In humans, the effects of lysine-fortified wheat on growth measures was much lower than that of animal experimentations that used phosphorus-containing mineral mix. It is known that wheat contains a limited amount of available phosphorus, which is believed to support growth. The aim of this study was to determine the involvement of phosphorus in growth measures of rats maintained on a lysine-supplemented wheat gluten diet. Forty male Sprague-Dawley (6 wk old) rats were randomly divided into four equal groups and fed wheat gluten protein (10%)-based diets with added lysine (0.6%), phosphorus (0.3%), or both (0.6% lysine and 0.3% phosphorus), ad libitum for 9 wk. Rats were monitored for changes in food intake, body weight, body and liver compositions, plasma urea nitrogen, and albumin. The addition of lysine or phosphorus to wheat gluten-based diets increased energy intake modestly (∼15%), whereas their combination caused a higher increase (∼45%). Similarly, the magnitude of improvement in weight gain and energy efficiency by the addition of lysine or phosphorus (∼1g/d and 2.7g/MJ, respectively) was much lower than that of the combination (∼4g/d and 8.7g/MJ). In the phosphorus-containing groups, plasma urea nitrogen was significantly reduced and this was associated with higher body protein (%) and hepatic fat (%); whereas plasma albumin was significantly increased in the lysine-containing groups. When using gluten protein, concomitant lysine and phosphorus availability is required to support growth measures, although phosphorus seems to have an independent effect on protein metabolism. Thus, human interventions should consider the improvement of the amino acid profile and phosphorus availability.