Abstract
BACKGROUND: Depression remains a significant global health issue, yet the combined influence of dietary quality and extreme pessimistic thoughts on depressive risk is not fully understood. This study evaluated whether a Balanced Healthy Eating Index (BHEI) and extreme pessimism independently and jointly predict depression in adults. MATERIALS AND METHODS: We analyzed data from 17,575 participants aged 18-65 years in the 2007-2018 National Health and Nutrition Examination Survey (NHANES). BHEI scores above 62 were classified as meeting healthy dietary standards. Logistic regression models assessed the associations between substandard BHEI, extreme pessimism (frequent thoughts of being better off dead), and self-reported depression (PHQ-9 ≥ 10). Models were adjusted for age, sex, ethnicity, BMI, total energy intake, smoking status, alcohol use, and physical activity. RESULTS: Participants failing to meet the BHEI threshold had increased odds of depression (OR = 1.55, 95% CI: 1.37-1.76). Extreme pessimism further elevated depression risk (OR = 4.17, 95% CI: 3.40-4.41). An interaction effect showed that individuals with both substandard BHEI and extreme pessimism faced even higher odds of depression (OR = 8.05, 95% CI: 6.62-9.07), suggesting a multiplicative relationship. CONCLUSION: Both low-quality diets and extreme pessimistic thinking were significantly associated with depression risk, and the combination was particularly impactful. Future longitudinal studies are warranted to clarify causal pathways and to determine whether improving dietary patterns or mitigating extreme pessimism could reduce depression prevalence.