Effect of Oral Ketone Body Intake on Human CD8⁺ T-Cell Immunometabolism

Background/Objectives: The ketogenic diet (KD) has been shown to exert beneficial effects on human immunity by enhancing cytotoxic T lymphocyte function through metabolic reprogramming. However, strict dietary restrictions limit adherence and complicate its use in clinical practice. Exogenous ketone supplements have therefore been promoted as a more feasible alternative to elevate ketone body levels without the need for dietary changes. The objective of this study was to assess whether ketone salt or ketone ester supplementation can reproduce KD-mediated immunometabolic effects on CD8⁺ T cells in healthy individuals. Methods: In a prospective interventional study, healthy volunteers received either ketone salts (KS) or ketone esters (KE) for three weeks. Plasma β-hydroxybutyrate (BHB) concentrations were determined, and CD8⁺ T-cell cytokine secretion, functional responses, and mitochondrial energy metabolism were analyzed. In a subgroup, KS supplementation was combined with a carbohydrate-restricted, non-ketogenic diet. Results: While KS supplementation resulted in a short-lived increase in plasma BHB concentrations followed by increased BHB uptake in immune cells, KE supplementation led to more sustained plasma BHB levels, however, without detectable intracellular BHB accumulation. Neither intervention affected CD8⁺ T-cell cytokine production, functional capacity, or mitochondrial energy metabolism, and KS intake combined with a carbohydrate-restricted, non-ketogenic diet likewise did not alter CD8⁺ T-cell immunometabolic parameters. Conclusions: Transient elevation of circulating ketone body levels through supplementation seems insufficient to reproduce the immunometabolic effects of a KD, which likely require broader metabolic adaptations. Thus, the impact of exogenous ketones on adaptive immunity in healthy individuals appears limited.