Non-alcoholic fatty liver disease (NAFLD) has a well-known association with obesity; however, the condition is increasingly being identified in non-obese individuals as well.

Therefore, the present systematic review and meta-analysis sought to determine the prevalence, incidence, and long-term outcomes of non-obese or lean NAFLD at a global level.

Investigators searched PubMed, Embase, Scopus, and the Cochrane Library from inception to May 1, 2019, for relevant original research articles without a language barrier. Primary outcomes included prevalence of non-obese or lean people within the NAFLD group and the prevalence of non-obese or lean NAFLD in the general, non-obese, and lean populations; the incidence of NAFLD among non-obese and lean populations; and long-term outcomes of non-obese people with NAFLD. Investigators also determined the demographic, clinical, and histological characteristics of individuals with non-obese NAFLD.

In all, 93 studies involving 10 576 383 subjects from 24 countries or areas were identified: 84 studies (n=10 530 308) were used for the prevalence analysis, five (n=9121) were used for the incidence analysis, and eight (n=36 954) for the outcomes analysis.

Within the NAFLD population, 19.2% of the individuals were lean and 40.8% (36.6-45.1) were non-obese. The prevalence of non-obese NAFLD in the general population ranged from 25% or lower in some countries such as Malaysia and Pakistan, to over 50% in others like Austria, Mexico, and Sweden. In the general population (individuals with and without NAFLD), 12.1% of the individuals had non-obese NAFLD while 5.1% had lean NAFLD.

The incidence of NAFLD in the non-obese population (without NAFLD at baseline) was estimated as 24.6 per 1000 person-years. Among people with non-obese or lean NALFD, 39.0% had non-alcoholic steatohepatitis, 29.2% had significant fibrosis (stage ≥2), and 3.2% were found to have cirrhosis. Among those with non-obese or lean NAFLD, the incidence of all-cause mortality, liver-related mortality, cardiovascular-related mortality, new-onset diabetes, new-onset cardiovascular disease and new-onset hypertension was 12.1, 4.1, 4.0, 12.6, 18.7, and 56.1 per 1000 person-years, respectively.

Nearly 40% of the global NAFLD population was non-obese and almost one-fifth was lean. Both non-obese and lean groups were found to have considerable long-term liver and non-liver comorbidities.

Therefore, obesity should not be the only criterion for NAFLD screening. Clinical trials of treatments for NAFLD should enrol participants across all ranges of body-mass index.

Source: Ye Q, Zou B, Yeo YH, et al. Global prevalence, incidence, and outcomes of non-obese or lean non-alcoholic fatty liver disease: a systematic review and meta-analysis. Lancet Gastroenterol Hepatol. 2020 May 12. pii: S2468-1253(20)30077-7.