Relative Protein Intake and Physical Function in Older Adults: A Systematic Review and Meta-Analysis of Observational Studies

Abstract

(1) Background: The present work aims to conduct a systematic review and meta-analysis of observational studies, in order to investigate the association of relative protein intake and physical function in older adults; (2) Methods: Observational studies, that investigated the association between protein intake and physical function in older adults, were retrieved from MEDLINE, SCOPUS, CINAHL, AgeLine, EMBASE, and Cochrane-CENTRAL. Two independent researchers conducted study selection and data extraction; (3) Results: Very high protein intake (≥1.2 g/kg/day) and high protein intake (≥1.0 g/kg/day) groups showed better lower limb physical functioning and walking speed (WS) performance, respectively, in comparison to individuals who present relative low protein (<0.80 g/kg/day) intake. On the other hand, relative high protein intake does not seem to propitiate a better performance on isometric handgrip (IHG) and chair rise in comparison to relative low protein intake. In addition, there were no significant differences in the physical functioning of high and middle protein intake groups; (4) Conclusions: In conclusion, findings of the present study indicate that a very high (≥1.2 g/kg/day) and high protein intake (≥1.0 g/kg/day) are associated with better lower-limb physical performance, when compared to low protein (<0.80 g/kg/day) intake, in community-dwelling older adults. These findings act as additional evidence regarding the potential need to increase protein guidelines to above the current recommendations. However, large randomized clinical trials are needed to confirm the addictive effects of high-protein diets (≥1.0 g/kg/day) in comparison to the current recommendations on physical functioning. All data are available in the Open ScienceFramework.

Keywords: physical function; protein intake; sarcopenia.

Figure 1

Flowchart of the present study.

Figure 2

Mean difference in (a) Upper-limb muscle strength and Standardized mean difference in (b) Lower-limb muscle strength according to protein intake. Squares represent study-specific estimates; diamonds represent pooled estimates of random-effects meta-analyses.

Figure 3

Mean differences in Mobility according to protein intake. (a) Chan et al., 2014, and Isanejad et al., 2016; (b) Chan et al., 2014b, and Isanejad et al., 2016; (c) Chan et al., 2014ab, and Isanejad et al., 2016; (d) Chan et al., 2014c, and Isanejad et al., 2016; (e) Chan et al., 2014abc, and Isanejad et al., 2016. Squares represent study-specific estimates; diamonds represent pooled estimates of random-effects meta-analyses.

Figure 4

Mean difference in (a) Upper-limb muscle strength; (b) Mobility; and (c) Lower-limb muscle strength according to protein intake. Squares represent study-specific estimates; diamonds represent pooled estimates of random-effects meta-analyses.

Figure 5

Standardized mean difference in Lower-limb muscle functioning according to protein intake. Squares represent study-specific estimates; diamonds represent pooled estimates of random-effects meta-analyses.