Association Between Change in Body Mass Index and Depression Severity During a Three-Month Dietary Intervention: A Quasi-Experimental Study

Background Obesity and depression are increasingly prevalent public health concerns that frequently coexist and may exacerbate each other. Evidence suggests that weight loss through dietary modification can improve mental health outcomes, yet data from low- and middle-income countries remain limited. Objective To evaluate the association between changes in body mass index (BMI) and depression severity following a three-month dietary intervention among adults in Pakistan. Methods A quasi-experimental study was conducted at the Department of Community Medicine and Telemedicine Nutrition Counter, King Edward Medical University, Lahore. Participants received individualized counseling and a calorie-restricted diet plan (approximately 1600 kcal/day). BMI and depression severity, measured using the Hamilton Depression Rating Scale (HAM-D), were recorded at baseline and after three months. Statistical analyses included paired t-tests, Pearson correlation, and linear regression. Results A total of 277 adults (25.6 \(\:\pm\:\)5.9 years; 50.2% male) were enrolled through convenience sampling. Mean (SD) BMI decreased from 31.96 (3.80) kg/m² to 30.16 (4.20) kg/m² (mean change, − 1.80 kg/m²; P < .001). HAM-D scores improved from 14.05 (4.55) to 10.51 (4.00) (P < .001). Post-intervention, 23.1% of participants achieved normal depression scores. Change in BMI significantly predicted improvement in depression severity (β = 0.493; P < .001). A strong positive correlation was found between BMI and depression score changes (r = 0.646; R² = 0.42). Conclusion Weight reduction achieved through dietary intervention was significantly associated with improvement in depressive symptoms among obese adults. These findings emphasize the need for integrated nutritional and psychological approaches to address the dual burden of obesity and depression in developing settings.