![]() ![]() The disorder is inherited in an autosomal recessive fashion and results from defects in the sucrase-isomaltase gene. ![]() Sucrase-isomaltase deficiency presents with gaseous symptoms after sucrose ingestion, usually in infancy. Finally, rare hereditary sugar intolerance syndromes are described. 13 Other potentially malabsorbed carbohydrates include isomalt, xylitol, and (rarely) sucrose. Sorbitol, a natural substance in fruits and an artificial sweetener, is malabsorbed by 43% of whites and 55% of nonwhites at doses as low as 5 grams. 12 Fructose-intolerant patients pass flatus more frequently and produce more hydrogen for given amounts of fructose versus asymptomatic individuals. Increased gas production occurs after consuming fructose-containing fruits, juices, and soft drinks with a threshold of 37.5 grams of fructose. Forty percent of fructose is not absorbed in the normal human intestine. 11 Impaired assimilation of other simple sugars produces gaseous symptoms as well. 10 Individuals with lactose intolerance rarely experience symptoms unless more than 240 mL of milk are ingested per day. Lactase deficiency occurs in 21% of nonhispanic whites but is more prevalent in those of African (75%), Hispanic (51%), and Native American (79%) background. Intolerance of Simple Sugars The most common carbohydrate maldigestion syndrome, lactose intolerance, results from insufficient levels of enterocyte lactase, which hydrolyzes lactose into glucose and galactose. Carbohydrate intolerance results from loss of enterocyte enzymes in normal intestinal mucosa, inability to transport a poorly absorbed sugar across normal enterocyte membranes, or organic mucosal disorders such as celiac disease. Unabsorbed carbohydrates are propelled to the colon and serve as nutrient substrates for enteric bacteria, liberating hydrogen gas and short-chain fatty acids. Maldigestion and malabsorption of simple and complex carbohydrates and dietary fiber are commonly associated with gas and bloating. 5 Gas transit is accelerated by liquid or solid meals, providing an experimental correlate to the observation that gas passage and gaseous symptoms increase postprandially. 4 Gas collected from the rectum in such studies is expelled in pulsatile fashion, indicating that flow is regulated by intrinsic motor patterns in the distal gut. In healthy volunteers, gas perfusion produces steady state flow with little distention and few symptoms. ![]() Insight into normal patterns of intestinal gas transit has been provided by experiments in which physiologic gas mixtures containing nitrogen, oxygen, and carbon dioxide are perfused into the jejunum. ![]() 3 Men produce more aromatic flatus than women. Other sulfur-containing gases in flatus include methanetriol and dimethyl sulfide. Flatus odor correlates with hydrogen sulfide concentrations. 2 Gases produced by colonic bacterial fermentation of ingested nutrients and endogenous glycoproteins (hydrogen, methane, and carbon dioxide) represent 74% of flatus. The major gases in flatus are nitrogen, oxygen, carbon dioxide, hydrogen, and methane. Flatus rates up to 25 per day are normal. 1 On average, healthy men pass flatus 14 times per day, especially after meals. The gastrointestinal tract contains, on average, less than 200 mL of gas, whereas daily gas expulsion averages 600–700 mL. Available therapies include lifestyle alterations, dietary modifications, enzyme preparations, adsorbents and agents which reduce surface tension, treatments that alter gut flora, and drugs that modulate gut transit. Treatment of gaseous symptomatology should be targeted to pathophysiologic defects whenever possible. The evaluation of the patient with unexplained gas and bloating relies on careful exclusion of organic disease with further characterization of the underlying condition with directed functional testing. Because of the prominence of gaseous complaints in IBS, recent investigations have focused on new insights into pathogenesis and novel therapies of bloating. There are many causes of gas and bloating including aerophagia, luminal obstructive processes, carbohydrate intolerance syndromes, small intestinal bacterial overgrowth, diseases of gut motor activity, and functional bowel disorders including irritable bowel syndrome (IBS). Gaseous symptoms including eructation, flatulence, and bloating occur as a consequence of excess gas production, altered gas transit, or abnormal perception of normal amounts of gas within the gastrointestinal tract. ![]()
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