1 Faculty of Land and Food Systems, Food, Nutrition and Health, the University of British Columbia, Vancouver, Canada.
2 Healthy Starts, British Columbia Children's Hospital Research Institute, Vancouver, Canada.
3 School of Exercise Science, Physical & Health Education, University of Victoria, Victoria, Canada.
4 PERFORM Research Centre, Concordia University, Montreal, Canada.
5 School of Human Nutrition, McGill University, Montreal, Canada.
6 Faculty of Land and Food Systems, Food, Nutrition and Health, the University of British Columbia, Vancouver, Canada. tamara.cohen@ubc.ca.
7 Healthy Starts, British Columbia Children's Hospital Research Institute, Vancouver, Canada. tamara.cohen@ubc.ca.
8 PERFORM Research Centre, Concordia University, Montreal, Canada. tamara.cohen@ubc.ca.

Background: Consuming a balanced diet and regular activity have health benefits. However, many adults have a difficult time adhering to diet and activity recommendations, especially in lifestyle interventions. Adherence to recommendations could be improved if common facilitators and barriers are accounted for in intervention design. The aim of this systematic review was to understand perceived barriers and facilitators to lifestyle (diet and/or activity) intervention guidelines.

Methods: This review follows the Preferred Reporting Items for Systematic Reviews and Meta-Analysis guidelines. Studies included relied on qualitative methods to explore the barriers and facilitators healthy adults ([Formula: see text] 18 years) experienced in lifestyle interventions. Google Scholar, Cochrane Reviews, Medline, PubMed, and Web of Science were searched from January 2005 to October 2021. Main themes from each paper were thematically analyzed and reported as a barrier or facilitator to adherence at the individual, environment or intervention level using inductively derived themes. Study quality was assessed using the Critical Appraisal Skills Programme.

Results: Thirty-five papers were included. Of these, 46% were conducted in North America and the majority had more female participants (86% in mixed-sex studies, 26% females only). Similar themes emerged across all three levels as facilitators and barriers. At the individual level, attitudes, concern for health and physical changes. At the environmental level, social support, social accountability, changeable and unchangeable aspects of the community. Finally, delivery and design and content at the intervention level. An additional facilitator at the intervention level included fostering self-regulation through Behavior Change Taxonomies (BCT).

Conclusions: Lifestyle interventions that foster self-regulatory skills, opportunities for social engagement and personalization of goals may improve behaviour adherence. This can be achieved through inclusion of BCT, tapering off of intervention supports, identification of meaningful goals and anticipated barriers with participants.