Protein-Sparing in a Caloric Deficit

When energy intake is below expenditure, the body can break down both fat and lean (muscle) tissue for fuel. The goal of a fat-loss phase is to lose fat while sparing muscle. Two levers protect lean mass:

1. Higher protein. The ISSN reports that 2.3–3.1 g/kg of body weight per day maximizes retention of lean mass in resistance-trained individuals during hypocaloric (deficit) periods — higher than the 1.4–2.0 g/kg sufficient at maintenance (see protein). Leaner individuals and larger deficits push toward the top of that range. Protein also has the highest thermic effect and is the most satiating macronutrient, aiding adherence.
2. Resistance training. Continuing to train hard signals the body to keep muscle; without a strength stimulus, more of the weight lost is lean tissue (see progressive-overload, muscle-hypertrophy).

Other supports: keep the deficit moderate (~0.5–1% body weight/week — see safe-deficit-rate), get adequate sleep, and don't crash-diet — aggressive deficits with low protein and no resistance training are the classic recipe for losing muscle along with fat. These principles define the "cut" (see cutting).

• Deficits can burn muscle as well as fat; goal is to spare lean mass.
• ISSN: 2.3–3.1 g/kg/day protein maximizes lean retention while cutting (trained people).
• Higher protein also boosts satiety and thermic effect, aiding adherence.
• Resistance training is essential to signal muscle retention.
• Keep deficit moderate (~0.5–1% body weight/week) and sleep adequately.

• protein — baseline vs. deficit protein needs.
• calorie-targets — setting the deficit.
• fat-loss-nutrition / cutting — applying these in a fat-loss phase.
• muscle-hypertrophy — training stimulus that preserves muscle.