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DIETARY FACTORS THAT FACILITATE FRUCTOSE ABSORPTION In previous studies, glucose, galactose (6, 11, 12, 20), and certain amino acids (21) increased fructose absorption. The extent to which glucose increases fructose absorption depends on the proportion of glucose relative to fructose (6). An equimolar dose of glucose prevented incomplete fructose absorption in healthy subjects (6, 11) and glucose at one-half the fructose dose decreased the prevalence of incomplete absorption by over 50% (6). Glucose and certain amino acids (e.g., alanine, proline, and glutamine) (21) facilitated fructose absorption, presumably by solvent drag and passive diffusion (2023). In addition, it is conceivable that glucose delayed gastric emptying, thereby facilitating fructose absorption (24). SORBITOL IMPEDES FRUCTOSE ABSORPTION Sorbitol is one of several sugar alcohols found naturally (Table 1) and used as "sugar-free" sweeteners by food industry, primarily because they do not promote tooth decay or cause hyperglycemia. For these reasons, sugar alcohols are used in "sugarless" gums and candies, and in ketogenic and diabetic foods. Sorbitol is incompletely absorbed (25). Moreover, doses of sorbitol and fructose that are absorbed when ingested separately may be incompletely absorbed when taken together (26). Incomplete absorption of fructose and sorbitol may cause gastrointestinal symptoms in IBS. Thus, 4075% of healthy subjects (27, 28) incompletely absorbed a mixture of fructose (25 g) and sorbitol (5 g); most were asymptomatic (27) and breath hydrogen levels did not correlate with symptoms (27, 28). By comparison, 30100% of IBS patients (1518, 27, 28) incompletely absorbed this mixture. Moreover, in contrast to fructose alone (16), the prevalence of gastrointestinal symptoms after fructosesorbitol ingestion was higher in IBS patients compared to healthy subjects (16, 27, 28). This interaction between fructose and sorbitol absorption is critical to understanding the gastrointestinal effects of sweeteners since it is likely that these sweeteners will be consumed together as fruits/juices (Table 1) or as a result of combining processed foods. The interaction between fructose and sorbitol absorption may reflect competition for the same receptor (26) or acceleration of transit by a synergistic osmotic effect (29). The effects of glucose on absorption of a fructosesorbitol mixture are unknown. Since glucose enhanced the absorption of sorbitol (3032) and fructose administered separately (6, 11, 20), it is conceivable that glucose will also facilitate absorption of a fructosesorbitol mixture. EFFECT OF FRUCTOSE AND FRUCTOSESORBITOL RESTRICTED DIETS IN IBS Functional gastrointestinal symptoms resolved after dietary fructose restriction in an unblinded, uncontrolled report of four patients (33). Forty percent (16) to 56% (34) of IBS patients reported substantial improvement in symptoms after restriction of one or more of the following (i.e., lactose, fructose, sorbitol) incompletely absorbed sugar(s). Patient compliance with fructose-restricted diets has been variable (35, 36). Thus, only 54% of subjects instructed in a fructose-restricted diet complied with dietary fructose restriction for more than 50% of the time from 6 to 18 months after beginning the diet (36). Patient compliance is influenced, among other factors, by the widespread distribution of fructose in food products. Gastrointestinal symptoms improved significantly in patients who complied, but not in patients who did not comply with a fructose-restricted diet. DIETARY IMPLICATIONS These studies can be used to guide dietary recommendations for patients who may be fructose intolerant. Assuming that an equimolar amount of glucose prevents incomplete fructose absorption in functional bowel disease as it does in healthy subjects, then only sources containing more fructose than glucose, (i.e., excess fructose) need to be restricted. Fruits and juices that provide glucose in equal (or greater) amounts as fructose (i.e., bananas, strawberries) may be well tolerated. Fruits and juices containing excess fructose (i.e., honey, dates, oranges) or excess fructose plus sorbitol (i.e., cherries, apples, pears) may be poorly tolerated, particularly if ingested in excess and/or without other food or drink.The main source of fructose in processed foods is high-fructose corn syrups (HFCS). These are mixtures containing either approximately 42 or 55% fructose as defined in Title 21, Chapter I, Part 184, Sec. 184.1866 in the Code of Federal Regulations. In contrast to HFCS, corn syrup mainly contains glucose derivatives (3). Although the name suggests otherwise, glucose is the predominant sugar present in HFCS-42 (53% glucose, 42% fructose, 5% oligosaccharide) (1). HFCS-55 (42% glucose, 55% fructose, 3% oligosaccharide) contains a small excess of fructose (1). Foods sweetened with HFCS contain one of these two fractions. While fractions approaching pure fructose are available, their use is limited to specialty items such as nutritional bars and "lite" or reduced calorie snacks and beverages.Fructose absorption after ingestion of fructose alone has not been compared to absorption of fructose contained in HFCS. HFCS-42 contains glucose in excess of fructose and should be well absorbed. The small amount of excess fructose in HFCS-55 may be incompletely absorbed, particularly in individuals with a low absorptive capacity for fructose. Since ingredient labels do not specify which fraction they contain, a conservative approach is to treat all HFCS products as though they contain HFCS-55. A 12-ounce cola sweetened with HFCS-55 contains about 40 g of the sweetener, i.e., 22 grams of fructose and 17 grams of glucose, representing a fructose excess of 5 g per can. Only 1 of 10 healthy individuals incompletely absorbed 10 g (possibly even 5 g) of fructose and had no symptoms (6).Unless the absorptive capacity for fructose in functional bowel disease differs from healthy subjects, most people will absorb the excess fructose (i.e., fructose in excess of glucose) present in fruit, juice, or processed foods when ingested in recommended serving sizes. One approach to the patient who may be fructose intolerant is empiric dietary fructose restriction. Products listing "fructose" or "crystalline fructose" (not "high-fructose corn syrup") as an ingredient should be eliminated. Juices/fruits containing excess fructose and products listing "high-fructose corn syrup" as an ingredient should be consumed in their recommended serving size (nondiet fountain drinks limited to 12 ounces), with a meal, and without sugar alcohols (unless naturally occurring) or lactose (if lactose intolerant). Perhaps, it is reasonable to initially limit ingestion to a maximum of two servings of all foods and beverages containing excess fructose per meal. If symptoms persist despite these restrictions and fructose intolerance is still suspected, a trial eliminating all HFCS items, as well as natural sources of excess fructose would be appropriate.American Journal of Gastroenterology Volume 99 Issue 10 Page 2046 - October 2004 doi:10.1111/j.1572-0241.2004.40266.x Dietary Fructose and Gastrointestinal Symptoms: A Review Suzanne M. Skoog, M.D., and Adil E. Bharucha, M.D.
 

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Discussion Starter · #4 ·
Welcome! What I found interesting was that HCFS was not as bad as it is made out to be. That there are two types of HCFS and that they don't usually mention what type of HCFS is in any given food. Even using the worst case scenario HCFS found in a serving of pop has only 5 gms of fructose in excess which could be unabsorbed.
 

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Discussion Starter · #5 ·
Welcome! What I found interesting was that HCFS was not as bad as it is made out to be. That there are two types of HCFS and that they don't usually mention what type of HCFS is in any given food. Even using the worst case scenario HCFS found in a serving of pop has only 5 gms of fructose in excess which could be unabsorbed.
 
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