Can metabolic fatty liver and hepatic insulin resistance raise ALT and worsen dysglycemia?

Metabolic dysfunction–associated steatotic liver disease (MASLD) and hepatic insulin resistance are closely linked metabolic abnormalities. The strongest evidence supports impaired insulin restraint of liver glucose output; ALT elevation is biologically credible but is a limited, nonspecific indicator.

Clinical and physiologic evidence

• Human tracer–hyperinsulinemic clamp studies show that NAFLD/MASLD is associated with deficient insulin-mediated suppression of endogenous hepatic glucose production. In one comparison, hepatic glucose production was suppressed by 63% of basal output in NAFLD versus 84% in controls (P=0.002).
• This is the clinically important defect: liver glucose output remains inappropriately high when insulin should suppress it, contributing directionally to hyperglycemia and broader dysglycemia.
• Basal fasting hepatic glucose production and fasting glucose can nevertheless be similar in nondiabetic steatosis and control groups. Thus, fatty liver does not necessarily mean continuously elevated fasting glucose production.

ALT and liver-injury interpretation

• Steatosis and hepatic insulin resistance plausibly contribute to ALT elevation through metabolic/lipotoxic hepatocellular injury. ALT correlates positively with a hepatic insulin-resistance index (r=0.25 in men; r=0.18 in women).
• ALT above roughly 30 U/L suggests chronic liver injury in the relevant setting; AASLD cites a true-normal range of approximately 29–33 U/L for men. However, normal ALT does not exclude MASLD, steatohepatitis, or advanced fibrosis, and ALT cannot stage disease.

Mechanistic explanation

• Intrahepatic diacylglycerol accumulation in metabolic fatty liver activates PKCε, impairing hepatic insulin-receptor signaling. This provides a coherent molecular route from steatosis to hepatic insulin resistance and failed suppression of glucose production.

Bottom line

• Metabolic fatty liver and hepatic insulin resistance can reinforce dysglycemia primarily by impairing insulin-mediated suppression of hepatic glucose production. They can plausibly raise ALT, but ALT alone neither diagnoses fatty liver nor reflects its severity; persistent elevation should prompt assessment of metabolic and alternative liver-injury causes, with fibrosis risk evaluated using FIB-4 and, when indicated, elastography or ELF.