Prolonged fasting increases the cholesterol efflux capacity and anti‐inflammatory functionality of HDL particles in human subjects.

Prolonged Fasting (>24hrs of 0 caloric intake; PF) has consistently been shown to be associated with a reduction in circulating levels of inflammatory cytokines and improvements in clinical parameters of immune disease in humans. These studies suggest a direct and potent link between PF and immune functionality however, the precise mediators and mechanisms underlying this link have remained largely unstudied. High density lipoprotein (HDL), though typically associated with its role in reverse cholesterol transport (RCT), has also been shown to be a potent regulator of multiple aspects of the human immune system and its composition and functionality is highly sensitive to nutritional interventions such as PF. Given this role in immune regulation and its nutritional sensitivity, HDL seems uniquely poised to play a role in exerting a portion of the beneficial effects associated with PF, however there have been no studies investigating the relationship between PF and HDL functionality. To address this knowledge gap, we have isolated the HDL of human subjects during various timepoints of a 48hr water only fast and tested these HDL for fasting induced alterations in their immunomodulatory and RCT functionalities. Based on these assessments we found that PF induces stark improvements in the functionality of HDL particles. PF increases the ability of HDL to promote cholesterol efflux from cholesterol‐loaded THP‐1 monocytes and increases the ability of HDL to suppress TNF‐α secretion from primary macrophage stimulated with pro‐inflammatory citrullinated‐fibrinogen immune complexes. Furthermore, increased fasting duration was directly associated with increased RCT ability and increased anti‐inflammatory capacity of HDL with the maximal effect being reached after 36hrs of fasting. To our knowledge, this is the first study to show that PF is capable of improving the RCT ability of HDL and modifying the immunomodulatory functionality of HDL towards a more anti‐inflammatory phenotype. These results thereby suggest that HDL may represent a novel mechanism by which PF exerts a portion of its systemic anti‐inflammatory and cardioprotective effects. Future studies of the influences of PF on HDL should focus on further assessing the full scope of the HDL functional alterations induced by PF and elucidating the compositional changes to HDL particles that underlie these functional effects.