SummaryA systematic review and meta‐analysis were conducted to assess the effectiveness of app‐based mobile interventions for improving nutrition behaviours and nutrition‐related health outcomes, including obesity indices (eg, body mass index [BMI]) and clinical parameters (eg, blood lipids). Seven databases were searched for studies published between 2006 and 2017. Forty‐one of 10 132 identified records were included, comprising 6348 participants and 373 outcomes with sample sizes ranging from 10 to 833, including 27 randomized controlled trials (RCTs). A beneficial effect of app‐based mobile interventions was identified for improving nutrition behaviours (g = 0.19; CI, 0.06‐0.32, P = .004) and nutrition‐related health outcomes (g = 0.23; CI, 0.11‐0.36, P < .001), including positive effects on obesity indices (g = 0.30; CI, 0.15‐0.45, P < .001), blood pressure (g = 0.21; CI, 0.01‐0.42, P = .043), and blood lipids (g = 0.15; CI, 0.03‐0.28, P = .018). Most interventions were composed of four behaviour change technique (BCT) clusters, namely, “goals/planning,” “feedback/monitoring,” “shaping knowledge,” and “social support.” Moderating effects including study design, type of app (commercial/research app), sample characteristics (clinical/non‐clinical sample), and intervention characteristics were not statistically significant. The inclusion of additional treatment components besides the app or the number or type of BCTs implemented did not moderate the observed effectiveness, which underscores the potential of app‐based mobile interventions for implementing effective and feasible interventions operating at scale for fighting the obesity epidemic in a broad spectrum of the population.