BACKGROUND: An increase in intrahepatic triglyceride (IHTG) is the hallmark feature of nonalcoholic fatty liver disease (NAFLD) and is decreased by weight loss. Hepatic de novo lipogenesis (DNL) contributes to steatosis in people with NAFLD. The physiological factors that stimulate hepatic DNL and the effect of weight loss on hepatic DNL are not clear.
METHODS: Hepatic DNL, 24-h integrated plasma insulin and glucose concentrations, and both liver and whole-body insulin sensitivity were determined in people who were lean (n = 14), obese with normal IHTG content (Obese, n = 26) and obese with NAFLD (Obese-NAFLD, n = 27). Hepatic DNL was assessed by using the deuterated water method corrected for the potential confounding contribution of adipose tissue DNL. Liver and whole-body insulin sensitivity were assessed by using the hyperinsulinemic-euglycemic clamp procedure in conjunction with glucose tracer infusion. Six subjects in the Obese-NAFLD group were also evaluated before and after 10% diet-induced weight loss.
RESULTS: The contribution of hepatic DNL to IHTG-palmitate was 11%, 19% and 38% in the Lean, Obese and Obese-NAFLDgroups, respectively. Hepatic DNL was inversely correlated with hepatic and whole-body insulin sensitivity, but directly correlated with 24-h plasma glucose and insulin concentrations. Weight loss decreased IHTG content, in conjunction with a decrease in hepatic DNL and 24-h plasma glucose and insulin concentrations.
CONCLUSIONS: These data suggest hepatic DNL is an important regulator of IHTG content, and that increases in circulating glucose and insulin stimulate hepatic DNL in people with NAFLD. Weight loss decreases IHTG content, at least in part, by decreasing hepatic DNL.