Incomplete absorption of pure fructose in healthy subjects and the facilitating effect of glucose.

Small-intestinal absorption of fructose was investigated in healthy human subjects by sequential breath-hydrogen measurements. Fifty-eight percent of 103 subjects produced greater than 20 microL H2/L after consuming 50 g pure fructose in water. About half of those who absorbed fructose incompletely (incomplete absorbers) had abdominal symptoms. Malabsorption of medium doses of pure fructose may therefore be common in man. When 25 g pure fructose was consumed, only 19% of 21 poor absorbers (of 50 g fructose) still produced excess breath H2. When glucose was taken with fructose, the frequency and amount of excessive breath H2 was substantially reduced. This facilitating phenomenon is not generally known but is important because in natural foods fructose occurs in association or in combination (as sucrose) with glucose. Plasma fructose responses were not lower in poor absorbers presumably because these responses depend more on how much fructose passes through the liver than on how much is absorbed.