Eating protein after working out doesn't make your body burn more protein as fuel than it needs for building muscle - most of the protein goes toward building muscle instead of being burned for energy.
Scientific Claim
Protein ingestion does not significantly increase whole-body amino acid oxidation rates relative to the increase in whole-body protein synthesis rates in healthy young men after resistance exercise.
Source Excerpt
“However, the concurrent increase in amino acid oxidation rates was negligible when compared to the whole-body protein synthetic response (Figure 2J). Collectively, this resulted in a strong positive correlation between protein intake and whole-body protein net balance (Figure 2L).”
Evidence from Studies
Supporting Studies
The anabolic response to protein ingestion during recovery from exercise has no upper limit in magnitude and duration in vivo in humans
The study measured whole-body protein synthesis and amino acid oxidation rates using isotope tracers. The data showed that while both increased with protein intake, the oxidation rates were negligible relative to the synthesis rates, indicating minimal protein burning for energy.