Fructose and its malabsorption
May 8, 2013 19:11:41 GMT
Post by Charlie Arnold on May 8, 2013 19:11:41 GMT
This section is for general information therefore can be read by anyone but not added to. If anyone feels anything should be added or amended please PM me and I will make the alterations. That way this general information is accessible to all for starting to find out more about the condition and saves repetition and getting lost over time.
This information is taken from the wikipedia page on fructose:
What is fructose?
Fructose, or fruit sugar, is a simple monosaccharide found in many plants, which is also similar to sucrose. It is one of the three dietary monosaccharides, along with glucose and galactose, that are absorbed directly into the bloodstream during digestion. Fructose was discovered by French chemist Augustin-Pierre Dubrunfaut in 1847. Pure, dry fructose is a very sweet, white, odorless, crystalline solid and is the most water-soluble of all the sugars. From plant sources, fructose is found in honey, tree and vine fruits, flowers, berries, and most root vegetables. In plants, fructose may be present as the monosaccharide or as a molecular component of sucrose, which is a disaccharide.
Commercially, fructose frequently is derived from sugar cane, sugar beets, and corn and there are three commercially important forms. Crystalline fructose is the monosaccharide, dried, ground, and of high purity. The second form, high-fructose corn syrup (HFCS) is a mixture of glucose and fructose as monosaccharides. The third form, sucrose, is a compound with one molecule of glucose covalently linked to one molecule of fructose. All forms of fructose, including fruits and juices, are commonly added to foods and drinks for palatability and taste enhancement, and for browning of some foods, such as baked goods.
Natural sources of fructose include fruits, vegetables (including sugar cane), and honey. Fructose is often further concentrated from these sources. The highest dietary sources of fructose, besides pure crystalline fructose, are foods containing table sugar (sucrose), high-fructose corn syrup, agave nectar, honey, molasses, maple syrup, and fruit juices, as these have the highest percentages of fructose (including fructose in sucrose) per serving compared to other common foods and ingredients. Fructose exists in foods either as a free monosaccharide or bound to glucose as sucrose, a disaccharide. Fructose, glucose, and sucrose may all be present in a food; however, different foods will have varying levels of each of these three sugars.
Fructose is also found in the synthetically manufactured sweetener, high-fructose corn syrup (HFCS). Hydrolyzed corn starch is used as the raw material for production of HFCS. Through the enzymatic treatment, glucose molecules are converted into fructose. There are three types of HFCS, each with a different proportion of fructose: HFCS-42, HFCS-55, and HFCS-90. The number for each HFCS corresponds to the percentage of synthesized fructose present in the syrup. HFCS-90 has the highest concentration of fructose, and typically, is used to manufacture HFCS-55; HFCS-55 is used as sweetener in soft drinks, whereas HFCS-42 is used in many processed foods and baked goods.
How is fructose absorbed?
Fructose exists in foods either as a monosaccharide (free fructose) or as a unit of a disaccharide (sucrose). Free fructose is absorbed directly by the intestine. When fructose is consumed in the form of sucrose, it is digested (broken down) and then absorbed as free fructose. As sucrose comes into contact with the membrane of the small intestine, the enzyme sucrase catalyzes the cleavage of sucrose to yield one glucose unit and one fructose unit, which are then each absorbed. After absorption it enters the hepatic portal vein and is directed toward the liver.
The mechanism of fructose absorption in the small intestine is not completely understood. Some evidence suggests active transport, because fructose uptake has been shown to occur against a concentration gradient. However, the majority of research supports the claim that fructose absorption occurs on the mucosal membrane via facilitated transport involving GLUT5 transport proteins. Since the concentration of fructose is higher in the lumen, fructose is able to flow down a concentration gradient into the enterocytes, assisted by transport proteins. Fructose may be transported out of the enterocyte across the basolateral membrane by either GLUT2 or GLUT5, although the GLUT2 transporter has a greater capacity for transporting fructose, and, therefore, the majority of fructose is transported out of the enterocyte through GLUT2.
What is fructose malabsorption?
Fructose malabsorption, formerly named "dietary fructose intolerance," is a digestive disorder in which absorption of fructose is impaired by deficient fructose carriers in the small intestine's enterocytes. This results in an increased concentration of fructose in the entire intestine.
This condition is common in patients identified to be suffering symptoms of irritable bowel syndrome, although occurrence in these patients is not higher than occurrence in the normal population. Conversely, patients with fructose malabsorption often fit the profile of those with irritable bowel syndrome. A small proportion of patients with both fructose malabsorption and lactose intolerance also suffer from celiac disease.
Fructose is absorbed in the small intestine without help of digestive enzymes. Even in healthy persons, however, only about 25–50g of fructose per sitting can be properly absorbed. People with fructose malabsorption absorb less than 25g per sitting. In the large intestine, fructose that has not been adequately absorbed reduces the absorption of water osmotically and is metabolized by colonic bacteria into short chain fatty acids, producing the byproduct gases hydrogen, carbon dioxide and methane.[citation needed] This abnormal increase in hydrogen is detectable with the hydrogen breath test.
The physiological consequences of fructose malabsorption include increased osmotic load, rapid bacterial fermentation, altered gastrointestinal motility, the formation of mucosal biofilm and altered profile of bacteria. These effects are additive with other short-chain poorly absorbed carbohydrates such as sorbitol. The clinical significance of these events depends upon the response of the bowel to such changes; they have a higher chance of inducing symptoms in people with functional gut disorders than asymptomatic subjects. Some effects of fructose malabsorption are decreased tryptophan, folic acid and zinc in the blood.
Restricting dietary intake of free fructose and/or fructans may provide symptom relief in a high proportion of patients with functional gut disorders.
Symptoms
Bloating (from fermentation in the small and large intestine)
Diarrhea and/or constipation
Flatulence
Stomach pain (as a result of muscle spasms, the intensity of which can vary from mild and chronic to acute but erratic)
Vomiting (if great quantities are consumed)
Early signs of mental depression
Nausea
This information is taken from the wikipedia page on fructose:
What is fructose?
Fructose, or fruit sugar, is a simple monosaccharide found in many plants, which is also similar to sucrose. It is one of the three dietary monosaccharides, along with glucose and galactose, that are absorbed directly into the bloodstream during digestion. Fructose was discovered by French chemist Augustin-Pierre Dubrunfaut in 1847. Pure, dry fructose is a very sweet, white, odorless, crystalline solid and is the most water-soluble of all the sugars. From plant sources, fructose is found in honey, tree and vine fruits, flowers, berries, and most root vegetables. In plants, fructose may be present as the monosaccharide or as a molecular component of sucrose, which is a disaccharide.
Commercially, fructose frequently is derived from sugar cane, sugar beets, and corn and there are three commercially important forms. Crystalline fructose is the monosaccharide, dried, ground, and of high purity. The second form, high-fructose corn syrup (HFCS) is a mixture of glucose and fructose as monosaccharides. The third form, sucrose, is a compound with one molecule of glucose covalently linked to one molecule of fructose. All forms of fructose, including fruits and juices, are commonly added to foods and drinks for palatability and taste enhancement, and for browning of some foods, such as baked goods.
Natural sources of fructose include fruits, vegetables (including sugar cane), and honey. Fructose is often further concentrated from these sources. The highest dietary sources of fructose, besides pure crystalline fructose, are foods containing table sugar (sucrose), high-fructose corn syrup, agave nectar, honey, molasses, maple syrup, and fruit juices, as these have the highest percentages of fructose (including fructose in sucrose) per serving compared to other common foods and ingredients. Fructose exists in foods either as a free monosaccharide or bound to glucose as sucrose, a disaccharide. Fructose, glucose, and sucrose may all be present in a food; however, different foods will have varying levels of each of these three sugars.
Fructose is also found in the synthetically manufactured sweetener, high-fructose corn syrup (HFCS). Hydrolyzed corn starch is used as the raw material for production of HFCS. Through the enzymatic treatment, glucose molecules are converted into fructose. There are three types of HFCS, each with a different proportion of fructose: HFCS-42, HFCS-55, and HFCS-90. The number for each HFCS corresponds to the percentage of synthesized fructose present in the syrup. HFCS-90 has the highest concentration of fructose, and typically, is used to manufacture HFCS-55; HFCS-55 is used as sweetener in soft drinks, whereas HFCS-42 is used in many processed foods and baked goods.
How is fructose absorbed?
Fructose exists in foods either as a monosaccharide (free fructose) or as a unit of a disaccharide (sucrose). Free fructose is absorbed directly by the intestine. When fructose is consumed in the form of sucrose, it is digested (broken down) and then absorbed as free fructose. As sucrose comes into contact with the membrane of the small intestine, the enzyme sucrase catalyzes the cleavage of sucrose to yield one glucose unit and one fructose unit, which are then each absorbed. After absorption it enters the hepatic portal vein and is directed toward the liver.
The mechanism of fructose absorption in the small intestine is not completely understood. Some evidence suggests active transport, because fructose uptake has been shown to occur against a concentration gradient. However, the majority of research supports the claim that fructose absorption occurs on the mucosal membrane via facilitated transport involving GLUT5 transport proteins. Since the concentration of fructose is higher in the lumen, fructose is able to flow down a concentration gradient into the enterocytes, assisted by transport proteins. Fructose may be transported out of the enterocyte across the basolateral membrane by either GLUT2 or GLUT5, although the GLUT2 transporter has a greater capacity for transporting fructose, and, therefore, the majority of fructose is transported out of the enterocyte through GLUT2.
What is fructose malabsorption?
Fructose malabsorption, formerly named "dietary fructose intolerance," is a digestive disorder in which absorption of fructose is impaired by deficient fructose carriers in the small intestine's enterocytes. This results in an increased concentration of fructose in the entire intestine.
This condition is common in patients identified to be suffering symptoms of irritable bowel syndrome, although occurrence in these patients is not higher than occurrence in the normal population. Conversely, patients with fructose malabsorption often fit the profile of those with irritable bowel syndrome. A small proportion of patients with both fructose malabsorption and lactose intolerance also suffer from celiac disease.
Fructose is absorbed in the small intestine without help of digestive enzymes. Even in healthy persons, however, only about 25–50g of fructose per sitting can be properly absorbed. People with fructose malabsorption absorb less than 25g per sitting. In the large intestine, fructose that has not been adequately absorbed reduces the absorption of water osmotically and is metabolized by colonic bacteria into short chain fatty acids, producing the byproduct gases hydrogen, carbon dioxide and methane.[citation needed] This abnormal increase in hydrogen is detectable with the hydrogen breath test.
The physiological consequences of fructose malabsorption include increased osmotic load, rapid bacterial fermentation, altered gastrointestinal motility, the formation of mucosal biofilm and altered profile of bacteria. These effects are additive with other short-chain poorly absorbed carbohydrates such as sorbitol. The clinical significance of these events depends upon the response of the bowel to such changes; they have a higher chance of inducing symptoms in people with functional gut disorders than asymptomatic subjects. Some effects of fructose malabsorption are decreased tryptophan, folic acid and zinc in the blood.
Restricting dietary intake of free fructose and/or fructans may provide symptom relief in a high proportion of patients with functional gut disorders.
Symptoms
Bloating (from fermentation in the small and large intestine)
Diarrhea and/or constipation
Flatulence
Stomach pain (as a result of muscle spasms, the intensity of which can vary from mild and chronic to acute but erratic)
Vomiting (if great quantities are consumed)
Early signs of mental depression
Nausea