Distinct effects of ketogenic and non-ketogenic weight-loss diets on hepatic steatosis and mitochondrial metabolism in MASLD.

BACKGROUND & AIMS: Weight loss is the cornerstone of therapy for metabolic dysfunction-associated steatotic liver disease (MASLD). However, the optimal dietary approach for reducing intrahepatic triglycerides (IHTG) and the mechanisms underlying steatosis resolution remain poorly defined. We investigated whether weight loss via a ketogenic diet (KD) compared with a non-ketogenic diet (ND) differentially affects IHTG content, hepatic mitochondrial metabolism, and the circulating metabolome.

METHODS

Individuals with varying IHTG content underwent short-term hypocaloric KD and ND in a crossover design. Before and after each diet, IHTG was quantified by proton magnetic resonance spectroscopy and liver stiffness by magnetic resonance elastography. We used state-of-the-art isotope tracer methodology to compare in vivo rates of hepatic mitochondrial tricarboxylic acid (TCA) cycle oxidation, endogenous glucose production, and β-hydroxybutyrate production (ketogenesis). Targeted plasma metabolomics by NMR and LC-MS was used to evaluate systemic metabolic responses.

RESULTS

Despite similar energy deficits and body fat loss, IHTG decreased 45% more with KD than ND (-29% vs. -20%), accompanied by a threefold greater improvement in hepatic insulin sensitivity (59% vs. 21%). KD, but not ND, markedly reduced serum insulin concentrations (-54%), thereby promoting lipolysis and intrahepatic fatty acid partitioning toward mitochondrial β-oxidation, increasing hepatic mitochondrial [NADH]/[NAD+] (redox state) (+51%), and decreasing rates of hepatic mitochondrial TCA cycle oxidation (-34%). KD, but not ND, increased plasma concentrations of branched-chain amino acids, acylcarnitines, and TCA cycle intermediates.

CONCLUSIONS

Both diets ameliorated MASLD, but KD produced a greater reduction in IHTG owing to a starvation-like metabolic state. However, the benefits of KD were accompanied by increased hepatic mitochondrial redox state and suppression of TCA cycle oxidation, which are features previously linked to progressive liver injury.

IMPACT AND IMPLICATIONS: This study provides mechanistic justification for considering dietary composition, in addition to caloric restriction, as a key determinant of steatosis resolution in metabolic dysfunction-associated steatotic liver disease (MASLD). The findings highlight a potential trade-off between greater short-term reductions in liver fat and the emergence of metabolic features previously associated with increased susceptibility to liver injury. While a ketogenic diet may facilitate rapid liver fat reduction in selected clinical contexts, its use should be approached cautiously, particularly in individuals with advanced MASLD. These results underscore the need for systematic evaluation of dietary composition as a determinant of both efficacy and safety of nutritional interventions for MASLD.

CLINICAL TRIAL NUMBER: NCT03737071.