The overall objective of this study is to evaluate the effectiveness of an optimized lifestyle intervention based on dietary advice, behavioral support, and provision of key foods compared to dietary advice with behavioral support or dietary advice alone. The intervention aims to improve nutritional status, metabolic risk factors, and planetary sustainability. A total of 300 participants (150 men and 150 women) who meet all inclusion criteria and none of the exclusion criteria will be recruited. The study will be conducted at the Centre for Lifestyle Intervention at Östra Hospital in Gothenburg, led by researchers from Chalmers University of Technology, University of Gothenburg, and Sahlgrenska University Hospital. Participants will be recruited from two different socioeconomic areas in Gothenburg to examine how dietary interventions function in diverse population groups. The study follows a twelve-week randomized, controlled, parallel intervention design. Participants will be randomized into three groups, each with 100 individuals: Optimized lifestyle intervention group - receiving dietary advice, behavioral support, and provision of key foods. Behavioral support intervention group - receiving dietary advice and behavioral support. Control group - receiving dietary advice according to the SWITCH diet. The SWITCH diet, developed within the EU project SWITCH, is designed to align with European dietary guidelines and promote sustainable and healthy eating habits. It emphasizes whole grains, vegetables, fruits, legumes, and sustainable seafood while limiting processed foods, added sugars, and salt. Throughout the study, participants will undergo clinical assessments at baseline, midpoint (week 7), and endpoint (week 13). Key measurements include anthropometric data, blood pressure, blood glucose, blood lipids, and inflammatory markers. Dietary intake and sustainability aspects of food consumption will also be evaluated. Participants in the intervention groups will receive personalized coaching and access to practical resources, such as meal plans, recipes, and visual educational materials. The primary outcome of the study is the difference in cardiometabolic risk factors (e.g., blood lipids, blood pressure, glucose, insulin resistance markers) between the intervention groups. Secondary outcomes include changes in dietary intake, nutritional status markers, inflammatory markers, and sustainability measures (e.g., CO₂ emissions, land use, biodiversity impact). Additionally, exploratory analyses will investigate associations between diet, lifestyle changes, gut microbiota, and metabolic responses. This study aims to generate valuable insights into the effectiveness of different dietary intervention strategies in real-life Nordic conditions. The results will contribute to the development of evidence-based recommendations for sustainable and health-promoting dietary patterns.