Malabsorption Fructose

several studies have measured intestinal absorption of fructose using hydrogen breath test. these studies indicate fructose not absorbed in small intestine. when fructose not absorbed in small intestine, transported large intestine, fermented colonic flora. hydrogen produced during fermentation process , dissolves blood of portal vein. hydrogen transported lungs, exchanged across lungs , measurable hydrogen breath test. colonic flora produces carbon dioxide, short-chain fatty acids, organic acids, , trace gases in presence of unabsorbed fructose. presence of gases , organic acids in large intestine causes gastrointestinal symptoms such bloating, diarrhea, flatulence, , gastrointestial pain exercise after consumption can exacerbate these symptoms decreasing transit time in small intestine, resulting in greater amount of fructose emptied large intestine.