PhD defence A. (André) Mamede Soares Braga

Below is a brief summary of the dissertation: 

This dissertation explored why people did or did not engage in healthy behaviours, and how we could design better interventions to stimulate behaviour change. It examined the determinants of behaviour change and how intervention effects depended on both intervention characteristics and individual differences.

The first part identified factors linked to physical activity in adolescents, such as social support and perceived health. These patterns varied across gender and socioeconomic background, showing that interventions needed to be tailored rather than applied in the same way to everyone.

The second part reviewed interventions for adolescents from low income or minority backgrounds. Overall effects were small, but programmes that used several behaviour change techniques and reached young people across settings such as school, family and community appeared more promising.

A field experiment then tested a ten week workplace programme that used a gamified app and physical prompts to encourage walking. The app increased daily step counts, although the effect faded after the digital intervention was discontinued.

The final part examined the inner processes that shaped behaviour. One study showed that mindfulness supported mental health by improving emotion regulation and sleep. Another showed that people could use cognitive strategies to change food cravings in a way that encouraged healthier choices. These findings revealed that behaviour change depended not only on external tools but also on internal processes that helped people manage emotions and act in line with long term goals.

Together, the studies offered insights for creating more effective and lasting interventions for healthy behaviour.