The gut-microbiome-brain axis plays a crucial role in the control of systemic metabolism and homeostasis. Recent research has shown that dietary habits and nutrients can affect immune system and inflammatory status by influencing various factors, including microbiome composition, microbial products release, gastrointestinal signaling molecules, and neurotransmitters. In addition, the gut microbiome affects the brain by altering levels of key brain transmitters, circulating cytokines, and short-chain fatty acids that can cross the blood-brain barrier. Immunonutrition, a newly born discipline, examines the relationship between diet, nutritional status, the immune system, inflammation, infection, injury, and healing. This review explores the relationship between nutrition and the immune system, focusing on immunonutrition and immunonutrients, the connections between nutrition, immunity, and the microbiome, microbiota-gut-brain communication, and potential nutritional interventions to improve neurological disorders. The manuscript provides a comprehensive overview of the complex interplay between nutrition and the immune system, highlighting the many ways in which our diets can impact our health and wellbeing, particularly in the context of neuroinflammatory and neurodegenerative conditions.