RATIONALE: Currently there is no consensus on protein requirements for obese older adults during weight loss. Here we explore the potential use of a new method for assessment of protein requirements based on changes in appendicular muscle mass during weight loss.

METHODS: 60 obese older adults were subjected to 13 wk weight loss program, including hypocaloric diet and resistance training. Assessment of appendicular muscle mass was performed by DXA at baseline and after 13 wk challenge period, and the difference calculated as muscle mass change. Protein intake (g/kg body weight and g/kg fat free mass (FFM)) at 13wks was used as marker of protein intake during 13 wk period. 30 subjects received 10 times weekly 20 g protein supplement throughout the 13 week hypocaloric phase which is included in the calculation of total protein intake. Receiver operating characteristic (ROC) curve analysis was used to explore the optimal cutoff point for protein intake (g/kg) versus increase in appendicular muscle mass of more than 250 g over 13 wks (y/n). Subsequently, logistic regression analysis was performed for protein intake cutoff and muscle mass accretion, adjusted for sex, age, baseline BMI, and training compliance.

RESULTS: ROC curve analysis provided a protein intake level per day of 1.2 g/kg bw and 1.9 g/kg FFM as cutoff point. Presence of muscle mass accretion during 13 wk challenge period was significantly higher with protein intake higher than 1.2 g/kg bw (OR 5.4, 95%CI 1.4-20.6, p = 0.013) or higher than 1.9 g/kg FFM (OR 8.1, 95%CI 2.1-31.9, p = 0.003). Subjects with a protein intake higher than 1.2 g/kg had significantly more often muscle mass accretion, compared to subjects with less protein intake (10/14 (72%) vs 15/46 (33%), p = 0.010). For 1.9 g/kg FFM this was 70% vs 28% (p = 0.002).

CONCLUSION: This exploratory study provided a level of at least 1.2 g/kg body weight or 1.9 g/kg fat free mass as optimal daily protein intake for obese older adults under these challenged conditions of weight loss, based on muscle mass accretion during the challenge.

TRIAL REGISTRATION: Dutch Trial Register under number NTR2751.