BACKGROUND Adipocytes were long considered inert components of the bone marrow niche, but mouse and human models suggest bone marrow adipose tissue (BMAT) is dynamic and responsive to hormonal and nutrient cues. METHODS In this study of healthy volunteers, we investigated how BMAT responds to acute nutrient changes, including analyses of endocrine determinants and paracrine factors from marrow aspirates. Study participants underwent a 10-day high-calorie protocol, followed by a 10-day fast. RESULTS We demonstrate (a) vertebral BMAT increased significantly during high-calorie feeding and fasting, suggesting BMAT may have different functions in states of caloric excess compared with caloric deprivation; (b) ghrelin, which decreased in response to high-calorie feeding and fasting, was inversely associated with changes in BMAT; and (c) in response to high-calorie feeding, resistin levels in the marrow sera, but not the circulation, rose significantly. In addition, TNF-α expression in marrow adipocytes increased with high-calorie feeding and decreased upon fasting. CONCLUSION High-calorie feeding, but not fasting, induces an immune response in bone marrow similar to what has been reported in peripheral adipose tissue. Understanding the immunomodulatory regulators in the marrow may provide further insight into the homeostatic function of this unique adipose tissue depot. FUNDING NIH grant R24 DK084970, Harvard Catalyst/The Harvard Clinical and Translational Science Center (National Center for Advancing Translational Sciences, NIH, award UL 1TR002541), and NIH grants P30 DK040561 and U19 AG060917S1.