One major goal of nutrition is to maximize the rate of muscle protein gain via provision of amino acids (AAs) through blood plasma. Comparing the plasma AA concentrations with the growth performance data can help to elucidate the metabolic mechanisms regulating plasma AA homeostasis, nutrient utilization, and intracellular protein turnover. Knowledge about the homeostatic regulation of plasma AA profile can aid in predicting dietary AA availabilities, the order of limiting AAs, and the whole body protein metabolism. Lysine, for example, is typically the first limiting AA in practical swine diets; however, our current knowledge is insufficient to draw a clear conclusion about the complex relationship between dietary lysine supply and plasma AA profiles. Thorough understanding of the effect of dietary AA supply on plasma AA profiles can help nutritionists to develop novel nutritional strategies to guide and improve dietary AA supplies. Further research is needed to study how different levels of dietary AAs, individually or in concert, affect the plasma concentrations of all AAs and related metabolites.