Combined Effects of Physical Activity and Obesity on Cognitive Function: Independent, Overlapping, Moderator, and Mediator Models

This article reviews studies on physical activity, obesity, and cognition to explore how physical activity and obesity may work independently or together in affecting cognitive function. In particular, we propose six hypotheses derived from four conceptual models to advance our understanding of the combined effects of physical activity and obesity on cognition. The four conceptual models are distinguished by the presumed temporal relationship and the presumed correlation between physical activity and obesity and include an independent model, an overlapping model, a moderator model, and a mediator model. Among the 16 studies testing the effects of physical activity and obesity on cognition in a combined approach, the moderator model, viewing either physical activity or obesity as the potential moderator, was most frequently examined (n = 10), mediator (n = 3) and independent (n = 2) models received relatively less attention, and only a single study used an overlapping model. Results were mixed when considering the moderator, independent, and mediator models. The single study that took an overlapping model approach found support for the model hypothesis. One relevant observation from this review is that the variance within the small extant literature with respect to the choice of conceptual model limits our ability to make assertive conclusions relative to the relations among the examined variables. Given the logic supporting a combined effect of physical activity and obesity on cognition, researchers are encouraged to consider the possible models of the relationship as they design studies to further address this research question.