Mitochondrial maladaptation and dysfunction contribute to the progression of metabolic dysfunction-associated steatohepatitis (MASH). Induction of Shc is implicated in progressive MASH during aging and the cytoplasmic p52Shc isoform in the activation of redox enzyme NOX2. The mitochondrial Shc isoform p46Shc represses acetyl-coenzyme A acyltransferase 2 (ACAA2) in vitro. ACAA2 is a key enzyme for lipid β-oxidation; however, the metabolic consequences of in vivo p46Shc induction are unknown. In the current study, p46Shc-inducible mice were generated; these and littermate controls were aged and fed chow or fast-food (high-fat and high-fructose) diet. p46Shc induction increased liver injury, inflammation, and lipid peroxidation. p46Shc overexpression did not significantly change liver triglycerides. On electron microscopy studies, mitochondria were swollen with aberrant cristae. p46Shc induction reduced mitochondrial oxygen consumption as measured by Oroboros, as well as suppressed the production of β-hydroxybutyrate, the central metabolite of therapeutic ketosis. Mitochondria exhibited increased production of reactive oxidative species. By contrast, the expression of dominant negative p46Shc reduced ACAA2 thiolase activity, improved β-oxidation, and reduced lipid peroxidation and production of reactive oxidative species. In summary, these studies support the concept that p46Shc induction in aging represses ACAA2, resulting in decreased mitochondrial β-oxidation and increased lipid peroxidation. Maintaining β-oxidation and ketogenesis could prevent liver injury, and targeting Shc-related maladaptive responses could be a successful therapeutic strategy in aging/MASH.