Changes in plasma cytokines following a 60-h fast are not influenced by the addition of exercise despite elevated ketones in healthy young adults

Immunometabolic processes maintain physiological homeostasis and are implicated in various chronic diseases. Fasting and exercise independently alter metabolic and immunological processes; their combination could provide insights into immunometabolic interactions. Using a randomized crossover design, 15 healthy adults (six females, nine males, 26.5 ± 4.3 years) fasted for 60 h with and without the addition of a 3 h cycling bout (65%–80% VO₂ peak). Fasting alone (FAST) and with exercise (FEX) reduced plasma glucose, insulin, respiratory exchange ratio, and increased β-hydroxybutyrate (BHB; all p < 0.01). FEX elicited more rapid changes in glucose and BHB and higher BHB concentrations at 60 h (all p < 0.01). Both conditions decreased circulating TNF-⍺ concentrations and increased IL-10 (p < 0.01), although the increase in IL-10 appeared to be driven by the FEX condition (p = 0.03). IL-6 concentrations tended to increase in both conditions (p = 0.1). Total white blood cell count remained unchanged after 60 h in both conditions, with only modest changes in some leukocyte subpopulations. Collectively, the observed changes in circulating cytokine concentrations support an overall anti-inflammatory effect of prolonged fasting, while the maintenance of leukocyte concentrations suggests immune function is not compromised. Despite greater metabolic strain, the addition of prolonged exercise did not appear to augment changes in systemic cytokines and leukocytes.