Association of dietary glycemic and insulin index/load with odds of major depressive disorder: a case-control study.

BACKGROUND: Dietary carbohydrate quality, reflected by glycemic index/load and insulin index/load, may influence brain function and mood through mechanisms such as glycemic fluctuations, oxidative stress, and inflammation. While several studies have assessed these indices in relation to depressive symptoms, their association with clinically diagnosed major depressive disorder (MDD) has not been investigated. We aimed to examine these associations in the present study. METHODS: This case-control study included 194 patients with MDD, diagnosed by a psychiatrist according to DSM-5 criteria, and 194 healthy individuals. Dietary information was collected using a validated food frequency questionnaire (FFQ). Dietary glycemic index (DGI), glycemic load (DGL), insulin index (DII), and insulin load (DIL) were calculated based on FFQ data. The severity of MDD was assessed using the Hamilton Depression Rating Scale (HDRS). Multivariable odds ratios (ORs) with 95% confidence intervals (CIs) were calculated. RESULTS: The odds of MDD was significantly higher in the third (T3) versus first tertile (T1) of DGI and DII (odds ratio: 1.73 (95% CI: 1.01-3.02) and 1.80 (95% CI: 1.03-3.12), respectively). However, there was no significant relation between DGL or DIL and MDD (third versus first tertile odds ratio: 1.43 (95% CI: 0.74-2.79) and 1.59 (95% CI: 0.66-3.83), respectively). CONCLUSIONS: Higher DGI and DII may be associated with increased odds of MDD, while DGL and DIL showed no significant associations. These findings highlight the importance of carbohydrate quality and insulin response in MDD, warranting further confirmation in large-scale prospective studies. CLINICAL TRIAL NUMBER: Not applicable.