- Beet sugar: Sucrose. Not tolerated
- Birch sugar: A sugar alcohol, xylitol. Trade name: The Ultimate Sweetener. Tolerated if pure
- Brown rice syrup: Obtained from brown rice. Possibly contains sucrose. Not tolerated
- Brown sugar: Sucrose coated with molasses. Not tolerated
- Cane sugar: Sucrose, table sugar. Not tolerated
- Carob powder: Obtained from the carob tree, it is 75% sucrose, plus glucose and fructose. Not tolerated
- Corn starch: Derived from corn, consists of straight or branched chains of glucose. Tolerated
- Corn sugar: Obtained from corn starch, contains glucose and maltose. Tolerated
- Corn syrup: Also obtained from corn starch, but in making the syrup, it usually has either maltose or fructose or both added. Not tolerated
- Date sugar: Made from dried, pulverized dates and likely to contain sucrose. Not tolerated
- Dextrin: Glucose molecules linked together in chains that do not break down to pure glucose. Tolerated
- Dulcitol: Naturally occurring sugar alcohol. Not tolerated
- Erythitol: Sugar alcohol. Tolerated if pure
Acidosis— Excessive acidity of body fluids due to accumulation of acids.
Carbohydrate— Any of a group of substances that includes sugars, starches, celluloses, and gums and serves as a major calorie source in food.
Digestion— The process by which food is chemically converted into nutrients that can be absorbed and used by the body.
Disaccharide— Any of a class of sugars, including lactose and sucrose, that are composed of two monosaccharides.
Enzyme— A protein that accelerates the rate of specific chemical reactions.
FDA— The Food and Drug Administration is the United States Department of Health and Human Services agency responsible for ensuring the safety and effectiveness of all drugs, biologics, vaccines, and medical devices.
Fructose— Sugar found in fruits.
Galactose— A sugar contained in milk. Galactose makes up half of the sugar called lactose that is found in milk.
Glucose— A monosaccharide sugar occurring widely in most plant and animal tissue. In humans, it is the main source of energy for the body.
Glycogen— The storage form of glucose found in the liver and muscles.
Hypoglycemia— A deficiency of sugar in the blood caused by too much insulin or too little glucose.
Malabsorption— Poor absorption of nutrients by the small intestine, difficulty in the digestion of nutrients.
Monosaccharide— Any of several carbohydrates, such as glucose, fructose, galactose, that cannot be broken down to simpler sugars.
Nutrient— A source of nourishment, especially a nourishing ingredient in a food.
Sorbitol— Sugar alcohol food additive used as a sweetener in commercially prepared low sugar foods and gum.
Starch— A naturally abundant nutrient carbohydrate found in seeds, fruits, tubers, and roots.
- Fruit juice sweeteners: Derived from grapes, apples or pears, heated to reduce water, leaving a sweeter more concentrated juice. Not tolerated.
- Grape syrup: Pure fructose. Not tolerated.
- Glucose: Simple sugar. Tolerated.
- Glucose polymers: Chains of glucose. Tolerated.
- Gur: Consists of 35% sucrose, and 15% mixture of glucose plus fructose, made from palm dates or sugar cane juice. Used in Thai cooking. Not tolerated.
- Honey: Natural syrup containing about 35% glucose, 40% fructose, 25 % water. Not tolerated.
- Maple syrup: From maple trees, mostly sucrose. Not tolerated
- Molasses: By-product of sugar cane with 24% water. Fructose level varies. Not tolerated
- Neotame: Sugar substitute. Tolerated.
- Polydextrose: Food additive synthesized from dextrose, plus about 10% sorbitol and 1% citric acid. It is commonly used as a replacement for sugar, starch, and fat in commercial cakes, candies, dessert mixes, gelatins, frozen desserts, puddings, and salad dressings. Not tolerated
- Saccharin: FDA-approved sugar substitute. No longer commonly used. Known as Sweet N’ Low, Sugar Twin, Sucryl, Featherweight. More than 6 servings per day may increase bladder cancer risk and it is no longer approved for use in Canada. Tolerated
- Sorbitol: Sugar alcohol common in fruits, particularly skin of ripe berries, cherries and plums. Not tolerated
- Stevia: Natural sweetener from a South American plant. Not tolerated
- Turbinado: Another name for raw sugar. Not tolerated
- Wasanbon: Grown on an island in the area of Japan from a special variety of sugar cane. Not tolerated Foods not allowed in a fructose and sucrose-free diet include:
- Meats: Cold cuts, hot dogs, sausages, any meat products that contain sugar
- Cereals: Any cereal sweetened with sugar, fructose, or sorbitol
- Sweeteners: Sugar, sucrose, fructose, sorbitol, brown sugar, molasses, honey
- Fruits: All fruits, fruit juices, fruit extracts, dehydrated fruits, and products that contain fruit or are sweetened with fruit juice or concentrate
- Fats: Mayonnaise, mustards and dressings with sugar.
- Milk: Milk and dairy products with added sugar.
- Nuts: Candy-covered nuts or nuts prepared with sugar, fructose or sorbitol.
- Breads: Any type of sweet bread, or any that may contain sugar, fructose or sorbitol.
- Potatoes: Sweet potatoes.
- Fish: Processed fish with sugar.
- Desserts: Any dessert that contains sugar, fructose or sorbitol.
- Vegetables: Carrot, tomato, corn, canned vegetables with sugar.
- Other foods: Catsup, sauces that contain sugar, chile piquin with lemon, all regular soft drinks and sodas, jams, jellies, marmalades, maple syrup, canned or bottled fruits, corn syrup All types of fruits must be eliminated from fructose and sucrose-free diet. Examples of foods that are allowed include:
- Meats: Red meat, pork, chicken and turkey
- Cereals: Any that do not contain sugar, fructose or sorbitol.
- Sweeteners: Aspartame, dextrine, no-calorie sweeteners.
- Fats: Butter, margarine, oil, salad dressings without sugar.
- Eggs: Any type.
- Milk: Any type
- Nuts: Any type that has no sugar.
- Breads: Any type that does not contain sugar, fructose or sorbitol as ingredient.
- Potatoes: White potatoes.
- Pasta and soups: Macaroni, spaghetti, rice, soup pasta.
- Fish: Any fresh fish.
- Desserts: Natural yogurt, cakes and ice-cream made without sugar.
- Cheese: Any type.
- Vegetables: Asparagus, cauliflower, peppers, lettuce, spinach, celery, root vegetables except carrots.
- Other foods: Coffee, tea, diet soft drinks that contain artificial sweeteners, cocoa, salt, pepper and other spices Additional guidelines for a fructose-free diet include:
- Fructose, sucrose and sorbitol are used in many manufactured foods to such an extent that very few processed foods are allowed in the diet. Sugar is used in many other less obvious products such as canned food, bottled sauces
- Flavorings is another possible trace source of these sugars as they are sometimes used to carry flavoring compounds into foods
- Only vegetables that contain predominantly starch are allowed in the diet. Cooked vegetables have a lower fructose content and should be selected rather than raw vegetables as the cooking process results in a loss of free sugars
- New potatoes have a higher fructose content than old potatoes
- Wholemeal flour contains more fructose than white flour because both germ and bran contain sucrose. Other wholegrain foods (brown rice and wholemeal pasta) also contain more sucrose than the refined products
- Sorbitol is very often used as an artificial sweetener, especially in diabetic foods and drinks which should accordingly be avoided. Isomalt and lycasin, alternative sweeteners that are predominantly used in confectionary, also contain sorbitol. Glucose can be used as an alternative sweetener and as a source of energy
- Sucrose and sorbitol are also often used in medications as bulking agents or to improve the taste
The symptoms of both types of fructose intolerance are gastrointestinal distress, flatulence, bloating, diarrhea, fatigue, vomiting, low iron and other nutrient deficiency. For dietary fructose intolerance, there is clinical evidence also associating it with mood disturbances and depression. The function of a fructose-free diet is to eliminate dietary sugar intake so as to alleviate these symptoms.
Absolute elimination of fructose and glucose from the diet produces good outcomes in most people with fructose intolerance. For the rapidly diagnosed and treated infant, the outcome for a normal state of health is excellent. In the absence of substantial liver damage, life expectancy is normal.
Eating out is one of the most challenging parts of maintaining a fructose-free diet. This is because restaurant employees have little time to check food contents from the labels of the ingredients used by the kitchen to prepare menus. Some guidelines in dealing with restaurant staff include:.
- Be as clear and explicit as possible when talking with the waiting staff. Explain your fructose intolerance in brief terms and order only foods that you know cannot have sugars and how they should be prepared. For example, order a steak, broiled on a piece of aluminum foil with no seasonings at all, a baked potato with butter, a lettuce-only salad with a small slice of lemon and oil on the side, plain steamed spinach and coffee/tea/milk
- The person who knows the ingredients in the food is the person who prepares it. Ask to speak to that person. It can be the chef, or the cook, rarely the restaurant manager
- Be careful of soups. Except for upscale restaurants, most soups are canned. Ask to read the label. If the soup is made at the restaurant it may also contain ingredients not compatible with a fructose-free diet
- Whether grilled or broiled, seasoning is routinely used in meat preparation, so specify no seasonings in your order. The chef will know if a sauce has fructose-containing ingredients. Canned sauces are also used in many restaurants. Request to check the ingredient list
- Non-dairy products are often used in restaurants, and may contain untolerated ingredients. Three frequently used non-dairy products in restaurants are non-dairy creamer, non-dairy potato topping, and non-dairy whipped topping. Also ask to read their labels
With the increasing popularity of processed foods, sugar is often an ingredient about which the consumer is not aware, and not only in restaurants. For example, high fructose corn syrup (HFCS) is present and unsuspected in numerous products including soft drinks, fruit drinks, sports drinks, baked goods, candies, jams, yogurts, condiments, canned and packaged foods, and other prepared and sweetened foods. Also, potatoes, when prepared a certain way, may provide a significant amount of fructose. For this reason, the advice of a highly trained nutritionist is required in the treatment of fructose intolerance.
After ingesting fructose, infants and children may become sufficiently ill to require hospitalization. If untreated, fructose intolerance leads to hypoglycemia and acidosis that may act together to cause organ shock and coma. Ongoing liver damage may result in cirrhosis and eventual liver failure. Death may result from any or all of the above. Hereditary fructose intolerance may be relatively mild or a very severe disease. In the severe form, even eliminating fructose and sucrose from the diet may not prevent progressive liver disease.
QUESTIONS TO ASK YOUR DOCTOR
- What is the difference between dietary fructose intolerance and hereditary fructose intolerance?
- How common are dietary fructose intolerance and hereditary fructose intolerance?
- Do I have dietary fructose intolerance and hereditary fructose intolerance?
- How did I get it?
- What are the complications?
- Can I be cured?
- How is fructose intolerance identified?
- What are the symptoms of dietary fructose intolerance and hereditary fructose intolerance?
- How is fructose intolerance treated?
- Which foods and beverages contain fructose?
- Which foods and beverages contain high fructose corn syrup?
- Can I consume any fructose at all?
- Can I consume artificial sweeteners?
Clinical intolerance to fructose was initially described in 1956. Some 4-5 years later, the defect in aldolase B enzyme in the liver was demonstrated, and hereditary fructose intolerance (HFI) became clinically recognized. The rapid early progress in the understanding of this disorder may be due to the fairly clear symptoms associated with ingestion of fructose, which are difficult to miss. In many young infants, the age of onset of symptoms leads to the diagnosis. Genetic counseling may be of value to prospective parents with a family history of fructose intolerance. Medical experts agree that definitive treatment simply consists of eliminating fructose from the diet. By doing so early in the course, the affected child’s health is usually fully restored within days.
Recent research performed at the University of Innsbruck in Austria shows that fructose and sorbi-tol-reduced diet in subjects with fructose malabsorp-tion does not only reduce gastrointestinal symptoms but also improves mood and early signs of depression. Improvement of the signs of depression was also more pronounced in females than in males.
Medical researchers unanimously agree that symptoms can improve in dietary fructose intolerance patients willing to adhere to a low fructose diet.
Smith, J. Living With Dietary Fructose Intolerance: A Guide to Managing your Life With this New Diagnosis Charleston, SC: BookSurge Publishing, 2006.
Gazzola, A. Living with Food Intolerance London, UK: Sheldon Press, 2006.
Saville, A., Haynes, A. Food Intolerance Bible New York, NY: ThorsonsElement (Harpercollins), 2005.
Minocha, A. Handbook of Digestive Diseases Thorofare, NJ: Slack Incorporated, 2004.
Emsley, J., Fell, P. Was It Something You Ate?: Food Intolerance: What Causes It and How to Avoid It. Oxford, UK: Oxford University Press, 2002.
Frieri, M, Kettelhut, B. (eds). Food Hypersensitivity and Adverse Reactions Boca Raton, FL: S. CRC Press, 1999.
Cornblath, M., Schwartz, R. Disorders of Carbohydrate Metabolism in Infancy. Cambridge, MA: Blackwell Scientific Publications, 1991.
National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK), National Institutes of Health. 31 Center Drive, MSC 2560, Bethesda, MD 20892-2560. 1-800-891-5389. <digestive.niddk.nih.gov/ddiseases/pubs/facts/index.htm>.
American Gastroenterological Association. 930 Del Ray Avenue, Bethesda, MD 20814. (301)654-2055. <www.gastro.org>.
International Foundation for Functional Gastrointestinal Disorders Inc. P.O. Box 170864, Milwaukee, WI 53217-8076. 1-888-964-2001. <www.iffgd.org>.
Genetic and Rare Diseases (GARD) Information Center, PO Box 8126, Gaithersburg, MD 20898-8126. 1-301-519-3194.<http://rarediseases.info.nih.gov/html/resources/info_cntr.html>
Monique Laberge, Ph.D.