Our objective was to quantify effects of increases among small intestinal starch digestion in response to greater postruminal flows of glutamic acid (Glu) on N retention. Five steers (351 ± 11 kg BW) were fed (5.1 ± 0.06 kg DM/d) a soybean hull-based diet formulated to provide adequate ruminally available N, moderate amounts of RUP, and small amounts of starch (0.8% DM). Cattle were placed in a 5 × 5 Latin square with 12-d periods. Cattle received (DM basis) continuous duodenal infusion of raw cornstarch (1.5 ± 0.08 kg/d), and either 0 (control), 30.9 ± 0.59, 62.4 ± 1.16, 120.4 ± 3.39 g/d Glu or 407 ± 18.3 g/d casein (a positive control). Data were analyzed with Mixed procedures of SAS; linear and quadratic effects of Glu were determined and the positive control was compared with the negative control by a t test. Nitrogen intake from feed was not different (P ≥ 0.23). Infusate N increased from 0 to 13 g/d with greater amounts of Glu (Linear < 0.01) and casein provided 61 g N/d (P < 0.01). Similarly, total N intake was greater when cattle were provided casein (P < 0.01), but was not affected by Glu (Linear = 0.75). Increases in postruminal Glu did not affect urinary N excretion (P ≥ 0.30), but casein increased urinary N excretion (P < 0.01). Fecal N excretion was not different (P ≥ 0.55) despite reduced ileal flow of starch in response to greater postruminal flows of Glu (Linear = 0.04) or casein (P = 0.07). Glutamic acid had little impact on N retention (P ≥ 0.95) despite increases in small intestinal starch digestion (Linear = 0.02), but casein increased N retention (P < 0.01). It is possible that increases in energy available for gain from increased small intestinal starch digestion in response to greater postruminal flow of Glu are used for purposes other than protein gain; however, it is likely that increases in energy available for gain exceeded capabilities for N deposition under conditions of our experimental model, because N retained as a proportion of N intake was not different when cattle were provided Glu (P ≥ 0.83) or casein (P = 0.38).