Ketone body supplementation in keto-adapted mice reveals metabolic adaptations and glycogen-independent exercise capacity.

Ketone body supplementation has gained attention for its metabolic effects, but its impact on exercise metabolism remains controversial. We hypothesized that the metabolic response to ketone supplementation differs between keto-adapted and keto-naïve states. In this study, we investigated the effects of β-hydroxybutyrate (BHB) supplementation in keto-adapted mice. Mice were assigned to three groups: control diet (CON), ketogenic diet (KD), or KD with sodium β-hydroxybutyrate supplementation (KD+BHB) for 6 weeks. Chronic BHB supplementation in keto-adapted mice (KD+BHB) further elevated circulating ketone levels compared to KD alone (2.63 ± 0.53 vs. 1.96 ± 0.34 mM, p < 0.05). Despite significantly lower muscle glycogen content, both KD and KD+BHB groups maintained exercise capacity comparable to controls, demonstrating a glycogen-thrifty effect. During exercise, both KD groups showed greater BHB utilization and glucose preservation compared to controls. Gene expression analysis revealed upregulation of fatty acid oxidation-related genes across multiple tissues in KD+BHB mice, with more pronounced effects than KD alone. Additionally, KD+BHB mice showed increased AMPK phosphorylation (p < 0.05 vs. CON) and reduced mTOR activation (p = 0.058 vs. CON) in liver and skeletal muscle, creating a metabolic environment favoring fat utilization. These findings demonstrate that ketone supplementation in keto-adapted status creates a glycogen-thrifty state during exercise, suggesting metabolic context significantly influences responses to exogenous ketones.