Association between animal protein intake and overweight/obesity: A systematic review and meta-analysis of observational studies

Aims: To conduct a systematic review and meta-analysis of observational studies to investigate the association between Animal Protein Intake (API) and overweight/obesity across different age groups. Data synthesis: This review is registered in the International Prospective Register Of Systematic Reviews - PROSPERO database (CRD42023467451). Observational studies on the association between API and the outcome of overweight/obesity were included, up to September 2024, from ten databases. The risk of bias and study quality appraisal was assessed using the Agency for Health Care Research and Quality (AHRQ) tools for cross-sectional studies and the Newcastle-Ottawa Scale (NOS) for cohort studies. A systematic review and meta-analysis were performed with 14 and 11 studies, respectively, assessing individuals aged eight to 89 years, 55 % female. The meta-analysis indicated an increased likelihood of obesity with API in two cross-sectional studies (OR 1.18; 95 %CI 1.12–1.24; p < 0.001; I2: 0 %). Daily intake of animal protein ranging from 44.7 to 67.8 g/day (or 8.8 %–11.4 % of Kcal/day, on average) was associated with obesity. The risk of bias was considered low/moderate for most studies according to AHRQ, and four of the six cohort studies were rated as moderate quality by NOS. Conclusions: API appears to be associated with a higher likelihood of developing overweight/obesity, and increased Body Mass Index (BMI). Despite the multicausal nature of obesity, these findings suggest that reducing API may decrease the likelihood of overweight/obesity in the studied age groups.