Behavioural intention is a strong predictor of actual behaviour; however, many health interventions fail among individuals with a high intention to adopt healthy behaviours. This discrepancy, known as the intention-behaviour gap, remains a critical challenge in health promotion. The purpose of this study is to present a protocol designed to explore the predictability of perceptual factors that hinder the conversion of intention into weight loss behaviour among young adults.

This study employs a sequential explanatory mixed-methods design, comprising two distinct phases. In the first phase, a quantitative cross-sectional survey with a descriptive-analytical approach will be conducted to assess the frequency of behavioural intention to lose weight and weight loss behaviours. A multistage cluster sampling method will recruit young individuals aged 18–29 years with a body mass index of ≥25 kg/m² in Malekan County, Iran. Data will be collected using a structured questionnaire that includes sociodemographic information, physical activity measurements, a dietary adherence questionnaire and items assessing subjective norms, attitudes, perceived behavioural control and behavioural intention based on the Theory of Planned Behaviour. In the second phase, a qualitative study will be conducted using a purposive sampling strategy to select participants who can provide insights into the quantitative findings. Data collection in this phase will primarily involve in-depth individual interviews. A grounded theory approach will be used to develop a comprehensive understanding of the factors that impede the conversion of intention into behaviour among young individuals.

This protocol has been approved by the Ethics Committee of Tabriz University of Medical Sciences (IR.TBZMED.REC.1403.646). Written informed consent will be obtained from all participants. Findings will be disseminated through peer-reviewed publications, conference presentations and reports to relevant health authorities.