Effect of low-carbohydrate diet on depression and anxiety: A systematic review and meta-analysis of controlled trials

Background: Despite considerable advances in pharmacological and non-pharmacological treatments, mental health illnesses carry many economic and social burdens. Depression and anxiety are known as mental disorders which are highly prevalent worldwide. Previous studies have shown different results. This diet has attracted enormous interest. Objective: This is the first meta-analysis conducted to review systematically all trials to evaluating the effect of a low carbohydrate diet (LCD) on depression, and anxiety. Methods: PubMed, Web of Science, and Scopus have been searched until 9 September 2021. In total, 8 RCTs (n = 590) were carried out for evaluation the effects of LCDs on depression and anxiety were included. All the trials included in the analyses evaluated patients without a mood disorder. Random model effects meta-analysis was conducted. To evaluate the heterogeneity among the included studies. The egger test was used. Subgroup analyses performed based on regions, assessment methods, carbohydrate intake and duration of studies. Results: This study did not show any significant association between a low carbohydrate diet and the of anxiety (SMD = 0.19, 95 % CI -0.10, 0.47; P = 0.20) and also depression (SMD = 0.06, 95 % CI -0.11, 0.24; P = 0.49). If one of the studies is excluded, this diet significantly increases anxiety (SMD = 0.33, 95 % CI 0.12, 0.54; P < 0.001). This study showed that this diet increases anxiety in studies with <26 % carbohydrate intake (SMD = 0.31; 95%CI 0.10, 0.52; P < 0.001; I2 = 0.00, P = 0.52), in the Australia (SMD = 0.29; 95%CI 0.08, 0.49; P = 0.01; I2 = 0.00, P = 0.42), and in studies that used the Spielberger State Anxiety Inventory (SAI) to assess anxiety (SMD = 0.33; 95%CI 0.11, 0.54; P < 0.001; I2 = 0.00, P = 0.54). Limitations: One of the limitations of intervention studies examining the effect of diet is that it is difficult to blind people under intervention. Conclusion: The present study did not demonstrate significant association between a low carbohydrate diet and improvement of depression and anxiety. More accurate studies are needed to reach definitive conclusions.