Nonalcoholic fatty liver disease (NAFLD) affects up to one-third of the US population. Approximately one-fifth of patients with NAFLD have nonalcoholic steatohepatitis (NASH), characterized by hepatocyte damage and inflammation with or without fibrosis. NASH leads to greater risk of liver-related complications and liver-related mortality, with the poorest outcomes seen in patients with advanced fibrosis. NASH is also associated with other metabolic comorbidities and conveys an increased risk of adverse cardiovascular outcomes and extrahepatic cancers. Despite its high prevalence, NAFLD is frequently underdiagnosed. This is a significant concern, given that early diagnosis of NAFLD is a key step in preventing progression to NASH. In this review, we describe the clinical impact of NASH from the perspective of both the clinician and the patient. In addition, we provide practical guidance on the diagnosis and management of NASH for primary care providers, who play a pivotal role in the frontline care of patients with NASH, and we use case studies to illustrate real-world scenarios encountered in the primary care setting.

In Non-Alcoholic Fatty Liver Disease (NAFLD), events driving early hepatic dysfunction with respect to specific metabolic pathways are still poorly known.

We enrolled 84 subjects with obesity and/or type 2 diabetes (T2D). FibroScan® served to assess NAFLD by controlled attenuation parameter (CAP), and fibrosis by liver stiffness (LS). Patients with LS above 7 kPa were excluded. APRI and FIB-4 were used as additional serum biomarkers of fibrosis. The stable-isotope dynamic breath test was used to assess the hepatic efficiency of portal extraction (as DOB15) and microsomal metabolization (as cPDR30) of orally-administered (13C)-methacetin.

NAFLD occurred in 45%, 65.9%, and 91.3% of normal weight, overweight, and obese subjects, respectively. Biomarkers of liver fibrosis were comparable across subgroups, and LS was higher in obese, than in normal weight subjects. DOB15 was 23.2 ± 1.5‰ in normal weight subjects, tended to decrease in overweight (19.9 ± 1.0‰) and decreased significantly in obese subjects (16.9 ± 1.3, P = 0.008 vs. normal weight). Subjects with NAFLD had lower DOB15 (18.7 ± 0.9 vs. 22.1 ± 1.2, P = 0.03) but higher LS (4.7 ± 0.1 vs. 4.0 ± 0.2 kPa, P = 0.0003) than subjects without NAFLD, irrespective of fibrosis. DOB15 (but not cPDR30) decreased with increasing degree of NAFLD (R = -0.26; P = 0.01) and LS (R = -0.23, P = 0.03). Patients with T2D showed increased rate of NAFLD than those without T2D but similar LS, DOB15 and cPDR30.

Overweight, obesity and liver fat accumulation manifest with deranged portal extraction efficiency of methacetin into the steatotic hepatocyte. This functional alteration occurs early, and irrespective of significant fibrosis and presence of T2D.