Residual symptoms are prevalent in major depressive disorder (MDD), encompassing a wide spectrum of symptoms such as sleep disturbances, changes in weight and appetite, cognitive impairment, and anxiety. These symptoms consistently impair daily functioning, diminish quality of life, and forecast disease relapse. Despite their clinical significance, residual symptoms lack a unified definition, potentially leading to confusion with treatment-emergent symptoms and ambiguity across studies, thereby hindering the generalizability of research findings. While some research identifies insomnia and mood disturbances as critical indicators, other studies emphasize different symptoms or find no significant correlation. Inconsistencies in defining residual symptoms, as well as methodological differences across studies, contribute to these conflicting results. While clinicians focus on alleviating negative symptoms to improve functional status, patients often prioritize achieving positive affect and overall well-being as essential components of successful treatment. It necessitates a comprehensive approach to patient care in depression. This review explores the phenomenon of residual symptoms in MDD, focusing on the ambiguity in definitions, clinical characteristics, and their impact on long-term outcomes. The lack of a standardized regulatory or academic definition for residual symptoms leads to varied interpretations among clinicians, underscoring the need for standardized terminology to guide effective treatment strategies and future research.

Major depressive disorder and bipolar disorder are the leading causes of global disability. Approximately 50% of patients fail to attain remission, prompting a pronounced focus on the significance of dietary patterns and specific nutrients within the pathophysiology of mood disorders. The connection between chronic diseases and mood disorders follows a bidirectional pattern: physical ailments are interrelated with affective disorders, and, concurrently, mood symptoms often precede chronic diseases and have the potential to worsen their prognosis. Nutraceuticals affect factors that could potentially impact the onset of mood disorders: monoamines and brain-derived neurotrophic factor (BDNF) concentrations, neuroinflammation, oxidative stress, and sleep quality. Furthermore, mood disorders rarely manifest in isolation. Typically, such patients concurrently experience other mental disorders or somatic comorbidities: obesity, hypertension, diabetes, polycystic ovary syndrome (PCOS), etc., where providing nutritional support is also pertinent. To optimize the therapeutic approach for individuals with mood disorders, incorporating nutritional support may not solely ameliorate symptoms stemming directly from the mental condition, but also indirectly through interventions targeting comorbidities.

This study evaluated the acute and short-term effects of repeated ketamine treatment on appetite in adult inpatients with treatment-resistant mood disorders, including major depressive disorder and bipolar disorder. Appetite, hunger, and desire to eat were assessed using the Visual Analog Scales (VAS) and the Simplified Nutritional Appetite Questionnaire (SNAQ) at baseline and at multiple time points up to 7 days following ketamine administration. No significant changes were observed over the course of treatment, and results were consistent across diagnostic groups and body mass index (BMI) categories. No increased risk of appetite-related undernutrition or clinically relevant weight loss was identified. These findings do not suggest a substantial short-term impact of ketamine on appetite regulation or body weight and are consistent with a favorable metabolic safety profile, supporting its clinical use in patients with treatment-resistant depression (TRD) and treatment-resistant bipolar disorder (TRBD).

Treatment-resistant depression (TRD) is associated with persistent symptoms, impaired functioning, physical comorbidity and a high risk of recurrence, making continuation and maintenance care particularly important. Nutrition may influence several modifiable aspects of recovery, including cardiometabolic health, daily functioning, self-care and treatment adherence, although evidence for a direct effect on depressive recurrence remains limited. This review examines the role of nutritional care within TRD relapse prevention, with particular attention to psychiatric nursing practise. Available dietary intervention studies in depression suggest potential benefits for depressive symptoms and broader health outcomes, but most have focused on acute treatment rather than recurrence or maintenance, and data specific to TRD remain sparse. Evidence for nurse-delivered nutritional interventions is also limited, although studies in broader psychiatric populations indicate that dietary assessment, education, behavioural support and follow-up can be incorporated into mental health care. In TRD, psychiatric nurses may contribute through nutritional risk screening, monitoring of appetite, intake, weight and physical health, reinforcement of agreed dietary recommendations, and coordination of specialist referral. Clear professional boundaries are required when malnutrition, eating disorders, refeeding risk, therapeutic diets or clinically significant nutrient–drug interactions are present. Nutritional care should therefore be regarded as an adjunct to established TRD treatment and integrated into multidisciplinary continuation and relapse-prevention care rather than used as a stand-alone intervention.