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What is fructose?
Name origin: from Latin fructus = fruit; -ose denotes sugar.
Nutrition Facts for Fructose:
- Calories per gram = 3.6 
- Glycemic index (GI) for a 25 g portion = 11 
- Sweetness, relative to sucrose = 120-190% [49,63]
- Net carbs = 100%
Fructose Chemical Formula
Fructose has the same chemical formula as glucose (C6H12O6), but with slightly different arrangement of atoms.
Picture 1. Fructose has a different structure than glucose.
Is fructose an essential nutrient?
Fructose is not an essential nutrient, which means you do not need to get it from food to be healthy. All fructose you need can be produced in your body from glucose.
- Fructose is a source of energy; it can provide 3.6 Calories per gram, which is about the same as sucrose (table sugar) [1,2].
- Fructose enhances the absorption of water, sodium and potassium .
Main fructose sources include fruits, fruit juices, honey, soft drinks sweetened by high-fructose corn syrup (HFCS), and products sweetened by agave syrup or invert sugar. Certain medicinal and multivitamin syrups are sweetened by fructose.
Table sugar (sucrose) is digested to glucose and fructose.
Fructose is called fruit sugar, because fruits are its main source, but fruits also contain other sugars, mainly glucose and sucrose.
Like most other nutrients, fructose is absorbed in the small intestine.
Healthy adults can absorb from 25 to about 50 grams of fructose from a fructose solution in one sitting [10,12].
Fructose is absorbed in the jejunum (the middle part of the small intestine) by the help of transport molecules GLUT5  and, in the presence of glucose (so, when consumed along with carbohydrates that can yield glucose) also by the GLUT2 transporters . Fructose can be also absorbed in the ileum (the last part of the small intestine) and colon by the help of GLUT7 transporters .
STIMULATORS of fructose absorption:
When the amount of glucose in a meal equals or exceeds the amount of fructose, than even in individuals with fructose malabsorption, all fructose from a meal should be absorbed [10,12,13,14,16,17,18].
In one experiment, only two of ten healthy adult participants completely absorbed 50 grams of fructose from a single meal, but all of them completely absorbed a combination of 50 grams of fructose and 50 grams of glucose, and also 100 grams of sucrose, which is made of 50% glucose and 50% fructose .
Fructose can be independently absorbed by the help of the transport molecule in the small intestinal lining, called GLUT-5; this transport is saturable – only up to about 50 grams of fructose from one meal can be absorbed this way. In the presence of glucose, fructose can be also absorbed by the help of the transport molecule GLUT-2; this transport is not saturable within realistic fructose intake [10,11].
Other enhancers of fructose absorption:
- Sucrose (table sugar)  and galactose (from milk) 
- Amino acids L-alanine, L-glutamine, L-phenylalanine and L-proline from meat and other protein foods 
- In diabetes 2, the absorption of fructose (and glucose and galactose) is enhanced due to an increased number of GLUT-2 and GLUT-5 transporters in the small intestinal lining [19,20].
INHIBITORS of fructose absorption:
- Sorbitol 
- Stress [10,19]
- Small intestinal bacterial overgrowth (SIBO) 
- Crohn’s disease 
- Celiac disease 
- Chemotherapy or radiation therapy
Fructose malabsorption is defined as an inability to completely absorb 25 grams or more of fructose from a test meal during a breath test with fructose [8,12,50]. Individuals with severe fructose malabsorption may not be able to absorb as little as 5 grams of fructose. Some researchers do not consider fructose malabsorption a disease but a physiological phenomenon .
A cause of fructose malabsorption is not known. The disorder can be present in infants or it can develop at any later time in life . Fructose malabsorption can also develop as a transitional complication in small intestinal bacterial overgrowth (SIBO) , celiac disease or Crohn’s disease .
Symptoms of fructose malabsorption can include excessive abdominal bloating and gas (flatulence), abdominal cramps and pain, diarrhea, constipation, nausea, vomiting, excessive belching, heartburn (gastric reflux) and lethargy or depression within few to several hours of ingesting fructose [8,27]. Constant diarrhea may result in an unintended weight loss.
Fructose malabsorption can be diagnosed on the basis of a positive hydrogen breath test with fructose, which can be ordered by a gastroenterologist or a registered dietitian. The test involves overnight fasting and then drinking a fructose solution, which usually contains 25 g of fructose, followed by measuring the amount of hydrogen in the exhaled air few hours later .
The test may be false negative in up to 30% of individuals with fructose malabsorption who do not expel hydrogen through the lungs .
Some individuals diagnosed with irritable bowel syndrome (IBS) may actually have fructose malabsorption and some can have both conditions.
Individuals with fructose malabsorption have a deficiency of a transport molecule called GLUT-5 in the small intestinal lining . After a meal, the fructose that remains unabsorbed stays in the intestine, attracts water from the body into the intestine and can thus trigger diarrhea. When fructose reaches the large intestine, normal intestinal bacteria consume it and convert it to gases, such as hydrogen, carbon dioxide and methane, which can cause abdominal bloating and excessive gas.
Fructose malabsorption has been also associated with depression; possible causes include tryptophan and folate deficiency [28,29,30,31]. The prevalence of fructose malabsorption among individuals with IBS is not higher than in general population .
Individuals with fructose malabsorption benefit from a low-fructose diet, which means avoiding meals that contain more than 0.5 g of “net fructose” (Chart 1), which is the amount of fructose higher than the total amount of glucose from all glucose sources in a meal: glucose (100% glucose), starch (100% glucose), maltose (100 % glucose), sucrose (50% glucose) and lactose (50% glucose) [7,8]. For example, a meal that contains 20 g fructose, 10 g starch (which is 10 g glucose) and 10 g sucrose (which is 5 g fructose and 5 g glucose) contains 20 g + 5 g fructose – (10 g + 5 g glucose) = 25 – 15 = 10 grams of net fructose.
Picture 1. Foods high in net fructose
Chart 1. Foods With Net Fructose
|FOOD (serving)||FRUCTOSE (g)||NET FRUCTOSE* (g)|
|Agave, cooked (100 g)||18.5||16|
|Pure fructose syrup (1 tbsp, 20 g)||13-16||Up to 16|
|Pear juice (1 cup, 237 mL)||18||14|
|Apple juice (1 cup, 237 mL)||16||8|
|Agave nectar (1 tbsp, 20 g)||11||7|
|Apple (1 medium, 180 g)||12.5||6.5|
|Pear (1 medium, 180 g)||12||6|
|Applesauce (1/2 cup, 122 g)||7||4.5|
|Mango (1 cup, sliced, 165 g)||7.5||4.5|
|Honey (1 tbsp, 21 g) ||6-9||Up to 4.5|
|Cola-type soft drink with HFCS-55 (1 cup, 237 mL)||15||4|
|Asian pear (4 oz, 110 g)||7||4|
|Watermelon (1 cup, diced, 150 g)||6||2.5|
|Sport drink (1 cup, 237 mL)||8||2.5|
|High fructose corn syrup (HFCS-55, isoglucose, fructose-glucose syrup) (1 tbsp, 20 g)||8.5||2|
|Carambola (star fruit) (3 oz, 85 g)||3||2|
|Mandarin (1 large, 6 oz, 170 g)||3.5||2|
|Feijoa (1 cup, 243 g)||7||1.5|
|Nance (1 cup, 120 g)||5.5||1.5|
|Guava, ripe (1 cup, 165 g)||3||1.5|
|Bread, white, reduced calories (3.5 oz, 100 g)||2.5||1.5|
|Grapes (1 cup, 150 g)||12.5||1.5|
|Grape juice (1 cup, 237 mL)||19||1.5|
|Raisins (2 oz, 57 g)||17||1|
|Bread, whole wheat (3.5 oz, 100 g)||4.5||1|
|Tomato, red, ripe (1 cup, 150 g)||2||1|
|Corn, yellow, from cob (100 g)||1.5||1|
|Orange (1 medium, 5 oz, 140 g)||2.5||1|
|Tangerines (1 cup, 195 g)||4.7||0.5|
|Strawberries (1 cup, 150 g)||3.5||0.5|
|Banana, ripe (7″, 120 g)||3.5||0.5|
|Pineapple (1 cup, 165 g)||12||0.5|
|Orange juice (1 cup, 237 mL)||10.5||0.5|
|Honeydew melon (1 cup, 177 g)||5||0.5|
|Cantaloupe (1 cup, 177 g)||3.5||0.5|
|Raspberries (1 cup, 120 g)||3||0.5|
|Cabbage, green (100 g)||2||0.5|
|Bagel (3.5 oz, 100 g)||1.5||0.5|
|Beans, green, microwaved (1/2 cup, 62 g)||1||0.5|
Chart 1 references: [5,6,7]
Other foods high in fructose but NOT in net fructose :
The following foods, which are high in fructose but not in net fructose, might also trigger symptoms in some individuals with fructose malabsorption:
- Sweeteners: invert sugar, blackstrap molasses
- Fruits: figs, jackfruit, lychee (litchis), pomegranate, sapote, banana, kiwifruit, dates, strawberries, currants (red and white)
Some individuals may also benefit from avoiding:
- Sorbitol and other sugar alcohols or polyols, such as xylitol, maltitol and mannitol in plums, prunes, chewing gum, candies and certain soft drinks
- Fructans (inulin and fructooligosaccharides or FOS) in wheat, onions, asparagus, Jerusalem artichokes, leeks and chicory roots
- Galactans in legumes (beans, peas, lentils)
- (Avoidance of all of the above nutrients is called a low-FODMAP diet)
Adding glucose to foods high in net fructose or consuming them along with starchy foods, for example eating an apple with bread, may prevent symptoms, but this may not work for everyone.
A low-fructose diet typically results in an obvious improvement of symptoms within 2-4 days, but it may take several weeks for all symptoms to disappear completely. If a low-fructose diet does not help, you can ask a doctor for additional tests, such as a breath test for lactose intolerance or small intestinal bacterial overgrowth (SIBO).
Chart 2. Low-Fructose Diet
|SAFE TO EAT||TO TRY||TO AVOID|
|SUGARS, SYRUPS, SWEETENERS|
|Acesulfam potassium, almond s., aspartame, barley malt s., brown rice s., brown sugar, Chinese rock sugar, chocolate s., corn s. (glucose s.), coconut s., corn syrup solids, dextrin, fondant, glucose (dextrose), glycerine (glycerol), glycogen, golden s. (cane s., light treacle), grape s., HFCS-42, high maltose corn syrup (HMCS), invert sugar (treacle), liquid glucose, maltodextrin (modified starch), maltose s., maple s., neotame, pancake s., raw sugar (Turbinado, Demerara, jaggery, coconut palm sugar – gur), rice s., saccharin, sorghum s., starch s., stevia, sucanat, sucralose, sucrose (table, beet or cane sugar), sucrose s. (liquid sugar), sukrin, tagatose, trehalose, trimoline *s. = syrup||Blackstrap molasses (black treacle), caramel, liquorice (licorice), dulcitol, (galactitol), erythritol, hydrogenated starch hydrolysates (HSH), isomalt, lactitol, maltitol, mannitol, xylitol||Agave nectar (in tequila, margaritas, soft drinks), fructose, high fructose corn syrup (HFCS-55), honey; rice fructose syrup (in China), sorbitol|
|SWEETS and DESERTS|
|Bonbons, cakes, candies, chocolate, confectionery, fudge, gelatin, gums, jellies, lollipops, marzipan, marshmallow, pies, puddings, sherbets (sorbets) and toffees containing “safe” sweeteners||Anything containing the above sweeteners||Anything containing the above “to avoid” sweeteners|
|Avocado, aubergine, cranberries, dates, figs, grapefruit, jack-fruit, kiwifruit, kumquat, lemons, limes, olives, passion fruit, persimmon, pomegranate||Apricot, banana, blackberries, blueberries, boysenberries, cantaloupe, cherries, currants, gooseberries, grapes, honeydew melon, lychee (litchis), mamey apple, nectarines, orange, papaya (pawpaw), peach, pineapple, plums, prunes, quince, raisins, rhubarb, strawberries, raspberries, tamarillo, tangelo||Apple, carambola (star fruit), custard apple, guava, mandarins (tangerines), mango, nashi fruit (Asian pear), pear, sultana, watermelon, zante currants and related juices, compotes and jams|
|Beets, bouillon, Brussel’s sprouts, carrots, cauliflower, celery, cucumber, dandelion greens, eggplant, endive, escarole, fennel, kale, lettuce, mustard greens, okra, potatoes (white, sweet), pumpkin, radishes, rutabagas, sauerkraut, shallots, spinach, swede, Swiss chard, turnip, watercress||Artichoke, asparagus, broccoli, cabbage, cucumbers (pickled), garlic, legumes (beans, peas and lentils), leeks, mushrooms, onions, peppers, squash (summer), tomatoes, zucchini|
|Barley, breads, pasta and ready-to-eat cereals without fructose, corn meal (degermed), cornflakes (non-flavored), grits, grouts, oatmeal, porridge (cooked oatmeal), plain muffins, rice (white, brown), rice or buckwheat noodles, rye bread, tortilla||Wheat, including dinkle, kamut, sourdoughs, spelt, wholemeal, and wheat products: biscuits, cookies, noodles, pasta, pastries; raisin bran|
|Meat, fish, other seafood, eggs, nuts, seeds||Coconut milk and cream|
|Plain, unsweetened milk, yogurt, cheese, custard, ice cream|
|SAUCES and SPICES|
|Basil, bay, cinnamon, cumin, curry, marjoram, oregano, parsley, rosemary, thyme, vinegar (apple cider, balsamic, distilled)||BBQ sauce, coriander, chutney, hot mustard, ketchup, parsnip, relish, soy sauce||Sauces: sweet & sour; Spices: chervil, dill weed, ginger, hot chili pepper|
|Water (tap, non-flavored bottled, mineral), tea, coffee, soft drinks sweetened by glucose, sucrose or other sweeteners listed above; dry wines, unsweetened distilled alcoholic beverages (gin, rum, vodka, whiskey)||Juices from fruits listed above; coffee substitutes with chicory; alcohol (fortified wines and liquers may be problematic)||Juices from fruits listed above, soft drinks with sorbitol or HFCS|
Chart 2 sources: USDA.gov , Tandofline , Foodintolerances.org 
Complications of Fructose Malabsorption
- Small intestinal bacterial overgrowth (SIBO)
- Fructose malabsorption may cause deficiency of tryptophan [27,28], folate [27,30] and zinc .
Hereditary Fructose Intolerance (HFI)
Hereditary fructose intolerance is a rare genetic disorder with the accumulation of fructose in the liver because of the lack of the enzyme fructose 1-phosphate aldolase, because of which fructose cannot be converted to glucose. Symptoms, such as severe abdominal cramps and vomiting, appear for the first time in early childhood after introduction of the fructose-containing foods .
Diet for HFI
Individuals with HFI should avoid foods containing even tiny amounts of fructose, sucrose, sorbitol, isomalt, maltitol, inulin, fructooligosaccharides (FOS), stachyose, raffinose, invert sugar, high fructose corn syrup (HFCS), agave nectar, blackstrap molasses and certain other syrups, which means most fruits and fruit products, certain vegetables, nuts, wheat products and commercial foods sweetened by mentioned sweeteners . Individuals with HFI should consult with their doctors or registered dietitians to get exact lists of foods to avoid. Here are extensive, but not complete lists of foods containing fructose and sucrose.
Other disorders of fructose metabolism: essential fructosuria and 3-fructose 1,6 bisphosphatase deficiency .
Essential fructosuria is a benign genetic disorder without symptoms in which fructose cannot be completely converted to glucose. The excessive amount of fructose is excreted in the urine [34,69].
Fructose Metabolism: the Fate of Fructose After Absorption
Most of the absorbed fructose enters the liver, where it is mainly converted to glucose: about 50% of the ingested fructose appears as blood glucose, which can be used as a source of energy; the rest of glucose is mainly stored as glycogen or converted to lactate . To a much smaller extent, fructose is converted to free fatty acids, ketone bodies, VLDL cholesterol and triglycerides .
The Effect of Fructose on the Insulin Release
Unlike glucose, fructose does not require insulin to be able to enter the body cells. Ingestion of fructose triggers only minor raise of insulin levels in healthy individuals, but markedly greater raise in individuals with diabetes .
The Effect of Fructose on Blood Glucose Levels
Fructose has a low glycemic index (GI = 11) and has a lower effect on the increase of blood glucose and insulin levels than other common carbohydrates [15-p.9;23,58,59,60]. Fructose ingested along with glucose, and sucrose, which is composed of 50% glucose and 50% fructose, raise insulin levels more than fructose or glucose alone .
The Effect of Fructose on LDL Cholesterol and Triglyceride Levels
Consumption of more than 50 grams of fructose per day may increase triglyceride levels after meals, and consumption of more than 100 g of fructose per day may increase fasting triglyceride and LDL cholesterol levels [23,67,76].
Fructose intake in excess of body calorie needs but not high fructose intake by itself may contribute to the development of metabolic syndrome (visceral obesity, high blood pressure, insulin resistance, high LDL cholesterol) [74,75].
Fructose and Exercise
- Moderate amounts of fructose may reduce the feeling of fatigue during exercise .
- Fructose added to other carbohydrates promotes carbohydrate oxidation during endurance training [23,45,46]. Ingested glucose can be oxidized at the maximum level 1.0-1.1 g/min, but a combination of glucose and fructose can result in up to 40% greater oxidation rate .
Possible Consequences of Excessive Fructose Intake
Currently, there is no evidence that free fructose–as in invert sugar or high-fructose corn sugar–would have more adverse effects than fructose as part of sucrose (which is 50% glucose, 50% fructose) .
The laxation threshold for fructose–the amount that can trigger diarrhea–is about 70 grams per day, but it may be significantly higher or lower in some individuals [15;p.237].
High fructose intake may increase blood uric acid levels (hyperuricemia) [23,77]. Hyperuricemia can increase the risk of gout.
In two studies, high fructose intake was modestly associated with an increased risk of gout in women  and strongly associated with increased risk of gout in men  but in one 2009 review it was not .
In one 2008 review of studies, high fructose intake was associated with increased risk of kidney stones .
Fructose can promote tooth decay, but less than sucrose and glucose [35,43].
Appetite and Weight Gain
- Fructose consumed as part of a mixed meal does not seem to have any effect on appetite .
- There seem to be no long-term differences in effects of fructose and glucose on weight gain [23,44,70].
According to 3 systematic reviews of studies, high fructose intake is not associated with high blood pressure [47,48,52].
Coronary Heart Disease
Currently, there is no firm evidence about the relation between high fructose consumption and coronary heart disease .
There is insufficient evidence about the association between high fructose intake and an increased risk of fatty liver [72,73].
Fructose and Diabetes Mellitus
Studies made so far have found no consistent relationship between high fructose intake, insulin resistance and diabetes 2 .
Fructose increases blood glucose levels after meals in individuals with diabetes 2 less than glucose or sucrose [60,61].
According to one 2012 systematic review of controlled feeding trials, replacing fructose for other carbohydrates have resulted in a decrease of HbA1c by 0.53%, in average .
Consumption of more than 60 g of fructose per day may increase triglyceride levels in individuals with diabetes 2 2 .
Oral fructose appears to be less effective in treating hypoglycemia than oral sucrose or glucose in children with diabetes 1 .
Fructose as a sweetener is usually produced from corn starch or sucrose, which is obtained from sugar cane or sugar beets.
Fructose and Cooking
- Commercially, fructose is available as a powder (fructose, crystalline fructose, fruit sugar) or syrup (pure fructose syrup).
- Fructose powder is as a white, crystalline substance, without odor, 120-190% as sweet as sucrose [17,64-p.275;68].
- Fructose is hygroscopic – it readily absorbs moisture from the air at relative humidity above 60° C [64-p.273;68].
- Fructose solubility in water at 77 °F (25 °C) is about 400 g/100 mL . Fructose solubility in 95% ethanol at 20° C is about 6 g/100 mL [64-p.274].
- Fructose melting point = 216-270 °F (102-132 °C); the melting point rises with the rate of heating .
- Fructose decomposes at 216-221 °F (102-105 °C) [64-p.273].
- Fructose is a reducing sugar  and it easily undergoes the Maillard browning reaction in the presence of amino acids .
- Caramelization of fructose starts at 230 °F (110 °C) .
- Hydrogenated starch hydrolysates (HSH)
- Fructo-oligosaccharides (FOS)
- Galacto-oligosaccharides (GOS)
- Human milk oligosaccharides (HMO)
- Isomalto-oligosaccharides (IMO)
- Mannan oligosaccharides (MOS)
- Raffinose, stachyose, verbascose
- SOLUBLE FIBER:
- Acacia (arabic) gum
- Beta mannan
- Carageenan gum
- Carob or locust bean gum
- Fenugreek gum
- Gellan gum
- Glucomannan or konjac gum
- Guar gum
- Karaya gum
- Psyllium husk mucilage
- Resistant starches
- Tara gum
- Tragacanth gum
- Xanthan gum
- INSOLUBLE FIBER:
- Chitin and chitosan
- Aspartic acid
- Glutamic acid
- FATTY ACIDS
- Alpha-linolenic acid (ALA)
- Eicosapentaenoic (EPA) and Docosahexaenoic acid (DHA)
- Arachidonic acid (AA)
- Linoleic acid
- Conjugated linoleic acid (CLA)
- Short-chain fatty acids (SCFAs)
- Medium-chain fatty acids (MCFAs)
- Long-chain fatty acids (LCFAs)
- Very long-chain fatty acids (VLCFAs)
- Vitamin A - Retinol and retinal
- Vitamin B1 - Thiamine
- Vitamin B2 - Riboflavin
- Vitamin B3 - Niacin
- Vitamin B5 - Pantothenic acid
- Vitamin B6 - Pyridoxine
- Vitamin B7 - Biotin
- Vitamin B9 - Folic acid
- Vitamin B12 - Cobalamin
- Vitamin C - Ascorbic acid
- Vitamin D - Ergocalciferol and cholecalciferol
- Vitamin E - Tocopherol
- Vitamin K - Phylloquinone
- Flavanols: Proanthocyanidins
- Flavanones: Hesperidin
- Flavonols: Quercetin
- Flavones: Diosmin, Luteolin
- Isoflavones: daidzein, genistein
- Caffeic acid
- Chlorogenic acid
- Tannic acid
- Alcohol chemical and physical properties
- Alcoholic beverages types (beer, wine, spirits)
- Denatured alcohol
- Alcohol absorption, metabolism, elimination
- Alcohol and body temperature
- Alcohol and the skin
- Alcohol, appetite and digestion
- Neurological effects of alcohol
- Alcohol, hormones and neurotransmitters
- Alcohol and pain
- Alcohol, blood pressure, heart disease and stroke
- Women, pregnancy, children and alcohol
- Alcohol tolerance
- Alcohol, blood glucose and diabetes
- Alcohol intolerance, allergy and headache
- Alcohol and psychological disorders
- Alcohol and vitamin, mineral and protein deficiency
- Alcohol-drug interactions
- Moderate, heavy, binge drinking
- Alcohol intoxication
- Alcohol poisoning
- Alcohol and gastrointestinal tract
- Alcoholic liver disease
- Long-term effects of excessive alcohol drinking
- Alcohol craving and alcoholism
- Alcohol withdrawal