Dietary protein digestion and absorption are impaired during acute postexercise recovery in young men

Previously, we demonstrated that exercise can cause small intestinal injury, leading to loss of gut barrier function. The functional consequences of such exercise-induced intestinal injury on subsequent food digestion and absorption are unclear. The present study determined the impact of resistance-type exercise on small intestinal integrity and in vivo dietary protein digestion and absorption kinetics. Twenty-four young males ingested 20 g specifically produced intrinsically l-[1-(13)C]phenylalanine-labeled protein at rest or after performing a single bout of resistance-type exercise. Continuous intravenous infusions with l-[ring-(2)H5]phenylalanine were employed, and blood samples were collected regularly to assess in vivo protein digestion and absorption kinetics and to quantify plasma levels of intestinal fatty-acid binding protein (I-FABP) as a measure of small intestinal injury. Plasma I-FABP levels were increased after exercise by 35%, reaching peak values of 344 ± 53 pg/ml compared with baseline 254 ± 31 pg/ml (P < 0.05). In resting conditions, I-FABP levels remained unchanged. Dietary protein digestion and absorption rates were reduced during postexercise recovery when compared with resting conditions (P < 0.001), with average peak exogenous phenylalanine appearance rates of 0.18 ± 0.04 vs. 0.23 ± 0.03 mmol phenylalanine·kg lean body mass(-1)·min(-1), respectively. Plasma I-FABP levels correlated with in vivo rates of dietary protein digestion and absorption (rS = -0.57, P < 0.01). Resistance-type exercise induces small intestinal injury in healthy, young men, causing impairments in dietary protein digestion and absorption kinetics during the acute postexercise recovery phase. To the best of our knowledge, this is first evidence that shows that exercise attenuates dietary protein digestion and absorption kinetics during acute postexercise recovery.