BACKGROUND We previously reported microbial lysine contribution to plasma lysine homeostasis in humans with an adequate lysine intake. OBJECTIVE We sought to explore whether the low lysine intake from a wheat gluten-based diet is balanced by enhanced microbial lysine contribution in a pig model. METHODS Twenty miniature pigs (minipigs) fitted with ileo-ileal cannulas were fed 2 wheat gluten-based diets. One diet provided 2.7 g lysine/kg diet (WG diet) and one diet was supplemented with crystalline lysine to provide 6.6 g lysine/kg diet (WG+Lys diet). Both diets were fed for 10 or 100 d (n = 5 per group): 10WG+Lys, 10WG, 100WG+Lys, and 100WG diets. Ileal microbial lysine, which we considered to be the precursor pool for absorption, was labeled by oral administration of (15)NH(4)Cl for the final 10 d. On days 10 and 100, a 10-h fast-fed tracer protocol with [1-(13)C]lysine was performed. RESULTS Lysine rates of appearance decreased by 25% with the WG diet in the fed state but increased by 50% with the WG+Lys diet in the fasted state (P < 0.05). Daily gross microbial lysine contribution was lower (P < 0.05) with the WG diet (205.3 micro mol. kg(-) (1). d(-)(1)) than with the WG+Lys diet (370.7 micro mol. kg(-) (1). d(-)(1)), irrespective of the adaptation period and was similar to the ileal lysine loss with the WG diet. In the WG groups, incorporation of microbial lysine increased in the duodenum and liver (P < 0.05) but not in whole-body and muscle proteins. CONCLUSIONS Minipigs fed the WG diet did not adapt by showing an enhanced absorption of microbial lysine to the extrasplanchnic tissues, presumably because microbial lysine continues to be used for splanchnic protein synthesis.