The human gut microbiome is significantly influenced by diet, which in turn affects host health, including immune function, nutrient metabolism, and the production of bioactive molecules. The gut microbiome is also closely linked to the development of mental disorders, highlighting the importance of dietary patterns in mental health. This review explores how different diets—such as the Western, Mediterranean, vegetarian, and ketogenic diets—impact the gut microbiome and their implications for neuropsychiatric and psychological disorders. Dietary patterns influence the gut microbiome composition and function through various mechanisms, including the production of short-chain fatty acids (SCFAs), cytokines, and neurotransmitters, which can affect brain function. The Western diet, characterized by high intake of refined sugars, saturated fats, and animal proteins, is associated with metabolic disorders and may alter the gut microbiome, leading to increased inflammation and a higher risk of mental disorders. In contrast, the Mediterranean diet, rich in fiber, unsaturated fatty acids, and antioxidants, is linked to improved cognitive function, reduced risk of depression, and better mental health outcomes. Vegetarian diets, which exclude animal products, have been associated with lower body fat, reduced risk of type 2 diabetes, and improved longevity. However, they may also lead to deficiencies in essential amino acids, which could affect mental health. The ketogenic diet, a high-fat, low-carbohydrate diet, has shown potential in reducing symptoms of epilepsy and other neurological disorders, though it may also alter the gut microbiome and affect mental health. The gut-brain axis, a bidirectional communication network, plays a crucial role in linking the gut microbiome to brain function. The composition and diversity of the gut microbiome are influenced by diet, and changes in the microbiome can affect mental health through the production of metabolites such as SCFAs and neurotransmitters. Future research should focus on understanding the complex interactions between diet, the gut microbiome, and mental health, and on developing targeted interventions such as probiotics and prebiotics to improve mental well-being. The integration of dietary interventions with other therapeutic approaches holds promise for the treatment of mental disorders.The human gut microbiome is significantly influenced by diet, which in turn affects host health, including immune function, nutrient metabolism, and the production of bioactive molecules. The gut microbiome is also closely linked to the development of mental disorders, highlighting the importance of dietary patterns in mental health. This review explores how different diets—such as the Western, Mediterranean, vegetarian, and ketogenic diets—impact the gut microbiome and their implications for neuropsychiatric and psychological disorders. Dietary patterns influence the gut microbiome composition and function through various mechanisms, including the production of short-chain fatty acids (SCFAs), cytokines, and neurotransmitters, which can affect brain function. The Western diet, characterized by high intake of refined sugars, saturated fats, and animal proteins, is associated with metabolic disorders and may alter the gut microbiome, leading to increased inflammation and a higher risk of mental disorders. In contrast, the Mediterranean diet, rich in fiber, unsaturated fatty acids, and antioxidants, is linked to improved cognitive function, reduced risk of depression, and better mental health outcomes. Vegetarian diets, which exclude animal products, have been associated with lower body fat, reduced risk of type 2 diabetes, and improved longevity. However, they may also lead to deficiencies in essential amino acids, which could affect mental health. The ketogenic diet, a high-fat, low-carbohydrate diet, has shown potential in reducing symptoms of epilepsy and other neurological disorders, though it may also alter the gut microbiome and affect mental health. The gut-brain axis, a bidirectional communication network, plays a crucial role in linking the gut microbiome to brain function. The composition and diversity of the gut microbiome are influenced by diet, and changes in the microbiome can affect mental health through the production of metabolites such as SCFAs and neurotransmitters. Future research should focus on understanding the complex interactions between diet, the gut microbiome, and mental health, and on developing targeted interventions such as probiotics and prebiotics to improve mental well-being. The integration of dietary interventions with other therapeutic approaches holds promise for the treatment of mental disorders.