Large‐scale brain networks and neuroplastic processes support cognitive function across the lifespan and may be influenced by nutrition. This review integrates evidence from epidemiological studies, randomized dietary interventions, molecular neuroscience, and multimodal neuroimaging to examine the associations among dietary patterns, nutrient composition, brain network organization, and cognitive performance. Available evidence suggests that adherence to Mediterranean and MIND dietary patterns and a higher intake of omega‐3 fatty acids, polyphenols, and essential micronutrients are associated with better memory, executive function, and processing speed, whereas greater consumption of ultraprocessed foods is associated with cognitive decline. Nutrition may influence cognitive function through several interrelated mechanisms, including neurotrophic signaling, synaptic plasticity, neuroinflammation, cerebrovascular function, and gut–brain axis communication. Neuroimaging studies have also identified nutrition‐related differences in the organization and connectivity of large‐scale brain networks, including the default mode, central executive, and salience networks, some of which are associated with cognitive performance. However, the limited availability of longitudinal studies and well‐designed randomized controlled trials (RCTs) constrains causal inference. Emerging precision nutrition approaches that integrate metabolomics, microbiome profiling, genetic susceptibility, and network‐based neuroimaging may enable more targeted strategies to support cognitive health across the lifespan. Future research may prioritize large‐scale longitudinal studies, RCTs, and multimodal approaches integrating neuroimaging, metabolomics, and microbiome profiling to strengthen causal inference and advance precision nutrition strategies for cognitive health.