How is fructose (mal)absorbed?
The mechanism of fructose absorption is not completely understood. It is proposed that fructose is absorbed by a facilitated transport mechanism via a carrier, but not against a concentration gradient. Another hypothesis (and a mechanism that could operate at the same time as the one described above) is that fructose is absorbed by a disaccharidase-related transport system. This is surmised because the absorption of fructose is more efficient in the presence of glucose, with maximal absorption occurring when fructose and glucose are present in equimolar concentrations. The absorption capacity of fructose is much more complete when fructose is given either as sucrose to be broken down or with glucose than when it is ingested alone. Clinical studies have demonstrated this, with malabsorption being more apparent when the fructose concentration exceeds that of glucose (e.g., in apple and pear juice) than when the 2 sugars are present in equal concentrations (e.g., in white grape juice). Ho
