Effects of an increased habitual dietary protein intake followed by resistance training on fitness, muscle quality and body composition of seniors: a randomised controlled trial

Background & Aims Resistance training and a sufficient amount of dietary protein have been suggested to build up and maintain muscle mass, strength and function into old age. As there is still no consensus on the optimum amount of protein intake in older people, this study aims to evaluate first whether it is achievable to double the recommended amount, which is 1 g/kg BW/d in German speaking countries, via food administration and secondly whether this would lead to stronger improvements when subsequently combined with resistance training. Methods In total, 136 community-dwelling older adults (54% females, 72.9 ± 4.8 yrs) were randomly assigned to one of the three study groups: observational control (CON), recommended protein (RP+T) and high protein (HP+T) intake groups. After six weeks of observation or nutritional counselling to achieve the respective protein target levels, eight weeks of resistance training (2x/week) were applied in RP+T and HP+T groups. Parameters indicative for muscle mass, strength and function were measured at baseline (t1), before (t2) and after the training period (t3). Results Baseline protein intake for the different groups were 0.83 (CON), 0.97 (RP+T) and 0.78 (HP+T) g/kg BW/d and increased by 0.18 ± 0.31 (RP+T, p = 0.003) and 0.83 ± 0.33 (HP+T, p > 0.001) g/kg BW/d between t1 and t3 while CON remained unchanged. Most of the physical performance parameters improved over time, but no interaction effects between group and time could be observed. While body fat mass initially increased from t1 to t2 (0.8 ± 2.3 kg, p = 0.001), skeletal muscle mass decreased (-0.5 ± 1.9 kg, p = 0.025), a trend which was reversed from t2 to t3 only in HP+T group (body fat mass: -0.47 ± 2.12 kg, p = 0.041; muscle mass: 0.51 ± 1.57 kg, p = 0.021). Conclusion The findings suggest that a substantial increase of habitual protein intake above the currently recommended levels is achievable within 17 weeks in community-dwelling older adults, whereby the extra amount of protein led to minor changes in body composition but not physical performance or muscle quality (NCT04023513).