Effect of dietary protein content on weight gain, energy expenditure, and body composition during overeating: a randomized controlled trial.
Level 2 - randomized trial
Individual randomized controlled trial
PubMed 22215165 · doi:10.1001/jama.2011.1918
What was done
A single-blind randomized controlled trial evaluated the effects of overfeeding low-, normal-, and high-protein diets in 25 healthy, weight-stable adults aged 18 to 35 years (BMI 19–30) residing in an inpatient metabolic unit. After a 13- to 25-day weight-stabilization period, participants were overfed by ~40% excess energy (954 kcal/d; 95% CI, 884–1022 kcal/d) for 8 weeks with diets containing 5% (low protein), 15% (normal protein), or 25% (high protein) energy from protein. Body composition was assessed biweekly by DXA, resting energy expenditure was measured weekly by ventilated hood, and total energy expenditure was measured by doubly labeled water.
What was found
Overeating produced significantly less weight gain in the low-protein group (3.16 kg; 95% CI, 1.88–4.44 kg) compared with normal-protein (6.05 kg; 95% CI, 4.84–7.26 kg) and high-protein groups (6.51 kg; 95% CI, 5.23–7.79 kg; P = .002). However, body fat increased similarly across all three groups, accounting for 50% to >90% of excess stored calories. Resting energy expenditure, total energy expenditure, and body protein did not increase in the low-protein group. In contrast, resting energy expenditure increased significantly with normal protein (160 kcal/d; 95% CI, 102–218 kcal/d) and high protein (227 kcal/d; 95% CI, 165–289 kcal/d), as did lean body mass (normal protein: 2.87 kg [95% CI, 2.11–3.62 kg]; high protein: 3.18 kg [95% CI, 2.37–3.98 kg]).
Why it matters
Under strictly controlled overfeeding conditions, calorie intake alone drives fat mass accumulation, whereas dietary protein level dictates the accretion of lean mass and changes in metabolic rate.
Limits
The sample size was small (25 total participants across three intervention arms). The study evaluated young, healthy adults in a short-term (8-week overfeeding), strictly controlled inpatient setting, which limits generalizability to free-living conditions, older demographics, or clinical populations.
Cited by
- contradicts The human body cannot store excess protein, converting surplus intake into fat.