Given the interconnection between health and climate issues, shared predictors between behaviour and pro-environmental behaviour (PEB), and the risk of
crisis fatigue if attention is given to these issues one at a time, these should be targeted jointly. A change in multiple behaviours is needed to impact
planetary health, and multiple behaviour change programs are indeed generally more effective than single-behaviour programs in creating societal impact.
Insights are hence needed in which health behaviours and PEB can be targeted jointly. Multiple behaviour change is more successful when done sequentially than
simultaneously. However, sequential behaviour change raises the issue of transfer or spill-over, which happens when a first behaviour increases (positive) or
reduces (negative spill-over) the chance of adopting a next behaviour. Spill-over between health and pro-environmental behaviour has not yet been studied.
Crucially, a lack of insights in the mechanisms of multiple behaviour change is likely to result in ineffective interventions. 
This project aims to
assess how healthy lifestyle and pro-environmental behaviours in a general adult population can facilitate or conflict with each other. Finding health and
pro-environmental behaviours that facilitate each other will point to behaviours that can be targeted jointly, or where interventions are needed to reduce
conflict between these behaviours.