Effect of protein consumption and supplementation on body composition and functional capacity in cardiovascular disease patients undergoing cardiovascular rehabilitation: A systematic review and meta-analysis

Cardiovascular diseases (CVD) remain the leading cause of death worldwide. Nutritional strategies, including protein intake, play a crucial role in cardiovascular rehabilitation by supporting overall health and recovery. This review explores the hypothesis that protein supplementation enhances muscle mass, leading to improved body composition and functional capacity in CVD patients. We conducted a systematic review of randomized controlled trials (RCTs) in accordance with the Cochrane Manual for Systematic Reviews of Interventions, with the protocol registered under CRD42022292687. A comprehensive search strategy, incorporating population, intervention, and study design terms, was executed across PubMed, EMBASE, Scopus, and Web of Science from data inception to February 1, 2024. Study quality was assessed using the Cochrane risk of bias tool (RoB 2.0), and meta-analysis was performed with statistical packages in Rstudio 3.6.2. From 10 939 initial citations, seven RCTs and three pilot RCTs met the eligibility criteria. Sample sizes ranged from 11 to 70 participants, with mean ages between 55 and 80 years. The narrative synthesis revealed mixed effects of protein supplementation on body composition and functional capacity. Lean body mass improvements were observed in several trials, particularly when protein intake was combined with resistance training. However, reductions in adipose tissue were inconsistent. Functional capacity enhancements—such as improved handgrip strength and 10-meter walk test performance—were observed in some trials, especially those using whey or leucine-enriched protein supplements. However, findings on VO₂ peak, a key indicator of exercise capacity, were inconclusive, some trials reporting improvements while others showed no significant effect. Risk of bias varied from low to high across trials, and heterogeneity in intervention types, protein dosages, and study durations limited direct comparisons. Outcomes classified with very low certainty of evidence included body mass index, the 6-minute walk test, and VO₂ peak or maximum. Meanwhile, low-certainty evidence was found for handgrip strength, fat mass, and lean body mass. In conclusion, while protein supplementation may support improvements in body composition and functional capacity, variability in protein types and dosages prevents a clear recommendation for CVD patients in cardiovascular rehabilitation. Further high-quality trials with larger sample sizes are needed to establish more specific protein intake guidelines for this population.