The effect of ketone bodies and dietary carbohydrate intake on protein metabolism.
Level 3 - non-randomized controlled study
Non-randomized metabolic infusion and dietary comparative intervention study in human cohorts
What was done
Researchers evaluated the effect of beta-hydroxybutyrate infusions (producing 1–2 mM blood ketone increments) on protein metabolism in healthy nonobese subjects, obese subjects, and individuals with insulin-dependent diabetes in the postabsorptive state, as well as obese subjects fasted for 3 days and 3–10 weeks. They measured changes in plasma alanine and tracked urinary nitrogen during repeated 12-hour infusions in subjects fasted 5–10 weeks. They also examined endogenous ketonemia from isocaloric carbohydrate restriction (<25 g/day) on plasma branched-chain amino acids and insulin after protein ingestion and intravenous leucine, and compared nitrogen balance between hypocaloric (400 kcal) pure protein and 50% protein / 50% carbohydrate diets.
What was found
Beta-hydroxybutyrate infusion reduced plasma alanine by 25–35% across all treatment groups, including in fasted subjects. Repeated 12-hour infusions in prolonged fasted subjects reduced urinary nitrogen by 30%, which returned to baseline after stopping infusion. Carbohydrate restriction led to a 40–50% greater increase in postprandial branched-chain amino acids, reduced insulin secretion, and caused a 40% greater elevation in plasma leucine after intravenous leucine infusion. Nitrogen balance showed no significant differences between the 400 kcal pure protein diet and the 400 kcal mixed carbohydrate-protein diet.
Why it matters
The findings demonstrate that while ketones help spare muscle protein during prolonged starvation, carbohydrate restriction reduces insulin and impairs the net disposal of ingested protein, meaning ketogenic high-protein diets offer no unique protein-sparing advantage over mixed diets.
Limits
The abstract does not state the sample size (n), participant demographics, or exact p-values and confidence intervals. Long-term functional body composition outcomes were not assessed, and the comparisons rely on short-term surrogate metabolic measurements.
Cited by
- supports Intravenous infusion of beta-hydroxybutyrate in humans causes a sharp decrease in circulating alanine and preserves or elevates branched-chain amino acids such as leucine.