The relationship of within-individual and between-individual variation in mental health with bodyweight: An exploratory longitudinal study.
PLoS ONE 2024 ; 19: e0295117.
Mueller J, Ahern AL, Jones RA, Sharp SJ, Davies A, Zuckerman A, Perry BI, Khandaker GM, Rolfe EL, Wareham NJ, Rennie KL
DOI : 10.1371/journal.pone.0295117
PubMed ID : 38198439
PMCID : PMC10781195
URL : https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0295117
Abstract
Poor mental health is associated with obesity, but existing studies are either cross-sectional or have long time periods between measurements of mental health and weight. It is, therefore, unclear how small fluctuations in mental wellbeing within individuals predict bodyweight over short time periods, e.g. within the next month. Studying this could identify modifiable determinants of weight changes and highlight opportunities for early intervention.
2,133 UK adults from a population-based cohort completed monthly mental health and weight measurements using a mobile app over a period of 6-9 months. We used random intercept regression models to examine longitudinal associations of depressive symptoms, anxiety symptoms and stress with subsequent weight. In sub-group analyses, we included interaction terms of mental health variables with baseline characteristics. Mental health variables were split into "between-individual" measurements (= the participant's median score across all timepoints) and "within-individual" measurements (at each timepoint, the difference between the participant's current score and their median).
Within-individual variation in depressive symptoms predicted subsequent weight (0.045kg per unit of depressive symptom severity, 95% CI 0.021-0.069). We found evidence of a moderation effect of baseline BMI on the association between within-individual fluctuation in depressive symptoms and subsequent weight: The association was only apparent in those with overweight/obesity, and it was stronger in those with obesity than those with overweight (BMI<25kg/m2: 0.011kg per unit of depressive symptom severity [95% CI -0.017 to 0.039]; BMI 25-29.9kg/m2: 0.052kg per unit of depressive symptom severity [95%CI 0.010-0.094kg]; BMI≥30kg/m2: 0.071kg per unit of depressive symptom severity [95%CI 0.013-0.129kg]). We found no evidence for other interactions, associations of stress and anxiety with weight, or for a reverse direction of association.
In this exploratory study, individuals with overweight or obesity were more vulnerable to weight gain following higher-than-usual (for that individual) depressive symptoms than individuals with a BMI<25kg/m2.
Lay Summary
Background: Research has suggested a connection between weight and mental health – with each potentially influencing the other – but the relationship is complex and remains poorly understood, particularly in relation to how changes in an individual’s mental health influence their bodyweight over time.
Methods: 2,133 adults living in the UK completed digital questionnaires on mental wellbeing and bodyweight every month for up to nine months during the COVID-19 pandemic (August 2020 – April 2021) using a mobile app. Questions assessed an individual’s symptoms of depression, anxiety and perceived stress. A higher score indicated greater severity. We then used statistical modelling to explore whether having poorer mental wellbeing than usual was related to changes in bodyweight one month later.
Results: We found a small association between having higher-than-usual depressive symptoms and weight gain. For every increment increase in an individual’s usual score for depressive symptoms, their subsequent weight one month later increased by 45g. This effect was only observed in those individuals with overweight (defined as BMI 25-29.9kg/m2) or with obesity (BMI of over 30kg/m2). Individuals with overweight had on average an increase of 52g for each increment point increase from their usual depressive symptoms score and for those with obesity the comparable weight gain was 71g. The effect was not seen in those individuals with a healthy weight. Although we found that having higher-than-usual symptoms of depression predicted higher weight, we found no link between generally having greater symptoms of depression and higher bodyweight. We found no evidence that weight predicted subsequent symptoms of depression. We also found no evidence that perceived stress or anxiety were related to changes in weight.
Conclusion: Overall, this suggests that individuals with overweight or obesity are more vulnerable to weight gain in response to feeling more depressed. Monitoring and addressing depressive symptoms in individuals with overweight or obesity could help prevent further weight gain and be beneficial to both their mental and physical health.