Effect of early-life protein supplementation on childhood obesity and related metabolic outcomes: a systematic review and meta-analysis.

Abstract

Protein intake during complementary feeding plays a vital role in childhood growth. However, the effects of varying protein quantity and source on obesity and related metabolic outcomes remain uncertain. This study aimed to evaluate the effect of protein intake (quantity and source) on childhood obesity [weight-for-length Z-score (WLZ) > 2], body composition [fat mass (FM), fat-free mass (FFM)], and metabolic markers (insulin, insulin-like growth factor-1) in children aged 6-23 mo, including outcomes beyond 24 mo where available. A systematic search was conducted in MEDLINE, Cochrane CENTRAL, Embase, Web of Science, and CINAHL (January 2000-May 2024) for randomized controlled trials that compared high with low protein intake (diets with higher protein defined as an absolute difference of ≥5 g/d between groups), animal compared with plant-based protein, and meat compared with dairy. Random-effects meta-analyses were performed, and heterogeneity was assessed using I 2 statistics. Owing to the lack of binary obesity outcome data, WLZ was analyzed as a continuous measure to assess shifts in weight-for-length distribution. Of 5817 records identified, 20 publications (from 19 trials) met the inclusion criteria, with 12 included in the meta-analysis. Diets with higher protein content did not substantially affect WLZ. Standardized mean difference (SMD) was 0.0 (95% CI: -0.09, 0.09) for low- and middle-income countries and 0.17 (95% CI: -0.12, 0.47) for high-income countries. No effects were found for FFM [SMD: -0.05 (95% CI: -0.31, 0.21)] or FM [SMD: 0.17 (95% CI: -0.41, 0.74)]. We were not able to identify any effects of protein source of any of the outcomes. Insufficient data precluded meta-analysis for metabolic markers. There is limited evidence of any impact of protein quantity or quality during complementary feeding on growth or body composition. Given the short-lasting exposures and follow-up times, the long-term metabolic effects of protein supplementation require further investigation. This trial was registered at PROSPERO as CRD42024550409.