Comparison of Habitual Protein Intake and Protein Metabolism Between Asian and Western Countries. A Systematic Review...

Differences in habitual protein intake amount and source between Asian and Western countries may influence protein metabolism outcomes.

Dietary protein and amino acid intake were compared, and how higher protein intake affected protein metabolism outcomes, specifically nitrogen balance and amino acid concentrations, was compared between Asian and Western countries.

Systematic searches were conducted in the CINAHL, Cochrane, Embase, and PubMed (inception to February 1, 2023) databases, filtered by English language, for articles on studies conducted with human adult participants (≥19 years old).

Observational studies and clinical trials reporting habitual protein or amino acid intake, and clinical trials investigating varying protein amounts on nitrogen balance or blood amino acid concentrations were included. Two independent reviewers extracted study characteristics.

Data were synthesized using random effects meta-analyses following Preferred Reporting Items for Systematic Reviews and Meta-Analyses and Meta-analysis of Observational Studies in Epidemiology guidelines. Quality assessment was performed using MMAT, version 2018. Key outcomes included country-specific total protein intake from animal and plant protein sources; differences in protein amount and source, and resulting amino acid intakes between Asian and Western countries, with subgroup analyses by sex, age, body mass index, and population; and effects of higher protein intake on nitrogen balance and fasting or postprandial blood amino acid concentrations.

Of 1787 articles included, 1649 reported habitual protein or amino acid intake, and 168 reported protein metabolism outcomes. As a whole, populations in Western countries consumed more total protein (16.4% of total energy intake [E%] vs 14.7 E%), animal protein (10.6 E% vs 7.0 E%), and less plant protein (5.9 E% vs 7.4 E%) than those in Asian countries. Male individuals generally consumed more protein, particularly from animal and plant sources in Western countries, and from plant sources in Asian countries. Higher protein intake caused a significantly more positive nitrogen balance in Western countries (0.86 to 1.21 g) than Asian countries (-0.31 to 0.23 g), suggesting potential differences in postprandial nitrogen balance regulation and protein utilization. However, caution is advised, given the limited studies in Asian countries. Additionally, the importance of considering differences in units (ie, absolute vs body weight adjusted) when reporting protein intake and its effects on protein metabolism should be considered.

Populations of Asian and Western countries differed in protein intake amounts, sources, and metabolism.

PROSPERO registration no. CRD42024612020.