Insulin is an essential hormone that regulates glucose, amino acid and lipid homeostasis in both the fasting and fed states. Following consumption of a typical carbohydrate containing meal, blood glucose rises, leading to increased insulin secretion and hence in the stimulation of tissue glucose uptake and inhibition of liver (endogenous) glucose production. This conserved metabolic response is critical to preventing the excessive build-up of glucose in the body following a meal. Interestingly, when a high protein-carbohydrate free meal is consumed, insulin secretion is stimulated, yet blood glucose remains unaltered. While this phenomenon is well known, the mechanisms keeping blood glucose constant under such conditions are unclear, as theoretically, the protein-induced insulin secretion should cause blood glucose to drop, yet this has been extensively documented to not occur. Accordingly, in humans, using a unique multiple-meal protein feeding approach, combined with whole-body stable isotope biochemical flux tracing and quantitative targeted plasma metabolomics (across electron ionization and chemical ionization GC-MS platforms), we unambiguously uncovered the mechanisms responsible for this evolutionarily conserved metabolic phenomenon. Our results provide fundamental insight into the complex whole-body and tissue specific endocrine and metabolic regulatory mechanisms that have evolved to simultaneously fuel the energy needs of the human body while also permitting macronutrient storage for future energy reserves.