Motivation, accountability, and outcomes in a randomized controlled trial of internet weight-loss programs in primary...

This study explored whether baseline autonomous motivation (AM), controlled motivation (CM), and relative autonomy index (RAI) scores predicted 12-month weight in a three-arm randomized controlled trial of internet weight loss programs in primary care. It also evaluated perceived accountability to a primary care provider for weight loss as a moderator and study engagement (operationalized as weeks logged into the study website) as a mediator of these relationships. Participants with complete data for all model variables (n = 428) were included. Multiple linear regression models controlling for baseline weight and covariates showed that one-unit increases in baseline CM and RAI scores predicted a 0.57 kg increase (p = 0.015; Cohen's f² = 0.02) and 0.52 kg decrease (p = 0.019; Cohen's f² = 0.02) in weight, respectively. AM was not associated with 12-month weight. No moderating or mediating effects were found. Findings suggest the need for greater attention to baseline CM in weight loss programs in primary care.