Mechanisms of change within motivational interviewing in relation to health behaviors outcomes: A systematic review

• Systematic review: mechanisms of motivational interviewing and health behavior not addictions.
• Motivation and MI spirit appear to be the most promising mechanisms of MI.
• A potential causal chain, including therapist behavior and change talk was found.
• Mechanisms should be tested via mediation analysis to test the predictive validity.

ObjectiveMotivational interviewing (MI) has been identified as an effective treatment for health behaviors. Understanding the mechanisms of MI could have practical implications for MI delivery. This review is the first to examine mechanisms within MI that affect health behavior outcomes and summarizes and evaluates the evidence.MethodsA systematic literature search was conducted in PSYCHINFO, MEDLINE and EMBASE to identify studies that delivered individual MI in the context of health behaviors, excluding addictions, and investigated mechanisms of MI. Effect sizes were calculated.Results291 studies were identified and 37 met the inclusion criteria. Few of the 37 studies included, conducted mediation analyses. MI spirit and motivation were the most promising mechanisms of MI. Although self-efficacy was the most researched, it was not identified as a mechanism of MI. Study quality was generally poor.ConclusionAlthough this review has indicated possible mechanisms by which MI could influence health behavior outcomes, it also highlights that more high quality research is needed, looking at other possible mechanisms or causal pathways within health behavior outcomes.Practice implicationsMI spirit possibly plays an important role within MI and may potentially be used to evoke change talk which links to outcomes.