Health-compromising behaviours such as cigarette smoking and poor dietary habits are difficult to change. Most social-cognitive theories assume that the intention to change is the best predictor of actual change, but people often do not behave in accordance with their intentions. Unforeseen barriers emerge, or people give in to temptations. Therefore, intentions should be supplemented by more proximal predictors that might facilitate the translation of intentions into action.
Some self-regulatory mediators have been identified, such as perceived self-efficacy and strategic planning. They help to bridge the intention-behavior gap. The Health Action Process Approach (HAPA) suggests a distinction between (1) a preintentional motivation process that leads to a behavioural intention and (2) a postintentional volition process that facilitates the adoption and maintenance of health behaviours.
In this article, two studies are reported that examine mediators between intentions and two behaviours. One behaviour is smoking reduction in young adults, the other is dietary restraint in overweight patients with chronic disease. A structural equation model, specified in terms of the HAPA, was in line with both data sets but it explained more variance of dietary behaviours among middle-aged or older individuals with a health condition whereas variance of smoking reduction in healthy young adults was less well accounted for. The findings contribute to the elucidation of psychological mechanisms in health behaviour change and point to the particular role of mediator variables.