Obesity and Depression.

Obesity and depression are common chronic conditions that have profound impacts on physical and mental health worldwide. Epidemiological studies increasingly demonstrate that these disorders frequently co-occur, and their comorbidity amplifies the risk of other chronic diseases. This comorbidity has a potential bidirectional relationship, and various psychological, sociodemographic, and lifestyle factors contribute to the association between obesity and depression. The first part examines how each condition may act as a risk factor for the other and explores methodological issues in existing research, such as differences in study populations and measurements of obesity. Both conditions share symptoms such as depressed mood, fatigue, diminished energy, changes in appetite and weight, and low self-confidence and self-esteem. In particular, we focus on how fatigue and changes in appetite develop and manifest in each condition.The second part reviews the psychological factors and biological mechanisms underlying the conditions. From a psychological perspective, we explore how general psychopathology, personality traits, body image concerns, and clinical implications related to obesity can contribute to depression, supported by a case example. We also highlight how psychosocial factors associated with depression can lead to weight gain by reinforcing a cycle of low mood and unhealthy eating patterns. From a biological aspect, we review recent findings on hypothalamic-pituitary-adrenal axis dysregulation, chronic inflammation, altered adipokine activity, insulin resistance, and oxidative stress. These insights underscore how metabolic disturbances may influence mood regulation and vice versa.