The Keto Protein Floor: Mathematical Calculation & Lean Mass Preservation

1. Lean Body Mass vs. Total Weight: The Katch-McArdle Equation

Setting protein targets as a flat percentage of total daily calories (e.g. '15% protein') is fundamentally flawed. If a 110kg individual with 35% body fat eats at a 1,600 kcal deficit, a 15% allocation yields only 60g of protein — leading directly to sarcopenic muscle loss.

Repast anchors protein to Lean Body Mass using the Katch-McArdle formulation: LBM = Total Body Mass × (1 − Body Fat Percentage). Your physiological protein floor is set between 1.6g and 2.2g per kilogram of LBM (0.75g–1.0g per pound).

A 90kg individual with 25% body fat has 67.5kg of lean tissue. Their absolute daily protein floor is 108g to 148g, regardless of caloric deficit.

2. The Sarcopenia Hazard on Deficit: Why Percentage Ratios Fail

When the body operates in an energy deficit, skeletal muscle tissue is vulnerable to proteolysis. Amino acids are cleaved from muscle fibers to maintain circulating plasma albumin, immunoglobulins, and basal nitrogen balance.

Consuming adequate dietary protein spares skeletal muscle by providing exogenous amino acids for systemic maintenance. Restricting protein during fat loss causes the body to consume its own contractile machinery, slowing resting metabolic rate (RMR) and leading to the dreaded 'skinny fat' phenotype.

Preserving 5kg of skeletal muscle tissue burns approximately 65–100 additional kilocalories per day at rest and dramatically improves postprandial glucose disposal via non-insulin-mediated GLUT-4 translocation.

3. The 3.0g Leucine Threshold & mTOR Muscle Protein Synthesis

Muscle protein synthesis (MPS) is not a linear continuum; it operates as an on-off switch mediated by the essential branched-chain amino acid leucine. Each meal sitting must deliver approximately 2.5g to 3.0g of leucine to trigger the mammalian target of rapamycin (mTOR) pathway.

In whole-food terms, this equates to roughly 30g to 40g of intact animal protein per meal. Grazing on 10g protein snacks throughout the day fails to reach the intracellular threshold needed to preserve lean skeletal mass.

Spacing two or three 35g–45g protein meals across your day guarantees multiple pulses of muscle protein synthesis while keeping insulin low and manageable.

4. Hepatic Biochemistry: Dispelling the Gluconeogenesis Myth

Rumors that 'excess protein turns into sugar and kicks you out of ketosis' misrepresent basic biochemistry. Hepatic gluconeogenesis is an endothermic, demand-driven process regulated by glucagon-to-insulin ratios and cellular energy status, not an unconstrained supply-driven spigot.

The liver synthesizes glucose only at the rate required to supply obligate glycolytic tissues (red blood cells and the renal medulla). Eating an extra chicken breast does not cause a surge in circulating glucose. Clinical trials consistently demonstrate that high-protein ketogenic diets maintain deep nutritional ketosis while dramatically improving satiety.