REF-880 · Mettler et al., 2010 · Medicine & Science in Sports & Exercise, Vol. · Paper · PubMed

Increased Protein Intake Reduces Lean Body Mass Loss during Weight Loss in Athletes

B+moderate evidenceMeasured on recreational to trained athletesWritten before October 2026, being re-checked

Twenty young healthy resistance-trained athletes had their energy expenditure measured for a week, ate a mixed diet (15% protein, 100% energy) in the second week, then ate 60% of their habitual energy intake for 2 weeks with either ~15% protein (~1.0 g/kg; control) or ~35% protein (~2.3 g/kg; high protein), while continuing their usual training.

The control group lost more total mass and much more lean body mass than the high-protein group. Fat loss, performance and most blood markers did not differ between diets. The high-protein group reported more fatigue and more "worse than normal" scores on a daily stress questionnaire.

The authors conclude that ~2.3 g/kg protein was superior to ~1.0 g/kg for keeping lean body mass during short-term hypoenergetic weight loss.

Participants

n=20 young healthy resistance-trained athletes (MEDLINE indexing: male); control group (CP) n = 10, high-protein group (HP) n = 10.

Protocol

Week 1: energy expenditure measured.
Week 2: mixed diet, 15% protein, 100% energy.
Weeks 3-4: hypoenergetic diet at 60% of habitual energy intake:
CP: 15% protein (approximately 1.0 g x kg(-1))
HP: 35% protein (approximately 2.3 g x kg(-1))
Habitual training continued throughout.
Measured at the end of each of the 4 wk: total, lean and fat mass; squat jump, maximal isometric leg extension, 1RM bench press, bench-press muscle endurance, 30-s Wingate; fasting blood markers; psychological measures.

Key Results

CP (~1.0 g/kg)HP (~2.3 g/kg)P
Total mass change-3.0 ± 0.4 kg-1.5 ± 0.3 kg0.036
Lean body mass change-1.6 ± 0.3 kg-0.3 ± 0.3 kg0.006
The diet made no difference to fat loss, performance or most blood parameters.
Urea was higher in HP; NEFA and urea showed a group x time interaction.
Fatigue ratings, and "worse than normal" scores from a Daily Analysis of Life Demands for Athletes questionnaire, came out higher in HP.

Practical Application

In 20 resistance-trained young athletes eating 60% of their usual energy for 2 weeks, raising protein from ~1.0 to ~2.3 g/kg (15% to 35% of energy) cut lean-mass loss from 1.6 to 0.3 kg (P = 0.006), with the same fat loss and no difference in performance. To "should I eat more protein while I cut weight?": yes — at around 2.3 g/kg during a steep short deficit, about four fifths of the weight lost was not lean mass, versus about half of it at ~1.0 g/kg.
Performance did not differ between diets over the two weeks; the benefit here is body composition.
The high-protein group reported more fatigue and more "worse than normal" days; the abstract does not explain why, so say it rather than dismiss it.
Inference, not tested here: an energy cut this steep for an endurance athlete in a training block is a low-energy-availability risk regardless of protein; this trial answers what protein does inside a deficit, not whether the deficit is wise.
Not from this paper; the base's own practice: SYNTH-54 screens for low energy availability first and prefers a slow cut; protein targets in a deficit are also in REF-879 and REF-578.

Limitations

n=20 (10 per group), young resistance-trained men; 2-week deficit only.
Protein and carbohydrate/fat shares changed together, as the diets were isoenergetic with different protein percentages.
Lean body mass by body-composition measurement includes water and glycogen, not only muscle.
Written from the abstract and record metadata only (full text not read).
How this entry was checked and changed
Why this level

parallel RCT, n=20

Content correction 2026-09-27
2026-10-01: independent check against the abstract — wording brought back to what the abstract states.