Understanding how diabetes prevention programs (DPPs) achieve their effects remains uncertain. A systematic review published in the Journal of Diabetes Research evaluated potential mechanisms, mediators, and moderators influencing outcomes in psychosocial DPPs.

The review included 108 empirical studies involving 502,257 participants. Studies examining mechanisms, mediators, or moderators of intervention effects on health outcomes were selected, while qualitative, observational, and retracted studies were excluded. Five biomedical databases were searched from inception to November 2019. Study quality was assessed using the PEDro checklist, and outcome reporting bias was evaluated by comparing trial pre-registration records with published findings. A narrative synthesis was conducted due to heterogeneity across studies.

Across included studies, evidence supporting proposed mechanisms was limited. More studies failed to support than supported any mechanism, including weight-related factors. Approximately 30% of studies evaluated weight or adiposity-related mechanisms, and among these, 79% reported no support or indicated reduced effectiveness in individuals with higher weight. Due to limited supporting evidence, the predefined hypothesis could not be tested.

Findings indicate that mechanisms underlying DPP effects remain unclear. Mechanism testing was infrequently pre-registered, and a substantial proportion of studies were derived from a limited number of datasets.