Vegetarian and ketogenic diets: Their relationship with gut microbiome and mental health, and their clinical applications

In Western societies, vegetarian and ketogenic diets are increasingly raising attention. Understanding the differential effects of these dietary approaches could provide valuable insights into their potential clinical applications and, importantly, refine their use in targeted health promotion strategies. Therefore, the present narrative review examines the vegetarian and ketogenic diets, focusing on their association with the gut microbiome, their influence on mental health, and their potential clinical applications in healthcare settings. The vegetarian diet promotes gut microbiome diversity and enhances the growth of beneficial bacteria associated with fiber fermentation, supporting intestinal health and immune function. In contrast, the ketogenic diet induces ketosis and alters the gut microbiome by reducing certain beneficial bacteria but increasing others associated with metabolic shifts. In terms of mental health, vegetarian diets may improve psychological well-being and cognitive functioning, although there are contradictory results, while ketogenic diets have shown potential benefits in ameliorating seizure symptoms. Clinically, vegetarian diets are often recommended for preventing chronic diseases, managing cardiovascular conditions, and improving overall health, while ketogenic diets are primarily applied in epileptic patients but are also being tested for the treatment of various metabolic and mental disorders. Thus, both dietary approaches can offer potential clinical benefits, but understanding their impacts and underlying mechanisms is essential for developing dietary recommendations adapted to specific populations.