Sex-Specific Metabolic Footprint of Ketogenic Diet in C57BL/6J Mice

<b>Background/Objectives</b>: The ketogenic diet (KD) induces profound metabolic shifts, yet the sex-specific long-term effects on skeletal muscle metabolism and sterol homeostasis across tissues remain insufficiently characterized. This study tested the hypothesis that a prolonged KD would elicit distinct, sex-dependent metabolic and sterol adaptations in mice. <b>Methods</b>: We examined how a 12-week KD, compared with a standard diet, affected body mass, the skeletal muscle metabolome, hepatic lipid and collagen content, and sterol profiles in the skeletal muscle, liver, spleen, and serum in male and female C57BL/6J mice. Three-month-old mice of both sexes were randomized to a KD or standard diet and evaluated using the histological quantification of hepatic steatosis and collagen deposition, matrix-assisted laser desorption/ionization time-of-flight imaging mass spectrometry (MALDI-TOF IMS) of skeletal muscle, and LC-MS/MS-based sterol profiling. <b>Results</b>: The KD induced rapid body mass gain in males and delayed weight gain in females, promoted hepatic steatosis in both sexes, and generated clearly segregated, sex- and diet-specific skeletal muscle metabolomic signatures. These signatures included reduced tricarboxylic acid cycle precursors and a marked decrease in S-adenosylmethionine in KD-fed females. Across tissues, the KD consistently suppressed precursor sterols, including 7-dehydrocholesterol and desmosterol in the skeletal muscle, liver, and spleen, while elevating serum cholesterol and desmosterol (male-biased), with changes generally more pronounced in males. <b>Conclusions</b>: Collectively, these findings demonstrate that a long-term KD drives sex- and organ-specific metabolic remodeling, with evidence of greater metabolic flexibility but a shared risk of hepatic steatosis in females. These results underscore the importance of personalized, sex-stratified approaches when considering long-term ketogenic interventions.