Purpose: A healthy diet is fundamental for healthy growth and for future disease prevention. However, scientific consensus on how to compose healthy diets for children has not been established. Therefore, a systematic review and meta-analysis was performed to investigate if an independent effect exists between foods, beverages or the composition of macronutrients and body composition in children and adolescents. 

Methods: A systematic search was performed in four databases up to July 2021. A systematic review of randomized controlled studies (RCTs) and meta-analyses were carried out by extracting mean difference (MDs) and standard deviation (SD) and performed using the random effect model. 

Results: Sixteen RCTs met inclusion criteria. Beyond dairy, sugar-sweetened beverages and macronutrient composition, no trials were identified for other food groups. Based on five RCTs (n:5), a higher-dairy diet was found to reduce body fat percentage − 0.47 [− 0.92, − 0.03] (p = 0.04). A higher-dairy diet was also found to increase lean body mass (kg) 0.34 [0.06, 0.62] (p = 0.02) (n:2), but did not affect BMI z-score − 0.05 [− 0.16, 0.06] (p = 0.39) (n:4). Substituting sugar-sweetened beverage with non-caloric beverages or flavored milk reduced body fat percentage (− 0.70 [− 0.78, − 0.62] (p < 0.001)) (n:3) but did not change BMI z-score (− 0.05 [− 0.20, 0.09] (p = 0.48)) (n:2). No significant effects were found between different macronutrient compositions and BMI z-score or body fat percentage. 

Conclusion: Changes in diet from low to higher-dairy consumption and from sugar-sweetened beverages to non-caloric beverages or flavored milk resulted in favorable changes in body composition among children and adolescents. Eligible studies investigating other foods are lacking. 

Trial registration: PROSPERO registration number (CRD42020173201).