Dietary fat quantity and composition influence hepatic lipid metabolism and metabolic disease risk in humans.

The excessive accumulation of intrahepatic triglyceride (IHTG) in the liver is a risk factor for metabolic diseases, including type 2 diabetes and cardiovascular disease. IHTG can excessively accumulate owing to imbalances in the delivery, synthesis, storage and disposal of fat to, in and from the liver. Although obesity is strongly associated with IHTG accumulation, emerging evidence suggests that the composition of dietary fat, in addition to its quantity, plays a role in mediating IHTG accumulation. Evidence from human cross-sectional and interventional studies indicates that diets enriched with saturated fat compared to other fat types and carbohydrates produce divergent effects on IHTG content. However, the mechanistic reasons for these observations remain unknown. Given the challenges of investigating such mechanisms in humans, cellular models are needed that can recapitulate human hepatocyte fatty acid metabolism. Here, we review what is known from human studies about how dietary fat, its quantity and composition contribute to IHTG accumulation. We also explore the effects of fatty acid composition on hepatocellular fat metabolism from data generated in cellular models to help explain the divergences observed in in vivo studies.