“Dietary protein-derived amino acids have a purpose, and that purpose is not carbs.”
At a reasonable level of dietary intake, protein is used for the maintenance of organs & tissues. Lean body mass. It’s functional. Protein isn’t stored in any appreciable capacity, and most excess is either oxidized or stored as glycogen. Theoretically, about 50-60% of protein-derived amino acids can be converted into glucose, mathematically, but it’s not what you think…
“At a reasonable level of dietary intake.” A recent publication took a look at this (Fromentin et al., 2013). They set out to determine how much protein is converted to glucose under “optimal gluconeogenic conditions.” That is, the subjects were 12 hours fasted, which is a physiologically relevant, optimal gluconeogenic condition. They were then given 4 eggs (~23 g protein) that were labeled with two stable isotopes (15N & 13C, derived from hens fed isotope-enriched diets!). Throughout the entire study duration, the subjects were infused with a third isotope, 2H-glucose. By collecting and analyzing the enrichment of isotopically-labeled metabolites like expired CO2, urea, and glucose, the researchers were able to determine the fate of those 23 grams of protein.
Some of the dietary protein-derived amino acids were used for protein synthesis, others were oxidized. But blood glucose levels did not change. Nor did the rate of gluconeogenesis.