Effects of Varying Protein Amounts and Types on Diet-Induced Thermogenesis: A Systematic Review and Meta-Analysis

Protein is the most thermogenic macronutrient, but it is unclear how different amounts and types of protein impact diet-induced thermogenesis (DIT). The purpose of this meta-analysis was to compare the impact of isocaloric meals/diets containing different amounts or types of protein on energy metabolism. Databases were searched in June 2024 for studies that compare DIT or total daily energy expenditure (TDEE) in response to isocaloric acute meals or longer-term diets containing different amounts or types of protein. After identifying 3894 records, 52 studies were included. Standardized mean difference (SMD) estimates and 95% confidence intervals (CIs) were calculated for each outcome. In acute studies, intake of higher compared with lower-protein meals resulted in greater DIT (SMD: 0.45; 95% CI: 0.26, 0.65; P < 0.001) and TDEE (SMD: 0.52; 95% CI: 0.30, 0.73; P < 0.001). Notably, the subgroup analysis indicated that this effect on DIT was statistically significant for studies involving participants with normal weight but not overweight/obesity, although it is not clear if this finding was a true effect or because of study design characteristics. In chronic studies (ranging from 4 d to 1 y), intake of higher compared with lower-protein diets resulted in greater TDEE (SMD: 0.29; 95% CI: 0.10, 0.48; P = 0.003) and resting energy expenditure (SMD: 0.18; 95% CI: 0.01, 0.35; P = 0.039), but no differences in DIT (SMD: 0.10; 95% CI: -0.08, 0.28; P = 0.27). There was no evidence that different types of protein impacted energy metabolism. Higher protein meals/diets increase components of energy expenditure. This trial was registered at the International Prospective Register of Systematic Reviews (https://www.crd.york.ac.uk/prospero; PROSPERO 2023) as CRD42023389642.