Controlled studies on the effect of exercise on intestinal uptake of protein are scarce and underlying mechanisms largely unclear. We studied the uptake of the major allergen Ara h 6 following peanut consumption in an exercise model and compared this with changes in markers of intestinal permeability and integrity. Ten overnight-fasted healthy non-allergic men (n = 4) and women (n = 6) (23 +/- 4 years) ingested 100 g of peanuts together with a lactulose/rhamnose (L/R) solution, followed by rest or by 60 min cycling at 70% of their maximal workload. Significantly higher, though variable, levels of Ara h 6 in serum were found during exercise compared to rest (Peak p = 0.03; area under the curve p = 0.006), with individual fold changes ranging from no increase to an increase of over 150-fold in the uptake of Ara h 6. Similarly, uptake of lactulose (2–18 fold change, p = 0.0009) and L/R ratios (0.4–7.9 fold change, p = 0.04) were significantly increased which indicates an increase in intestinal permeability. Intestinal permeability and uptake of Ara h 6 were strongly correlated (r = 0.77, p