Food intake is often poor within the older population and many are at nutritional risk. Food intake is complex, as there are multiple individual, social, and environmental determinants that may interact and change over time. Social isolation has long been recognized as a key factor predicting nutrition risk in this population. However, the mechanisms by which social relationships influence diet among older adults remain poorly understood. The purpose of this review is two-fold: ( 1 ) to identify and, where possible, clarify the social concepts used in older adult nutrition research over the past two decades, specifically, the concepts of social integration, social support, companionship and commensality; and ( 2 ) to provide a review and summary of the empirical literature on social factors and diet among cognitively well older adults living in the community. Finally, challenges to studying social concepts in older adult nutrition and areas of future research will be discussed.