Solitary eating is linked to reduced brain volume in cognitively unimpaired individuals and possible future cognitive decline.

Social isolation and poor nutrition are recognized risk factors for cognitive decline in older adults. However, the relationship between solitary eating, brain structure, and dietary patterns remains unclear. This study investigated the relationship between solitary eating, brain structure, and diet in healthy older Japanese adults. A total of 727 cognitively normal participants (mean age 70.32 years) underwent MRI and dietary assessments. Results showed that individuals who frequently eat alone have reduced brain volumes in regions critical for cognitive function, particularly the medial temporal lobe and hippocampus. These individuals also demonstrated less healthy dietary patterns, characterized by higher sugar and alcohol consumption, with lower intake of proteins, vitamins, and minerals. Analysis revealed that the difference in hippocampal volume between solitary and social eaters diminished when accounting for dietary factors, suggesting that nutritional factors primarily drive this relationship. However, the difference in medial temporal lobe volume remained significant after dietary adjustment, indicating that other factors, such as reduced social interaction, may affect this region. These findings emphasize the importance of social eating for maintaining brain health in older adults, suggesting that both social and nutritional aspects of eating are crucial. This research provides insights for developing healthy aging strategies that address both social and nutritional dimensions of eating behavior.