Ability of the Normal Human Small Intestine to Absorb Fructose: Evaluation by Breath Testing

Background & Aims: Fructose consumption is increasing, and its malabsorption causes common gastrointestinal symptoms. Because its absorption capacity is poorly understood, there is no standard method of assessing fructose absorption. We performed a dose-response study of fructose absorption in healthy subjects to develop a breath test to distinguish normal from abnormal fructose absorption capacity. Methods: In a double-blind study, 20 healthy subjects received 10% solutions of 15, 25, and 50 g of fructose and 33% solution of 50-g fructose on 4 separate days at weekly intervals. Breath samples were assessed for hydrogen (H₂) and methane (CH₄) during a period of 5 hours, and symptoms were recorded. Results: No subject tested positive with 15 g. Two (10%) tested positive with 25 g fructose but were asymptomatic. Sixteen (80%) tested positive with 50 g (10% solution), and 11 (55%) had symptoms. Breath H₂ was elevated in 13 (65%), CH₄ in 1 (5%), and both in 2 (10%). Twelve (60%) tested positive with 50 g (33% solution), and 9 (45%) experienced symptoms. The area under the curve for H₂ and CH₄ was higher (P < .01) with 50 g compared with lower doses. There were no gender differences. Conclusions: Healthy subjects have the capacity to absorb up to 25 g fructose, whereas many exhibit malabsorption and intolerance with 50 g fructose. Hence, we recommend 25 g as the dose for testing subjects with suspected fructose malabsorption. Breath samples measured for H₂ and CH₄ concentration at 30-minute intervals and for 3 hours will detect most subjects with fructose malabsorption.