Effectiveness and process evaluation of a mobile health weight gain prevention lifestyle program for young adults

Halting the rise in the prevalence of overweight is a priority for young adults, as the incidence of obesity is increasing among younger people. This thesis investigates the effectiveness and process evaluation of a randomised controlled trial weight gain prevention lifestyle mobile health program, called Text to Be Fit (TXT2BFiT), for young adults aged 18–35 years, including internal and external validity reporting to enable future translation. From 1,181 enquiries, 250 participants were randomised, costing AU$139 per person. At 12 weeks, the intervention group weighed significantly less, consumed more vegetables, fewer sugar-sweetened beverages (SSBs) and fewer energy-dense takeaway meals, consumed less total energy, total fat and saturated fat and increased total physical activity and total physical activity days compared to the controls. Intervention participants weighed less after nine months compared to control participants. No differences in physical activity were found, but all diet behaviours showed that intervention group had greater odds of improving their diet behaviours compared to controls. Participants reported high use of coaching calls, text messages and emails to help them achieve their goals. Website and app use and engagement was low. Males, mid-20s age group and higher income earners moderated intervention effects on weight changes at three months and males only at nine months. Mediating effects of diet and physical activity behaviour change explained 39% and 40% of the total effect on weight change at three and nine months respectively. Indirect effects of improved nutrition and physical activity behaviours at three and nine months in the intervention group were explained by changes in self-efficacy, explaining 8%–37% of the total effects. Standardised reporting of external validity components for weight gain prevention interventions among young adults is suggested to aid in strengthening the weight of evidence. In future, TXT2BFiT, could be translated for other populations of young adults using the findings from this thesis