Lean mass preservation

Keeping muscle while losing fat: the part rapid weight loss threatens.

Lean mass preservation is the aim of losing fat while keeping as much muscle as possible. Weight loss without it leaves you lighter, weaker and with a lower resting metabolic rate, which is a worse outcome than the scale suggests.

Two interventions have the strongest evidence and they are unglamorous. Adequate protein, at the upper end of the range in a deficit, and continued resistance training. Together they shift the composition of the weight lost substantially towards fat.

Deficit size is the third variable. Large aggressive deficits increase the proportion of lean tissue lost, particularly in people who are already lean, which is the practical argument for a moderate rate even when a faster one is possible.

It has become a prominent question in the era of GLP-1 medicines. Body composition substudies and reviews find lean tissue makes up a substantial fraction of the total weight lost, broadly in line with what any large energy deficit does, which is exactly why protein intake and resistance training matter more during pharmacological weight loss rather than less.

Age raises the stakes. Older adults lose muscle more readily and rebuild it more slowly, so a period of rapid weight loss without training can cost function that takes far longer to recover than it took to lose.

Measurement is the frustrating part, since bathroom scales estimating body composition are unreliable and DEXA is not weekly. Strength in the gym is a decent proxy: if the loads are holding while the weight falls, the composition is probably going the right way.

In practice, set protein high with our calculator, keep lifting through the diet, and prefer a slower rate you can sustain.

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