The relationship between weight, eating behaviours and mental health over time in the YOUTH longitudinal cohort study

Abstract Background Weight, eating behaviours and mental health have a complex interrelationship that is not fully understood. This study aimed to investigate the relationships between weight, eating behaviours and mental health over 12 months among socio-demographically diverse young adults (18–35 years) from the UK and Australia. Methods Longitudinal analysis of data from the YOUTH cohort study was conducted. Three timepoints of data were used (baseline, 6 months, 12 months), collected between 2021–2023 using online surveys hosted via the Prolific platform. The dataset includes 507, 371 and 336 participants at the respective timepoints. Random-intercept cross-lagged panel models (RI-CLPM) were used to explore the relationships between eating behaviours (addictive, disordered and emotional eating) and mental health (stress, depression, anxiety, quality of life) with weight (kilograms) over the three timepoints. Results Significant relationships were found between weight at baseline with Eating Disorder Examination Questionnaire (EDEQ) global score at 6 months ( β = 0.028, p = 0.005, 95% CI = 0.009, 0.048); Positive-Negative Emotional Eating Scale (PNEES)—positive score at 6 months ( β = −0.217, p = 0.011, 95% CI = −0.386, −0.053); and EDEQ shape concern score at 6 months ( β = 0.040, p < 0.001, 95% CI = 0.019, 0.060) and 12 months ( β = 0.034, SE = 0.010, p = 0.001, 95% CI = 0.014, 0.056). The relationships between EDEQ shape concern at baseline and weight at 12 months ( β = 1.845, p = 0.005, 95% CI = −0.017, 2.927), and weight at baseline with quality of life at 12 months ( β = −0.393, p = 0.034, 95% CI = −0.737, 0.031) were significant based on p value only. No other results were statistically significant for the other explanatory variables with weight. Conclusion Longitudinal relationships were identified for higher weight with higher disordered eating, less eating in response to positive emotions and lower quality of life in this young adult cohort. Future research should include more longitudinal analyses of these relationships. Findings also support the need for screening of disordered eating and mental ill-health in young adults within weight management services.