Walking exercise alters protein digestion, amino acid absorption, and whole body protein kinetics in older adults with and without COPD.

PURPOSE Gut symptoms and markers of gut dysfunction have been observed in patients with Chronic Obstructive Pulmonary disease (COPD). It remains unclear whether walking exercise induces disturbances in protein digestion and amino acid absorption and whole body protein kinetics in these subjects due to exercise induced hypoxia. METHODS Sixteen clinically stable patients with moderate to very severe COPD and 12 age matched control subjects completed the study. Protein digestion and amino acid absorption and whole body protein kinetics, in the postabsorptive state, were measured via a continuous infusion of stable tracers in combination with orally administered tracer sips during 20 minutes of walking exercise and up to 4 hours post-exercise. COPD patients completed one study day, walking at maximal speed, while healthy subjects completed two, one matched to the speed of a COPD patient and one walking at maximal speed. RESULTS The COPD patients tolerated 20 minutes of vigorous intensity walking despite elevated heart rate (P<0.001) and substantial desaturation (P<0.001). Relative to rest, protein digestion was increased during recovery from exercise (P<0.05) while amino acid absorption was reduced during (P<0.0001) and immediately after exercise (P<0.001). Whole body protein breakdown was reduced within 20 minutes after exercise (P<0.05) and stayed suppressed for four hours (P<0.0001). Whole body net protein breakdown was elevated for four hours post-exercise (P<0.001). CONCLUSION Our data showed that 20 minutes of walking exercise is sufficient to cause substantial perturbations in gut function in older adults and COPD patients with hypoxia as a potential underlying factor.