In a new study published in PLOS One, researchers found a subtle yet significant relationship between changes in individual levels of depressive symptoms and subsequent weight gain. Conducted on over 2,000 participants, this study provides evidence that even minor deviations from one’s typical depressive symptoms can influence body weight, particularly among those with higher body mass index (BMI).
For years, scientists have known that there’s a complex, two-way street between mental health and weight. People who struggle with their weight often face mental health challenges, and vice versa. However, this relationship has remained somewhat of a mystery, with most studies offering only cross-sectional snapshots of how mental health relates to weight at specific points in time.
The need for a clearer understanding of this interaction, especially how mental health changes within an individual affect their weight over time, has been a significant gap in research. This understanding is crucial, as it could help in developing strategies to prevent weight gain, particularly in the context of mental health.
“We were interested in this topic because obesity – and helping people to maintain a healthy weight – remain critical public health challenges. Currently, two-thirds of adults in England are living with overweight or obesity,” explained study author Julia Mueller from the MRC Epidemiology Unit at the University of Cambridge.
“Overweight and obesity increase the risk for numerous health problems, including diabetes, cardiovascular disease and cancers. 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. A better understanding of the relationship between mental wellbeing and weight changes can help us understand how we can provide more effective psychological support for people trying to lose weight.”
For their study, the researchers used data from a segment of the Fenland Study, a comprehensive health study of over 12,000 people in the United Kingdom. The Fenland COVID-19 study, a sub-study conducted during the pandemic, provided a unique opportunity to investigate these changes due to the expected higher fluctuations in weight and mental health during this period.
A total of 2,133 participants, aged 44 to 70 years, were included in the analysis. They provided data on their mental health and weight via a mobile app over 6-9 months. Mental health was assessed using three validated questionnaires: the Patient Health Questionnaire for depressive symptoms, the Generalised Anxiety Disorder questionnaire for anxiety symptoms, and the Perceived Stress Scale for perceived stress. Body weight was the primary outcome, with participants reporting their weight monthly.
The researchers found no significant association between within-individual variations in anxiety symptoms or stress and subsequent body weight. However, a notable connection was observed with depressive symptoms. The data showed that when individuals experienced a rise in depressive symptoms from their usual level, it was associated with a slight increase in body weight in the following month.
“We found that even small changes in symptoms of depression are predictive of increases in weight, regardless of whether people meet definitions for ‘clinical depression’ or not,” Mueller told PsyPost.
This effect was primarily observed in participants with higher body mass indexes. This suggests that those who are already overweight or obese might be more susceptible to weight changes in response to mood alterations.
“We found that increases in symptoms of depression are associated with a subsequent increase in body weight when measured one month later,” Mueller explained. “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). The effect was not seen in those individuals with a BMI below 25kg/m2. Overall, our findings suggest that individuals with overweight or obesity are more vulnerable to weight gain in response to feeling more depressed.”
The researchers discovered that each unit increase in a person’s typical depressive symptoms score was associated with a weight gain of 45 grams in the following month. For instance, if an individual’s score for depressive symptoms increased from five to 10, signifying a shift from mild to moderate depressive symptoms, this change would correspond to an average weight gain of about 225 grams (0.225 kg). While this amount might appear minor, it can accumulate significantly over time.
“Although the weight gain was relatively small, even small weight changes occurring over short periods of time can lead to larger weight changes in the long-term, particularly among those with overweight and obesity,” Mueller told PsyPost. “People with a high BMI are already at greater risk from other health conditions, so this could potentially lead to a further deterioration in their health. Monitoring and addressing depressive in individuals with overweight or obesity symptoms (even if criteria for clinical diagnoses of depression are not met) could help prevent further weight gain and be beneficial to both their mental and physical health.”
A further surprising revelation was the lack of a reciprocal relationship. The study found no evidence to suggest that changes in body weight could predict future changes in mental health. This finding challenges the often-held belief that the relationship between mental health and body weight is always bidirectional.
“Apps on our phones make it possible for people to answer short questions at home more frequently and over extended periods of time, which provides much more information about their wellbeing,” added senior author Kirsten Rennie. “This technology could help us understand how changes in mental health influence behaviour among people with overweight or obesity and offer ways to develop timely interventions when needed.”
However, the study’s insights come with certain limitations. The reliance on self-reported weight measurements could introduce some bias, as individuals might over- or under-report their weight. Moreover, the study’s observational nature means that while it can highlight correlations, it cannot firmly establish causation.
“This study is an exploratory, observational study, so we can’t draw firm conclusions about whether changes in symptoms of depression cause weight changes,” Mueller said. “Future research could more closely examine how changes in mental wellbeing influence behaviours like diet and physical activity.”
The study, “The relationship of within-individual and between-1 individual variation in mental health with bodyweight: An exploratory longitudinal study“, was authored by Julia Mueller, Amy L. Ahern, Rebecca A. Jones, Stephen J. Sharp, Alan Davies, Arabella Zuckerman, Benjamin I. Perry, Golam M. Khandaker, Emanuella De Lucia Rolfe, Nick J. Wareham, and Kirsten L. Rennie.
