Characteristics of non-obese non-alcoholic fatty liver disease: Effect of genetic and environmental factors

Impact of PNPLA3 in Lean Individuals and in Cryptogenic Steatotic Liver Disease

BACKGROUND

Although metabolic dysfunction-associated steatotic liver disease (MASLD) is strongly associated with obesity, around 20% of individuals with hepatic steatosis may nonetheless have normal body mass index, a condition often referred to as lean nonalcoholic fatty liver disease (NAFLD). Under the new nomenclature and definition of MASLD, lean NAFLD can be further divided into lean MASLD (when there is one or more cardiometabolic risk factors) and cryptogenic steatotic liver disease (when there is no cardiometabolic risk factor).

RESULTS

Current studies suggest that the at-risk PNPLA3 rs738409 variant is more common among individuals with lean NAFLD than their overweight and obese counterparts. However, even in this group, cardiometabolic risk factors are often required for the development of hepatic steatosis and liver injury. In the general population, PNPLA3 gene polymorphism is associated with an increased risk of MASLD, more severe liver histology (i.e., the presence of steatohepatitis and fibrosis) and future development of hepatocellular carcinoma and cirrhotic complications. Emerging data also suggest that individuals carrying the PNPLA3 GG genotype might have a greater reduction in hepatic steatosis and liver enzymes with lifestyle intervention and metabolic treatments, such as glucagon-like peptide-1 receptor agonists.

CONCLUSION

Studies have not specifically examined the impact of PNPLA3 in lean individuals.

Non-Alcoholic Fatty Liver Disease (NAFLD) Management in the Community

Non-alcoholic fatty liver disease (NAFLD) has frequently been associated with obesity, type 2 diabetes (T2D), and dyslipidemia, all of which are shared by increased insulin resistance. It has become the most common liver disorder in Korea as well as in developed countries and is therefore associated with an increased health burden of morbidity and mortality. It has an association with T2D, and T2D increases the risk of cirrhosis and related complications. NAFLD encompasses a disease continuum from simple steatosis to non-alcoholic steatohepatitis which is characterized by faster fibrosis progression. Although its liver-related complication is estimated to be, at most, 10%, it will be a leading cause of cirrhosis and hepatocellular carcinoma soon in Korea. Although the main causes of death in people with NAFLD are cardiovascular disease and extra-hepatic malignancy, advanced liver fibrosis is a key prognostic marker for liver-related outcomes and can be assessed with combinations of non-invasive tests in the community. A number of components of metabolic syndrome involved could be another important prognostic information of NAFLD assessed easily in the routine care of the community. There is a few approved therapies for NAFLD, although several drugs, including antioxidants, attract practitioners' attention. Because of the modest effect of the present therapeutics, let alone complex pathophysiology and substantial heterogeneity of disease phenotypes, combination treatment is a viable option for many patients with NAFLD in the Korean community. Comprehensive approach taking healthy lifestyle and weight reduction into account remain a mainstay to the prevention and treatment of NAFLD.

Central Obesity is an Independent Determinant of Advanced Fibrosis in Lean Patients With Nonalcoholic Fatty Liver Disease

Background

The current definition of lean is based on body mass index (BMI). However, BMI is an imperfect surrogate for adiposity and provides no information on central obesity (CO). Hence, we explored the differences in clinical profile and liver disease severity in lean patients with nonalcoholic fatty liver disease (NAFLD) with and without CO.

Methods

One hundred seventy lean patients with NAFLD (BMI <23 kg/m2) were divided into two groups depending upon the presence or absence of CO (waist circumference ≥80 cm in females and ≥90 cm in males). Noninvasive assessment of steatosis was done by ultrasound and controlled attenuation parameter (CAP), while fibrosis was assessed with FIB-4 and liver stiffness measurement (LSM). FibroScan-AST (FAST) score was used for non-invasive prediction of NASH with significant fibrosis.

Results

Of 170 patients with lean NAFLD, 96 (56.5%) had CO. Female gender (40.6% vs. 17.6%, P = 0.001), hypertriglyceridemia (58.3% vs. 39.2%, P = 0.01) and metabolic syndrome (23.9% vs. 4.1%, P < 0.001) were more common in the CO group. There was a poor correlation between BMI and waist circumference (r = 0.24, 95% CI: 0.09-0.38). Grade 2-3 steatosis on ultrasound was significantly more common in CO patients (30% vs. 12.3%, P = 0.007). CAP [312.5 (289.8-341) dB/m vs. 275 (248-305.1) dB/m, P = 0.002], FAST score [0.42 (0.15-0.66) vs. 0.26 (0.11-0.39), P = 0.04], FIB-4 and LSM were higher in those with CO. Advanced fibrosis was more prevalent among CO patients using FIB-4 (19.8% vs 8.1%, P = 0.03) and LSM (9.5% vs. 0, P = 0.04). CO was independently associated with advanced fibrosis after adjusting for BMI and metabolic risk factors (aOR: 3.11 (1.10-8.96), P = 0.03). Among these 170 patients, 142 fulfilled metabolic dysfunction associated steatotic liver disease (MASLD) criteria. CO was also an independent risk factor for advanced fibrosis in MASLD (3.32 (1.23-8.5), P = 0.02).

Conclusion

Lean patients with NAFLD or MASLD and CO have more severe liver disease compared to those without CO.

Impact of nomenclature as metabolic associated steatotic liver disease on steatotic liver disease prevalence and screening: a prospective population survey in Asians

BACKGROUND AND AIM

The introduction of the latest nomenclature, metabolic associated steatotic liver disease (MASLD), proposed by the multi-society without Asian society consensus statement, aims to redefine the diagnostic criteria for metabolic associated fatty liver disease (MAFLD). However, its effect on the epidemiology in Asia remains unclear.

METHOD

We conducted a population-based cross-sectional survey on fatty liver disease using multistage stratified random sampling of participants from Guangzhou, a representative area in China (ChiCTR2000033376). Demographic, socioeconomic, lifestyle, and laboratory data were collected. Hepatic steatosis and the severity of fibrosis were assessed using FibroScan.

RESULTS

A total of 7388 individuals were recruited, the proportion of which meeting the definitions for nonalcoholic fatty liver disease (NAFLD), MAFLD, and MASLD were 2359 (31.9%), 2666 (36.1%), and 2240 (30.3%), respectively. One hundred and twenty (1.6%) patients had cryptogenic SLD, and 537 (7.3%) patients were diagnosed with MetALD. MASLD did not significantly differ from NAFLD and MAFLD, except that MAFLD patients had a lower proportion of males, hypertension, and diabetes and were less likely to consume tea (P < 0.05). Both cryptogenic SLD and MASLD non-MAFLD patients exhibited milder hepatic steatosis and a lower frequency of liver injury than NAFLD, MAFLD, or MASLD patients (all P < 0.05). An increased HOMA-IR (adjusted OR: 1.33, 95% CI: 1.10-2.03) was associated with higher risk of moderate-to-severe steatosis for MASLD non-MAFLD patients, while consuming more cups of tea (P for trend = 0.015) showed inverse associations.

CONCLUSION

Irrespective of terminology used is that fatty liver disease is highly prevalent in the Han Chinese population. Differences in insulin resistance and lifestyle risk factors are associated with redefinition disparities.

Genetic and Metabolic Characteristics of Lean Nonalcoholic Fatty Liver Disease in a Korean Health Examinee Cohort

Background/Aims

The pathophysiology of lean nonalcoholic fatty liver disease (NAFLD) is unclear but has been shown to be associated with more diverse pathogenic mechanisms than that of obese NAFLD. We investigated the characteristics of genetic or metabolic lean NAFLD in a health checkup cohort.

Methods

This retrospective cross-sectional study analyzed single nucleotide polymorphism data for 6,939 health examinees. Lean individuals were categorized according to a body mass index cutoff of 23 kg/m2. Single nucleotide polymorphisms were analyzed using genotyping arrays.

Results

The prevalence of lean NAFLD was 21.6% among all participants with NAFLD, and the proportion of lean NAFLD was 18.5% among lean participants. The prevalence of metabolic syndrome and diabetes among lean patients with NAFLD was 12.4% and 10.4%, respectively. Lean NAFLD appeared to be metabolic-associated in approximately 20.1% of patients. The homozygous minor allele (GG) of PNPLA3 (rs738409) and heterozygous minor alleles (CT, TT) of TM6SF2 (rs58542926) were associated with lean NAFLD. However, the prevalence of fatty liver was not associated with the genetic variants MBOAT7 (rs641738), HSD17B13 (rs72613567), MARC1 (rs2642438), or AGXT2 (rs2291702) in lean individuals. Lean NAFLD appeared to be associated with PNPLA3 or TM6SF2 genetic variation in approximately 32.1% of cases. Multivariate risk factor analysis showed that metabolic risk factors, genetic risk variants, and waist circumference were independent risk factors for lean NAFLD.

Conclusions

In a considerable number of patients, lean NAFLD did not appear to be associated with known genetic or metabolic risk factors. Further studies are required to investigate additional risk factors and gain a more comprehensive understanding of lean NAFLD.

Unique Genetic Features of Lean NAFLD: A Review of Mechanisms and Clinical Implications

Non-alcoholic fatty liver disease (NAFLD) affects 25% of the global population. About 20% have a normal body mass index (BMI) and a variant known as lean NAFLD. Unlike typical NAFLD cases associated with obesity and diabetes, lean NAFLD causes liver disease by mechanisms not related to excess weight or insulin resistance. Genetic disorders are among the major factors in developing lean NAFLD, and genome-wide association studies have identified several genes associated with the condition. This review aims to increase awareness by describing the genetic markers linked to NAFLD and the defects involved in developing lean NAFLD.

Familial clustering of nonalcoholic fatty liver disease in first-degree relatives of adults with lean nonalcoholic fatty liver disease

BACKGROUND AND AIMS

The heritability of nonalcoholic fatty liver disease (NAFLD) in lean individuals is undetermined. This familial aggregation study aimed to evaluate familial linkage for NAFLD and the risk of NAFLD among first-degree relatives of probands with lean NAFLD.

METHODS

This study prospectively recruited cohorts of probands with lean NAFLD, probands with obese NAFLD, and lean probands with non-NAFLD and their respective first-degree relatives. A total of 257 participants were evaluated for liver steatosis, defined by the controlled attenuation parameter ≥288 dB/m2 , metabolic characteristics, and the PNPLA3, TM6SF2, and MBOAT7 polymorphisms.

RESULTS

The prevalence of NAFLD in first-degree relatives of lean NAFLD probands (39.9%) was similar to that in the obese NAFLD group (36.9%) and was significantly higher than in lean persons without NAFLD (19.1%). First-degree relatives of probands with NAFLD who were male, and had central obesity, hypertriglyceridaemia, insulin resistance, and the PNPLA3 rs738409C>G allele had a significantly higher prevalence of NAFLD. After multivariable adjustment for gender, metabolic characteristics, and the PNPLA3 rs738409C>G allele, first-degree relatives of probands with lean NAFLD (odds ratio [OR], 5.13; 95% CI, 1.77-14.86) and obese NAFLD (OR, 3.20; 95% CI, 1.14-8.99) exhibited an increased risk of NAFLD compared with those of lean controls without NAFLD.

CONCLUSIONS

Our well-phenotype cohorts revealed familial clustering of NAFLD and higher risks of NAFLD in first-degree relatives of probands with lean or obese NAFLD. The findings encourage clinicians caring for NAFLD patients to be more vigilant for NAFLD in their family members.

Lean Indian patients with non-alcoholic fatty liver disease (NAFLD) have less metabolic risk factors but similar liver disease severity as non-lean patients with NAFLD

INTRODUCTION

Although most patients with NAFLD are obese or overweight, some are lean with normal BMI. Our aim was to assess differences in clinicopathological profile and liver disease severity among lean and non-lean NAFLD.

METHODS

Data of 1040 NAFLD patients over last 10 years was analysed. BMI < 23 kg/m2 categorised lean patients. Non-invasive assessment of steatosis was done by ultrasound and controlled attenuation parameter (CAP) while fibrosis was assessed with FIB-4 and liver stiffness measurement (LSM). FibroScan-AST (FAST) score was used for non-invasive prediction of NASH with significant fibrosis. Histology was reported using NASH-CRN system.

RESULTS

149 (14.3%) patients were lean while 891 (85.7%) patients were non-lean. Diabetes mellitus [25 (16.7%) vs 152 (17.05%), p > 0.99], elevated triglycerides [81 (54.3%) vs 525 (58.9%), p = 0.33] and low HDL [71(47.6%) vs 479(53.7%), p = 0.18] were observed in a similar proportion. Lean patients were less likely to have central obesity [72 (48.3%) vs 788 (88.4%), p < 0.001], hypertension [16 (10.7%) vs 239(26.8%), p < 0.001] and metabolic syndrome [21 (14.09%) vs 290 (32.5%), p < 0.001]. No difference in steatosis assessment was noted using ultrasound (p = 0.55) or CAP (0.11). FAST [0.38 (0.18-0.66) vs 0.39 (0.27-0.73), p = 0.53], FIB-4 [1.08 (0.65-1.91) vs 1.09 (0.66-1.94), p = 0.94] and LSM [6.1 (4.8-7.9) vs 6.2 (4.7-8.6), p = 0.19) were similar. Liver biopsy was available in 149 patients [lean: 19 (12.7%), non-lean: 130 (87.3%)]. There was no difference in the number of patients with NASH [4 (21.05%) vs 20 (15.3%), p = 0.51], significant fibrosis [2 (10.5%) vs 32 (24.6%), p = 0.25] or advanced fibrosis [1 (5.26%) vs 18 (13.84%), p = 0.47].

CONCLUSION

Although metabolic co-morbidities are less common, there is no difference in liver disease severity among both groups.

Body Composition Analysis in Patients with Metabolic Dysfunction-Associated Fatty Liver Disease

We sought to examine body composition using bioimpedance analysis in patients with metabolic dysfunction-associated fatty liver disease (MAFLD, 2014 males and 949 females). Factors linked to the fat-free mass index (FF index) were examined using univariate and multivariate analysis. An FF index < 18 kg/m2 in males and an FF index < 15 kg/m2 in females were defined as having decreased skeletal muscle mass. The median age and body mass index (BMI) were 55 years and 25.4 kg/m2 in males, and 57 years and 25.4 kg/m2 in females, respectively. The FF index strongly correlated with muscle mass index both in males (r = 0.999) and females (r = 0.999). The prevalence of patients with an FF index < 18 kg/m2 in males and an FF index < 15 kg/m2 in females was well stratified according to age, BMI, severity of FL, and FIB4 index. In the males, in the multivariate analysis, BMI (p < 0.0001), fat mass index (p < 0.0001), and waist circumference (p = 0.0050) were found to be significant factors linked to FF index. In the females, in the multivariate analysis, BMI (p < 0.0001) and fat mass index (p < 0.0001) were found to be significant. In conclusion, fat accumulation as reflected by BMI, which is an easily available marker, could be a useful indicator for the skeletal muscle mass in MAFLD.

Long working hours and increased risks of lean non-alcoholic fatty liver disease among Korean men and women

Despite the increasing prevalence of lean nonalcoholic fatty liver disease (NAFLD), its risk factors are not well established. We examined the association between long working hours and incident NAFLD in lean Korean workers with emphasis on sex-based effect modification. This cohort study involved 46,113 non-overweight (BMI < 23 kg/m²) and NAFLD-free Korean workers (mean age, 35.5 years). Working hours were categorized into 35-40 (reference), 41-52, and ≥ 53 h. The presence of fatty liver and its severity were determined using ultrasonography and NAFLD fibrosis score (NFS), respectively. Hazard ratios (HRs) and 95% confidence intervals (CIs) were estimated using parametric proportional hazards models. Incident cases of 5901 lean NAFLD developed over a median follow-up of 3.8 years. The incidence of lean NAFLD increased with increasing working hours with a stronger association in men than in women (P for interaction < 0.001). For men, multivariable-adjusted HRs (95% CIs) for lean NAFLD in time-dependent models comparing working hours of 41-52 and ≥ 53 h compared to the reference category were 1.17 (1.07-1.28) and 1.25 (1.12-1.39), respectively. The excess relative risk of developing lean NAFLD with intermediate/high NFS was observed in working hours of 41-52 and ≥ 53 h with a corresponding HR of 1.66 (1.13-2.43) and 1.54 (0.94-2.51), respectively. Conversely, no significant associations were found between working hours and incidence of lean NAFLD in women. In conclusion, long working hours were significantly associated with an increased incidence of lean NAFLD and its severe form in men but not in women.

Genetic variants in HFE are associated with non-alcoholic fatty liver disease in lean individuals

Background & Aims

Around 20% of patients with non-alcoholic fatty liver disease (NAFLD) are lean. Increasing evidence suggests that lean NAFLD is a unique subtype of the disease. We aimed to explore the metabolic profile, genetic basis, causal risk factors, and clinical sequelae underlying lean NAFLD.

Methods

NAFLD was diagnosed by whole liver proton density fat fraction ≥5%. Whole liver proton density fat fraction and hepatic iron were quantified using magnetic resonance imaging in the UK Biobank. Individuals in this study were stratified according to the World Health Organization criteria of obesity, into lean, overweight, and obese. Mediation analysis, Mendelian randomisation analysis, and Bayesian networks were used to identify a risk factor or a clinical sequela of lean/obese NAFLD.

Results

Lean NAFLD manifested a distinct metabolic profile, featured by elevated hepatic iron and fasting glucose. Four loci, namely, HFE rs1800562, SLC17A3-SLC17A2-TRIM38 rs9348697, PNPLA3 rs738409, and TM6SF2 rs58542926, were associated with lean NAFLD (p <5 × 10^-8). HFE rs1800562 was specifically associated with lean NAFLD and demonstrated a significant mediation effect through elevating hepatic iron. Type 2 diabetes was the most pronounced clinical sequela of lean NAFLD, followed by liver cirrhosis.

Conclusions

Our study suggested that HFE plays a potential steatogenic role rather than regulating iron homoeostasis in patients with lean NAFLD. The increased liver iron deposition is associated with lean NAFLD, whereas obese NAFLD is not related to hepatic iron. The clinical management of patients with lean NAFLD shall be concerned with the prevention and treatment of type 2 diabetes and liver cirrhosis.

Impact and implications

Lean NAFLD has a distinct natural history from obese NAFLD. This study underscored liver iron content and the genetic variant of the iron homoeostasis gene HFE as major risks of lean NAFLD, in addition to the unique metabolic profile. The development of type 2 diabetes or liver cirrhosis shall be closely monitored and prevented in patients with lean NAFLD.

Non-alcoholic fatty liver disease is associated with an increased risk of type 2 diabetes

OBJECTIVE

Non-alcoholic fatty liver disease (NAFLD) has become the most common liver disease worldwide and represents the leading cause of liver-related morbidity and mortality. Its all-cause mortality is often driven by co-existing metabolic diseases such as type 2 diabetes (T2DM), which share many pathophysiological characteristics. The risk of developing T2DM among NAFLD patients in Germany is only poorly described.

METHODS

A cohort of 17 245 NAFLD patients and a propensity score-matched cohort of equal size were identified from the Disease Analyzer database (IQVIA) between 2005 and 2020. The incidence of T2DM was evaluated as a function of NAFLD during a 5-year study period using Cox-regression models.

RESULTS

Within 5 years of the index date, 18.8% and 11.7% of individuals with and without NAFLD were diagnosed with T2DM ( P  < 0.001). Regression analysis revealed a hazard ratio of 1.77 [95% confidence interval (CI), 1.68-1.88] for the development of T2DM among NAFLD patients. Subgroup analyses confirmed this association for all age groups (18-50, 51-60, 61-70 and >70 years), male and female patients, as well as normal weight (BMI < 25 kg/m 2 ), overweighted (BMI 25-30 kg/m 2 ) and obese (BMI > 30 kg/m 2 ) patients.

CONCLUSION

Our data revealed a significantly increased incidence of T2DM among NAFLD patients in Germany. Given the dramatically increasing global relevance of NAFLD, we believe that prevention and regular screening programs for T2DM in NAFLD patients could help to reduce its high mortality and morbidity in the future.

Special Population: Lean Nonalcoholic Fatty Liver Disease

Nonalcoholic fatty liver disease (NAFLD) is strongly associated with obesity but around 10% to 20% of patients with NAFLD have normal body mass index, a condition referred to as lean or nonobese NAFLD. Although lean patients more often have milder liver disease, a proportion may nonetheless develop steatohepatitis and advanced liver fibrosis. Both genetic and environmental factors contribute to the development of NAFLD. Noninvasive tests have similarly good accuracy as initial assessments for lean NAFLD. Future studies should determine the most appropriate treatment in this special population.

Nonalcoholic Fatty Liver Disease in Lean/Nonobese and Obese Individuals: A Comprehensive Review on Prevalence, Pathogenesis, Clinical Outcomes, and Treatment

Nonalcoholic fatty liver disease (NAFLD) is the most common liver disease worldwide, with an estimated prevalence of 25% globally. NAFLD is closely associated with metabolic syndrome, which are both becoming increasingly more common with increasing rates of insulin resistance, dyslipidemia, and hypertension. Although NAFLD is strongly associated with obesity, lean or nonobese NAFLD is a relatively new phenotype and occurs in patients without increased waist circumference and with or without visceral fat. Currently, there is limited literature comparing and illustrating the differences between lean/nonobese and obese NAFLD patients with regard to risk factors, pathophysiology, and clinical outcomes. In this review, we aim to define and further delineate different phenotypes of NAFLD and present a comprehensive review on the prevalence, incidence, risk factors, genetic predisposition, and pathophysiology. Furthermore, we discuss and compare the clinical outcomes, such as insulin resistance, dyslipidemia, hypertension, coronary artery disease, mortality, and progression to nonalcoholic steatohepatitis, among lean/nonobese and obese NAFLD patients. Finally, we summarize the most up to date current management of NAFLD, including lifestyle interventions, pharmacologic therapies, and surgical options.

Outcomes of subjects who are lean, overweight or obese with nonalcoholic fatty liver disease: A cohort study in China

The ability to determine the prognosis of lean nonalcoholic fatty liver disease (NAFLD) is essential for decision making in clinical settings. Using a large community-based Chinese cohort, we aimed to investigate NAFLD outcomes by body mass index (BMI). We used the restricted cubic splines method to investigate the dose-response relationship between BMI and outcomes in subjects with NAFLD and those without NAFLD. We included 73,907 subjects from the Kailuan cohort and grouped all subjects into four phenotypes by using NAFLD and BMI (<23 kg/m² ). The probability of developing outcomes for individuals with lean NAFLD (LN), overweight/obese NAFLD (ON), overweight/obese non-NAFLD (ONN), and lean non-NAFLD (LNN) was estimated. We found a U-shaped association between BMI and death but a linear positive association concerning cardiovascular disease (CVD) after adjusting for age and other covariates. Compared with the LNN group, the adjusted hazard ratios (HRs) and 95% confidence intervals (CIs) of the LN, ON, and ONN groups were 1.30 (1.14-1.49), 0.86 (0.80-0.91), 0.84 (0.80-0.89) for all-cause death, 2.61 (1.13-6.03), 0.74 (0.44-1.26), 1.10 (0.70-1.74) for liver-related death, 2.12 (1.46-3.08), 1.23 (0.99-1.54), 1.19 (0.98-1.43) for digestive system cancers, and 2.04 (1.40-2.96), 1.30 (1.05-1.61), 1.21 (1.01-1.46) for obesity-related cancers. Subjects with LN had a significantly higher risk of colorectal cancer and esophagus cancer. However, the ON group had the highest CVD risk (HR, 1.39; 95% CI, 1.27-1.52). The LN group with hypertension had a higher risk of adverse outcomes, and those without hypertension had a similar risk compared to LNN. Conclusion: Subjects with LN may experience a higher risk of all-cause death, digestive system cancers, and obesity-related cancers than the other three groups but a lower risk of CVD than ON subjects. LN with hypertension may be a high-risk phenotype.

Most Cases of Cryptogenic Cirrhosis May be Nonobese Nonalcoholic Steatohepatitis-Risk Factors of Liver Steatosis After Liver Transplantation for Cryptogenic Cirrhosis: A Retrospective Study

Aim The course of cryptogenic cirrhosis (CC) after liver transplantation (LT) is unknown. We therefore clarified the natural course post-LT for CC and investigated the etiology of CC. Methods Eighteen patients who underwent LT for CC were included. To rule out the possibility of NASH in patients with CC, those with a history of obesity or liver steatosis found pretransplantation were excluded. A liver biopsy was performed one year after LT and annually thereafter. Results Liver steatosis and steatohepatitis were identified in 61% and 39% of patients after LT, respectively, with a median time to the onset of 12 and 27 months, respectively. There were no other pathological findings such as liver allograft rejection, autoimmune hepatitis, or primary biliary cholangitis. The body mass index after LT (28.5 vs. 22.4 kg/m²; P=0.002) and mean muscle attenuation at the time of LT were significantly higher (33.3 vs. 25.8 Hounsfield units, P=0.03) and the postoperative hospitalization period shorter (50 vs. 102 days; P=0.02) in the steatosis group than in the non-steatosis group. Recipients were significantly younger in the steatohepatitis subgroup than in the simple steatosis subgroup (55.0 vs. 63.5 years old; P=0.04). Conclusions Despite excluding CC patients with a history of obesity, we observed that patients with CC had a high prevalence of steatosis after LT than those without CC. Young patients with a favorable postoperative course were noted to have a high risk of NASH after LT for CC. Patients with CC may represent cases of non-obese NASH.

Comparison of long‐term prognosis between non‐obese and obese patients with non‐alcoholic fatty liver disease

Background and Aim

Non‐alcoholic fatty liver disease (NAFLD) can progress in non‐obese patients as in obese patients. Reports on long‐term prognosis in non‐obese NAFLD patients are controversial. Therefore, we aimed to examine the long‐term prognosis of non‐obese patients with NAFLD.

Methods

This single‐center, retrospective cohort study enrolled biopsy‐proven non‐obese and obese NAFLD patients between January 2002 and December 2011 and followed them up until 31 March 2021, for death and clinical events (cardiovascular and liver‐related events and extrahepatic cancers).

Results

Of the 223 NAFLD patients, 58 (26.0%) were non‐obese. Compared with obese patients, they had a lower fibrosis stage (0.8 ± 0.80 vs 1.2 ± 0.91; P = 0.004), milder lobular inflammation (0.9 ± 0.7 vs 1.1 ± 0.7; P = 0.02), and significantly lower serum creatinine, total bilirubin, ferritin, and type IV collagen 7S and higher high‐density lipoprotein levels. After a median follow‐up of 8.9 years, no significant difference was noted in mortality between the two groups (2 [3.4%] non‐obese vs 5 [3.0%] obese; log‐rank test, P = 0.63). Twelve patients (20.7%) in the non‐obese group and 32 (19.4%) in the obese group had clinical events. Although the obese group had a higher incidence of clinical events during the first 10 years of follow‐up, the non‐obese group had a higher incidence after that (log‐rank test, P = 0.67). The non‐obese group had a high incidence of malignancy (9 [15.5%] non‐obese vs 14 [8.3%] obese; P = 0.13).

Conclusion

Non‐obese NAFLD does not necessarily have a good prognosis, and some cases have a poor prognosis such as extrahepatic cancers. Further validation is required in the future.

New Insights into Non-Alcoholic Fatty Liver Disease and Coronary Artery Disease: The Liver-Heart Axis

Non-alcoholic fatty liver disease (NAFLD) represents the hepatic expression of the metabolic syndrome and is the most prevalent liver disease. NAFLD is associated with liver-related and extrahepatic morbi-mortality. Among extrahepatic complications, cardiovascular disease (CVD) is the primary cause of mortality in patients with NAFLD. The most frequent clinical expression of CVD is the coronary artery disease (CAD). Epidemiological data support a link between CAD and NAFLD, underlain by pathogenic factors, such as the exacerbation of insulin resistance, genetic phenotype, oxidative stress, atherogenic dyslipidemia, pro-inflammatory mediators, and gut microbiota. A thorough assessment of cardiovascular risk and identification of all forms of CVD, especially CAD, are needed in all patients with NAFLD regardless of their metabolic status. Therefore, this narrative review aims to examine the available data on CAD seen in patients with NAFLD, to outline the main directions undertaken by the CVD risk assessment and the multiple putative underlying mechanisms implicated in the relationship between CAD and NAFLD, and to raise awareness about this underestimated association between two major, frequent and severe diseases.

Comparative Burden of Metabolic Dysfunction in Lean NAFLD vs Non-lean NAFLD - A Systematic Review and Meta-analysis

BACKGROUND & AIMS

Nonalcoholic fatty liver disease (NAFLD) is traditionally associated with obesity. However, there is a subtype of NAFLD, namely NAFLD in lean, that occurs without obesity. However, a recent call to redefine NAFLD to metabolic-associated fatty liver disease focuses on obesity and metabolic dysfunction. Criticism has arisen from the perceived over emphasis on systemic comorbidities, which may disadvantage the lean. The current analysis seeks to quantify the degree of metabolic dysfunction in NAFLD in lean and compare with NAFLD in overweight and obese and non-NAFLD.

METHODS

Medline and Embase databases were searched from inception to March 3, 2022. The inclusion criteria were articles with NAFLD in lean patients presenting with baseline metabolic parameters. Comparisons were conducted with subgroup analysis.

RESULTS

Eighty-five articles were included in the meta-analysis. NAFLD in lean accounted for 13.11% (95% confidence interval [CI], 10.26%-16.62%) of the global population and 14.55% (95% CI, 11.32%-18.51%) in Asia. The degree of metabolic dysfunction was weight dependent with significantly less metabolic dysfunction in NAFLD in lean subjects as compared with NAFLD in overweight counterparts. For NAFLD in lean, only 19.56% (95% CI, 15.28%-24.69%) of the subjects were diabetic, whereas 45.70% (95% CI, 35.01%-56.80%) of obese subjects with NAFLD had diabetes (P < .01). Fasting blood glucose and systolic and diastolic blood pressure values were significantly lower in subjects with NAFLD in lean than in overweight and obese.

CONCLUSION

The current analysis highlights the weight-dependent nature of metabolic dysfunction in NAFLD. Lean subjects with NAFLD were significantly less metabolically unhealthy than were obese and overweight persons with NAFLD. An overreliance on metabolic dysfunction in defining fatty liver will be a flaw in potentially excluding previously characterized NAFLD.

Associations of body shape index (ABSI) and hip index with liver, metabolic, and inflammatory biomarkers in the UK Biobank cohort

Associations of liver, metabolic, and inflammatory biomarkers in blood with body shape are unclear, because waist circumference (WC) and hip circumference (HC) are dependent on overall body size, resulting in bias. We have used the allometric "a body shape index" (ABSI = WC_(mm)[Formula: see text]Weight_(kg)^-2/3[Formula: see text]Height_(m)^5/6) and hip index (HI_women = HC_(cm)[Formula: see text]Weight_(kg)^-0.482[Formula: see text]Height_(cm)^0.310, HI_men = HC_(cm)[Formula: see text]Weight_(kg)^-2/5[Formula: see text]Height_(cm)^1/5), which are independent of body mass index (BMI) by design, in multivariable linear regression models for 121,879 UK Biobank men and 135,559 women. Glucose, glycated haemoglobin (HbA1c), triglycerides, low-density-lipoprotein cholesterol, apolipoprotein-B, alanine aminotransferase (ALT), gamma-glutamyltransferase, and lymphocytes were associated positively with BMI and ABSI but inversely with HI. High-density-lipoprotein cholesterol and apolipoprotein-A1 were associated inversely with BMI and ABSI but positively with HI. Lipid-related biomarkers and ALT were associated only with HI in obese men. C-reactive protein, neutrophils, monocytes, and alkaline phosphatase were associated positively, while bilirubin was associated inversely, with BMI and ABSI but not with HI. Associations were consistent within the clinical reference ranges but were lost or changed direction for low or high biomarker levels. Our study confirms associations with waist and hip size, independent of BMI, for metabolic biomarkers but only with waist size for inflammatory biomarkers, suggesting different contribution of the mechanistic pathways related to body shape.

Association of Low Skeletal Muscle Mass with the Phenotype of Lean Non-Alcoholic Fatty Liver Disease

Low skeletal muscle mass (LSMM) has emerged as a potential risk factor for non-alcoholic fatty liver disease (NAFLD). However, its clinical implications in patients with lean NAFLD have not yet been elucidated. We investigated the role of LSMM in patients with lean NAFLD. Lean NAFLD was defined as a body mass index of ≤23 kg/m2. Using bioelectrical impedance analysis, the appendicular skeletal muscle mass (ASM) was adjusted by height squared. The LSMM was based on 1 SD below the sex-specific mean for young, healthy Asian adults. Of the 8905 ultrasound-confirmed NAFLD patients, 3670 (41.2%) were diagnosed with lean NAFLD. The lean NAFLD group was younger (45.0 vs. 49.0 years, p < 0.001), and had a lower waist circumference (74.0 vs. 85.0 cm, p < 0.001), lower prevalence of diabetes (3.1 vs. 7.4%, p < 0.001) and hypertension (4.2 vs. 15.2%, p < 0.001), and a higher proportion of LSMM (28.0 vs. 2.2%, p < 0.001) than the non-lean NAFLD group. Stepwise adjusted models suggested that LSMM was associated with lean individuals with NAFLD (odds ratio = 7.02, p < 0.001). LSMM may be a novel risk factor for lean NAFLD patients more than non-lean NAFLD patients, independent of classic metabolic factors.

MAFLD: Renovation of clinical practice and disease awareness of fatty liver

Recently, international expert panels have proposed a new definition of fatty liver: metabolic dysfunction-associated fatty liver disease (MAFLD). MAFLD is not just a simple renaming of non-alcoholic fatty liver disease (NAFLD). The unique feature of MAFLD is the inclusion of metabolic dysfunctions, which are high-risk factors for events. In addition, MAFLD is independent of alcohol intake and the co-existing causes of liver disease. This new concept of MAFLD may have a widespread impact on patients, medical doctors, medical staff, and various stakeholders regarding fatty liver. Thus, MAFLD may renovate clinical practice and disease awareness of fatty liver. In this review, we introduce the definition of and rationale for MAFLD. We further describe representative cases showing how the diagnostic processes differ between MAFLD and NAFLD. We also summarize recent studies comparing MAFLD with NAFLD and discuss the impact of MAFLD on clinical trials, Japanese populations, and disease awareness.

NAFLD in normal weight individuals

Nonalcoholic fatty liver disease (NAFLD) can develop in lean individuals. Despite a better metabolic profile, the risk of disease progression to hepatic inflammation, fibrosis, and decompensated cirrhosis in the lean is similar to that in obesity-related NAFLD and lean individuals may experience more severe hepatic consequences and higher mortality relative to those with a higher body mass index (BMI). In the absence of early symptoms and abnormal laboratory findings, lean individuals are not likely to be screened for NAFLD or related comorbidities; however, given the progressive nature of the disease and the increased risk of morbidity and mortality, a clearer understanding of the natural history of NAFLD in lean individuals, as well as efforts to raise awareness of the potential health risks of NAFLD in lean individuals, are warranted. In this review, we summarize available data on NAFLD prevalence, clinical characteristics, outcomes, and mortality in lean individuals and discuss factors that may contribute to the development of NAFLD in this population, including links between dietary and genetic factors, menopausal status, and ethnicity. We also highlight the need for greater representation of lean individuals in NAFLD-related clinical trials, as well as more studies to better characterize lean NAFLD, develop improved screening algorithms, and determine specific treatment strategies based on underlying etiology.

Is there an 'ideal' diet for patients with NAFLD?

Nonalcoholic fatty liver disease (NAFLD) is a growing epidemic that encompasses three distinct clinical phenotypes: uncomplicated fatty liver, nonalcoholic steatohepatitis (NASH) and NASH-related cirrhosis with its complications, including hepatocellular carcinoma. To date, no pharmacological treatments have been approved and lifestyle modifications including reduced caloric intake targeting a 7%-10% weight loss from baseline assessment represent the standard approach. Mediterranean diet has been recommended as the best dietary pattern since it is easy to follow and, independently of caloric intake its nutritional components have beneficial metabolic effects that not only improve steatosis but also risk factors for cardiovascular events, the leading cause of morbidity/mortality in individuals with NAFLD. Other dietary patterns such as ketogenic diet and Dietary Approach to Stop Hypertension (DASH) diet can be used in patients with NAFLD. Recently, intermittent fasting diets have gained popularity among healthy individuals and have been proposed as a safe and effective treatment for the metabolic syndrome in experimental and in a few human studies. In this narrative review, we aim to summarize the evidence for the available dietary approaches for patients with NAFLD.

Association of genetic variations with NAFLD in lean individuals

BACKGROUND & AIMS

How adiposity influences the effect of genetic variants on non-alcoholic fatty liver disease (NAFLD) in the Asian population remains unclear. We aimed to study the association between genetic risk variants and susceptibility/severity of NAFLD in the lean, overweight and obese individuals.

METHODS

Nine hundred and four community subjects underwent proton-magnetic resonance spectroscopy and transient elastography examination. Lean (<23 kg/m2 ), overweight (23-24.9 kg/m2 ) and obesity (≥25 kg/m2 ) were defined according to the body mass index cut-offs for Asians. NAFLD was defined as intrahepatic triglycerides ≥5%. PNPLA3, TM6SF2, MBOAT7 and 9 other gene polymorphisms were analysed by rhAMPTM SNP assays.

RESULTS

Five hundred and twenty-nine (58.5%), 162 (17.9%) and 213 (23.6%) subjects were lean, overweight and obese, respectively. The prevalence of NAFLD was 12.4%, 41.4% and 59.1% in the three groups (P < .001). Amongst those with NAFLD, lean subjects (30.3%) were more likely to carry the PNPLA3 rs738409 GG genotype than overweight (17.9%) and obese subjects (17.4%) (P = .003). Compared with the CC genotype, the GG genotype was associated with the greatest increase in the risk of NAFLD in lean subjects (odds ratio [OR] 6.04), compared with overweight (OR 3.43, 95% CI [1.06, 11.14]) and obese subjects (OR 2.51, 95% CI [0.93, 6.78]). Additionally, the TM6SF2 rs58542926 TT genotype was associated with reduced serum triglycerides only in lean subjects. A gene-BMI effect was not observed for the other gene polymorphisms.

CONCLUSIONS

The PNPLA3 rs738409 gene polymorphism has a greater effect on liver fat in Asian lean individuals than in overweight or obese ones.

Heterogeneity of non-alcoholic fatty liver disease: Implications for clinical practice and research activity

Non-alcoholic fatty liver disease (NAFLD) is a heterogeneous condition with a wide spectrum of clinical presentations and natural history and disease severity. There is also substantial inter-individual variation and variable response to a different therapy. This heterogeneity of NAFLD is in turn influenced by various factors primarily demographic/dietary factors, metabolic status, gut microbiome, genetic predisposition together with epigenetic factors. The differential impact of these factors over a variable period of time influences the clinical phenotype and natural history. Failure to address heterogeneity partly explains the sub-optimal response to current and emerging therapies for fatty liver disease. Consequently, leading experts across the globe have recently suggested a change in nomenclature of NAFLD to metabolic-associated fatty liver disease (MAFLD) which can better reflect current knowledge of heterogeneity and does not exclude concomitant factors for fatty liver disease (e.g. alcohol, viral hepatitis, etc.). Precise identification of disease phenotypes is likely to facilitate clinical trial recruitment and expedite translational research for the development of novel and effective therapies for NAFLD/MAFLD.

Risk factors of nonalcoholic fatty liver disease in lean body mass population: A systematic review and meta-analysis

The pathophysiology and risk factors of nonalcoholic fatty liver disease (NAFLD) among lean patients is poorly understood and therefore investigated. We performed a meta-analysis of observational studies. Of 1175 articles found through searching from Medline/PubMed, Banglajol, and Google Scholar by two independent investigators, 22 were selected. Data from lean (n = 6768) and obese (n = 9253) patients with NAFLD were analyzed; lean (n = 43 398) and obese (n = 9619) subjects without NAFLD served as controls. Age, body mass index, waist circumference, systolic blood pressure, and diastolic blood pressure (DBP) had significantly higher estimates in lean NAFLD patients than in lean non-NAFLD controls. Fasting blood sugar [MD(mean difference) 5.17 mg/dl, 95% CI(confidence interval) 4.14-6.16], HbA1c [MD 0.29%, 95% CI 0.11-0.48], and insulin resistance [HOMA-IR] [MD 0.49 U, 95% CI 0.29-0.68]) were higher in lean NAFLD patients than in lean non-NAFLD controls. All components of the lipid profile were raised significantly in the former group except high-density lipoprotein. An increased uric acid (UA) level was found to be associated with the presence of NAFLD among lean. Cardio-metabolic profiles of nonlean NAFLD patients significantly differs from the counter group. However, the magnitude of the difference of lipid and glycemic profile barely reached statistical significance when subjects were grouped according to lean and nonlean NAFLD. But DBP (slope: 0.19, P < 0.037), HOMA-IR (slope: 0.58, P < 0.001), and UA (slope: 0.36, P = 0.022) were significantly higher if NAFLD was present compared to that of non-NAFLD group. Lean and nonlean NAFLD patients are metabolically similar and share common risk factors.

Emerging Role of Genomic Analysis in Clinical Evaluation of Lean Individuals With NAFLD

Whereas the rising prevalence of nonalcoholic fatty liver disease (NAFLD) is closely related with the global obesity epidemic, up to 10–20% of individuals with NAFLD are lean as defined by a body mass index of < 25 kg/m2, or < 23 kg/m2 in Asians. This entity designated as “lean NAFLD” is estimated to affect 8 to 10 million individuals in the United States alone. Here, we review the emerging data on the epidemiology, natural history and prognosis of lean NAFLD and put forward a diagnostic approach that combines detailed clinical phenotyping with genomic analysis. We propose two subtypes of lean NAFLD referred to as type 1: individuals with visceral adiposity and insulin resistance but normal BMI; and type 2: lean individuals with hepatic steatosis secondary to a known or unknown monogenic disease. We envision that incorporation of genomic analysis in the diagnostic algorithm of lean patients with NAFLD will elucidate the contribution of common genetic variants through the calculation of NAFLD polygenic risk score and also characterize the diverse array of rare monogenic diseases that can lead to triglyceride accumulation in the cytoplasm of hepatocytes. Collectively, the integration of a molecular diagnosis in the clinical evaluation of patients with lean NAFLD will provide an accurate diagnosis, with possible targeted therapies and may uncover novel molecular mechanisms with potential broader therapeutic implications.

Non-Alcoholic Fatty Liver Disease in Lean and Non-Obese Individuals: Current and Future Challenges

Non-alcoholic fatty liver disease (NAFLD), which approximately affects a quarter of the world’s population, has become a major public health concern. Although usually associated with excess body weight, it may also affect normal-weight individuals, a condition termed as lean/non-obese NAFLD. The prevalence of lean/non-obese NAFLD is around 20% within the NAFLD population, and 5% within the general population. Recent data suggest that individuals with lean NAFLD, despite the absence of obesity, exhibit similar cardiovascular- and cancer-related mortality compared to obese NAFLD individuals and increased all-cause mortality risk. Lean and obese NAFLD individuals share several metabolic abnormalities, but present dissimilarities in genetic predisposition, body composition, gut microbiota, and susceptibility to environmental factors. Current treatment of lean NAFLD is aimed at improving overall fitness and decreasing visceral adiposity, with weight loss strategies being the cornerstone of treatment. Moreover, several drugs including PPAR agonists, SGLT2 inhibitors, or GLP-1 receptor agonists could also be useful in the management of lean NAFLD. Although there has been an increase in research regarding lean NAFLD, there are still more questions than answers. There are several potential drugs for NAFLD therapy, but clinical trials are needed to evaluate their efficacy in lean individuals.

Association between PNPLA3 rs738409 polymorphism and nonalcoholic fatty liver disease: a systematic review and meta-analysis

BACKGROUND

Non-alcoholic fatty liver disease (NAFLD) is a common disorder that is known to be the leading cause of chronic liver disease worldwide. This study aims to systematically review and meta-analyze the association between PNPLA3 rs738409 polymorphism and non-alcoholic fatty liver.

METHODS

Following a systematic review and meta-analysis method, articles without any time limitation, were extracted from SID, MagIran, IranDoc, Scopus, Embase, Web of Science (WoS), PubMed and ScienceDirect international databases. Random effects model was used for analysis, and heterogeneity of studies was investigated considering the I² index and using Comprehensive Meta-Analysis software.

RESULTS

The odds ratio of CC genotype in patients with non-alcoholic fatty liver demonstrates the protective effect of CC genotype with the ratio of 0.52, whereas CG genotype presents an increasing effect of CG genotype with the ratio of 0.19, and GG genotype also showed an increasing effect of GG genotype with the ratio of 1.05. Moreover, CG + GG genotypes as a single group demostrated an odds rartio of 0.88.

CONCLUSION

This meta-analysis highlights that people with CC genotype has 52% lower chance of developing non-alcoholic fatty liver disease, and those with CG genotype had 19% higher risk of developing non-alcoholic fatty liver. Those with GG genotype were 105% more likely to develop non-alcoholic fatty liver than others. Moreover, those present in a population with CG + GG genotypes were 88% more likely to have non-alcoholic fatty liver disease.

Lean NAFLD: an underrecognized and challenging disorder in medicine

Classically, Non-Alcoholic Fatty Liver Disease (NAFLD) has been thought to be driven by excessive weight gain and obesity. The overall greater awareness of this disorder has led to its recognition in patients with normal body mass index (BMI). Ongoing research has helped to better understand potential causes of Lean NAFLD, the risks for more advanced disease, and potential therapies. Here we review the recent literature on prevalence, risk factors, severity of disease, and potential therapeutic interventions.

The metabolic profiles and body composition of lean metabolic associated fatty liver disease

BACKGROUND/PURPOSE

Metabolic associated fatty liver disease (MAFLD) is the commonest cause of chronic liver disease, which is associated with obesity and diabetes. However, it also occurs in lean individuals especially in Asian populations.

METHODS

The participants of Tzu Chi MAFLD cohort (TCMC) including health controls or MAFLD patients were enrolled. MAFLD was defined as fatty liver in imaging without hepatitis B virus, hepatitis C virus infection, drug, alcohol or other known causes of chronic liver disease. Lean MAFLD was defined as MAFLD in lean subjects (BMI < 23 kg/m²).

RESULTS

A total of 880 subjects were included for final analysis. Of 394 MAFLD patients, 65 (16.5%) patients were diagnosed as lean MAFLD. Lean MAFLD patients were elder, higher percentage of female gender, lower ALT, diastolic blood pressure, triglyceride, and waist circumference but higher HDL than non-lean MAFLD patients. Using binary regression analysis, elder age and lower waist circumference were associated with lean MAFLD. Compared with lean healthy controls, lean MAFLD patients had higher BMI, waist circumference, and percentage of hypertension. In body composition, fatty tissue index (FTI), lean tissue index (LTI) ,and total body water (TBW) were lower in lean MAFLD than non-lean MAFLD patients; but they were comparable with lean healthy controls.

CONCLUSIONS

The prevalence of lean MAFLD was 16.5% in this study population and it was higher in elder age, especially of female subjects. Lean MAFLD patients had different metabolic profiles compared with lean healthy controls, but different body composition compared with non-lean MAFLD patients.

Nonalcoholic Fatty Liver Disease: A Global Perspective

The prevalence of nonalcoholic fatty liver disease (NAFLD) has been increasing over the years and is now as high in Asia as in the Western world, so much so that it should no longer be considered a Western disease. In fact, China is expected to have the largest increase in the number of NAFLD cases in the coming years. The increase in prevalence of NAFLD in Asia lags behind that of the Western world; thus, there will be a lag in more severe liver disease in Asia despite a similar prevalence of the disease. NAFLD is more prevalent among patients with diabetes mellitus, which is also an important risk factor for more severe liver disease. Patients with diabetes mellitus thus represent an important target for screening for NAFLD and more severe liver disease. Although the PNPLA3 gene polymorphism is the most studied in NAFLD, it is increasingly clear that the cumulative effect of multiple genes likely predisposes to NAFLD and more severe liver disease in the different ethnic groups, and polygenic risk scores are emerging. Lean NAFLD has been largely reported in Asia but is increasingly recognized worldwide. Multiple risk factors have been identified for the disease that manifests in metabolically unhealthy normal weight individuals; however, it responds to lifestyle intervention, similar to the disease in obese individuals. Lastly, the newer term "metabolic dysfunction-associated fatty liver disease" provides a more accurate reflection of the disease, giving more focus to clinicians and researchers in tackling this increasingly common and challenging disease.

Nonalcoholic fatty liver disease in lean subjects: Prognosis, outcomes and management

Nonalcoholic fatty liver disease (NAFLD) accounts for most cases of chronic liver disease worldwide, with an estimated global prevalence of approximately 25% and ranges from simple steatosis to nonalcoholic steatohepatitis and cirrhosis. NAFLD is strongly connected to metabolic syndrome, and for many years, fatty liver was considered to be an exclusive feature of obese patients. However, recent studies have highlighted the presence of NAFLD in non-obese subjects, with or without increased visceral fat or even in lean subjects without increased waist circumference. "Lean NAFLD" is a relatively new concept and there is significant scientific interest in understanding the differences in pathophysiology, prognosis and management compared with NAFLD in overweight/obese patients. In the present editorial, we discuss the clinical and metabolic profiles and outcomes of lean NAFLD compared with both obese NAFLD and lean healthy individuals from Asian and Western countries. Moreover, we shed light to the challenging topic of management of NAFLD in lean subjects since there are no specific guidelines for this population. Finally, we discuss open questions and issues to be addressed in the future in order to categorize NAFLD patients into lean and non-lean cohorts.

Rescue of Hepatic Phospholipid Remodeling Defectin iPLA2β-Null Mice Attenuates Obese but Not Non-Obese Fatty Liver

Polymorphisms of group VIA calcium-independent phospholipase A2 (iPLA₂β or PLA2G6) are positively associated with adiposity, blood lipids, and Type-2 diabetes. The ubiquitously expressed iPLA₂β catalyzes the hydrolysis of phospholipids (PLs) to generate a fatty acid and a lysoPL. We studied the role of iPLA₂β on PL metabolism in non-alcoholic fatty liver disease (NAFLD). By using global deletion iPLA₂β-null mice, we investigated three NAFLD mouse models; genetic Ob/Ob and long-term high-fat-diet (HFD) feeding (representing obese NAFLD) as well as feeding with methionine- and choline-deficient (MCD) diet (representing non-obese NAFLD). A decrease of hepatic PLs containing monounsaturated- and polyunsaturated fatty acids and a decrease of the ratio between PLs and cholesterol esters were observed in all three NAFLD models. iPLA₂β deficiency rescued these decreases in obese, but not in non-obese, NAFLD models. iPLA₂β deficiency elicited protection against fatty liver and obesity in the order of Ob/Ob › HFD » MCD. Liver inflammation was not protected in HFD NAFLD, and that liver fibrosis was even exaggerated in non-obese MCD model. Thus, the rescue of hepatic PL remodeling defect observed in iPLA₂β-null mice was critical for the protection against NAFLD and obesity. However, iPLA₂β deletion in specific cell types such as macrophages may render liver inflammation and fibrosis, independent of steatosis protection.

Global prevalence, incidence, and outcomes of non-obese or lean non-alcoholic fatty liver disease: a systematic review and meta-analysis

BACKGROUND

Although non-alcoholic fatty liver disease (NAFLD) is commonly associated with obesity, it is increasingly being identified in non-obese individuals. We aimed to characterise the prevalence, incidence, and long-term outcomes of non-obese or lean NAFLD at a global level.

METHODS

For this systematic review and meta-analysis, we searched PubMed, Embase, Scopus, and the Cochrane Library from inception to May 1, 2019, for relevant original research articles without any language restrictions. The literature search and data extraction were done independently by two investigators. Primary outcomes were the 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. We also aimed to characterise the demographic, clinical, and histological characteristics of individuals with non-obese NAFLD.

FINDINGS

We identified 93 studies (n=10 576 383) from 24 countries or areas: 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) were used for the outcomes analysis. Within the NAFLD population, 19·2% (95% CI 15·9-23·0) of people were lean and 40·8% (36·6-45·1) were non-obese. The prevalence of non-obese NAFLD in the general population varied from 25% or lower in some countries (eg, Malaysia and Pakistan) to higher than 50% in others (eg, Austria, Mexico, and Sweden). In the general population (comprising individuals with and without NAFLD), 12·1% (95% CI 9·3-15·6) of people had non-obese NAFLD and 5·1% (3·7-7·0) had lean NAFLD. The incidence of NAFLD in the non-obese population (without NAFLD at baseline) was 24·6 (95% CI 13·4-39·2) per 1000 person-years. Among people with non-obese or lean NALFD, 39·0% (95% CI 24·1-56·3) had non-alcoholic steatohepatitis, 29·2% (21·9-37·9) had significant fibrosis (stage ≥2), and 3·2% (1·5-5·7) had cirrhosis. Among the non-obese or lean NAFLD population, the incidence of all-cause mortality was 12·1 (95% CI 0·5-38·8) per 1000 person-years, that for liver-related mortality was 4·1 (1·9-7·1) per 1000 person-years, cardiovascular-related mortality was 4·0 (0·1-14·9) per 1000 person-years, new-onset diabetes was 12·6 (8·0-18·3) per 1000 person-years, new-onset cardiovascular disease was 18·7 (9·2-31·2) per 1000 person-years, and new-onset hypertension was 56·1 (38·5-77·0) per 1000 person-years. Most analyses were characterised by high heterogeneity.

INTERPRETATION

Overall, around 40% of the global NAFLD population was classified as non-obese and almost a fifth was lean. Both non-obese and lean groups had substantial long-term liver and non-liver comorbidities. These findings suggest that obesity should not be the sole criterion for NAFLD screening. Moreover, clinical trials of treatments for NAFLD should include participants across all body-mass index ranges.

FUNDING

None.

Prevalence and Profile of Nonalcoholic Fatty Liver Disease in Lean Adults: Systematic Review and Meta-Analysis

Data on prevalence and profile of nonalcoholic fatty liver disease (NAFLD) among individuals who are lean (normal body mass index) is unclear. Published data from studies comparing lean with obese NAFLD or with healthy subjects on prevalence, comorbidities, liver chemistry and histology, and metabolic/inflammatory markers were analyzed. Data were reported as odds ratio and 95% confidence interval for categorical variables and difference of means for continuous variables. Analysis of 53 studies on 65,029 subjects with NAFLD (38,084 lean) and 249,544 healthy subjects showed a prevalence of lean NAFLD at 11.2% in the general population. Among individuals with NAFLD, the prevalence of lean NAFLD was 25.3%. Lean NAFLD versus healthy subjects had higher odds for abnormalities on metabolic profile, including metabolic syndrome and its components, renal and liver function, and patatin-like phospholipase domain-containing protein 3 (PNPLA3) G allele; and inflammatory profile, including uric acid and C-reactive protein. The abnormalities were less severe among lean versus obese NAFLD on metabolic syndrome with its components, renal and liver chemistry, liver stiffness measurement, PNPLA3 and transmembrane 6 superfamily member 2 polymorphisms, and uric acid levels as markers of inflammation. Lean NAFLD had less severe histologic findings, including hepatocyte ballooning, lobular inflammation, NAFLD activity score, and fibrosis stage. Limited data also showed worse outcomes between obese versus lean NAFLD. Conclusion: Lean NAFLD is a distinct entity with metabolic, biochemical, and inflammatory abnormalities compared to healthy subjects and a more favorable profile, including liver histology of steatohepatitis and fibrosis stage, compared to obese NAFLD. We suggest that prospective multicenter studies examine long-term hepatic and extrahepatic outcomes in individuals with lean NAFLD.

Epidemiology of nonalcoholic fatty liver disease in non-obese populations: Meta-analytic assessment of its prevalence, genetic, metabolic, and histological profiles

OBJECTIVE

As a subgroup of nonalcoholic fatty liver disease (NAFLD), patients with non-obese NAFLD may also have an increased risk of adverse hepatic and metabolic outcomes. We aimed to estimate the prevalence and incidence of non-obese NAFLD and to describe its clinical characteristics in this systematic review and meta-analysis.

METHODS

We performed a systematic search of 1235 citations published up to Mar 2020. Meta-analyses, stratified analyses and meta-regression were all performed.

RESULTS

Of the 46 studies included, 28 cross-sectional and longitudinal studies of 155 846 non-obese participants reported a pooled NAFLD prevalence of 14.5% (95% confidence interval [CI] 12.3%-17.1%). A multivariate meta-regression analysis showed the trend that the prevalence varied by their geographical location. Further stratified analyses showed that NAFLD was relatively prevalent among people aged ≥45 years (16.2%; 95% CI 10.8-23.4) and those in South America (25.7%; 95% CI 24.4-27.0). The PNPLA3 rs738409 gene polymorphism was more frequently observed in non-obese NAFLD than in both obese NAFLD and non-obese controls, while the metabolic profiles of non-obese NAFLD were less severe than those of the obese NAFLD group. Patients with non-obese NAFLD had 4.81-fold and 5.43-fold higher risk of diabetes mellitus and metabolic syndrome, respectively, than the non-obese controls.

CONCLUSIONS

Non-obese NAFLD is common, particularly in South America and among people aged ≥45 years. Metabolic diseases and PNPLA3 rs738409 gene polymorphism are more frequent in the non-obese NAFLD group than in non-obese controls.

Epidemiology of non-alcoholic fatty liver disease and non-alcoholic steatohepatitis in Japan: A focused literature review

Non‐alcoholic fatty liver disease (NAFLD) and non‐alcoholic steatohepatitis (NASH) represent a growing unmet medical need and an increasingly prevalent cause of cirrhosis, hepatocellular carcinoma (HCC), and death in Japan. The aim of this review was to characterize the epidemiology of NAFLD and NASH in Japan. An English and Japanese literature search was conducted in PubMed, Embase, and ICHUSHI Web, identifying 6553 studies, 67 of which were included. Prevalence of NAFLD in the Japanese population rose from the early 1990s (12.6–12.9%) to the early 2000s (24.6–34.7% of the population). Japanese NASH prevalence is estimated to be 1.9–2.7%. NAFLD and NASH are more common among males than females; however, females experience more severe disease than males. While obese patients had higher prevalence of NAFLD/NASH, nonobese individuals (body mass index [BMI] <25 kg/m²) consistently comprised 20% to >35% of NAFLD and NASH patients. The evidence shows that, despite obesity being linked with worse disease stages, “lean‐NASH” also plays an important role in NASH epidemiology. Besides obesity, diabetes and metabolic syndrome appeared to be reliably associated with disease severity. The prevalence of advanced fibrosis or cirrhotic disease was the highest in patients with NASH‐HCC (44–80% with stage F3/F4 disease), while 21–50% of patients with NASH had F3/F4 disease. NAFLD/NASH is common in the Japanese population, and the prevalence of these conditions has tripled in the last two decades. Furthermore, these NAFLD/NASH patients have a high comorbidity burden. Early and efficient identification of safe and effective treatments for NAFLD/NASH patients is urgently needed.

Association between body size-metabolic phenotype and nonalcoholic steatohepatitis and significant fibrosis

BACKGROUND AND AIMS

Body size-metabolic phenotype may help predict whether or not individuals with nonalcoholic fatty liver disease (NAFLD) develop advanced liver disease. We studied the association of body size-metabolic phenotype with nonalcoholic steatohepatitis (NASH) and significant fibrosis.

METHODS

Our cross-sectional study included 559 subjects (mean age of 53 years; women 51%) with biopsy-proven NAFLD. Clinical, genetic, and histological characteristic features of NAFLD were evaluated. The metabolically unhealthy phenotype was defined by the presence of two or more metabolic components, while body size was categorized based on body mass index: obese (≥ 25 kg/m2) or non-obese (< 25 kg/m2). Body size-metabolic phenotypes were divided into four study groups: (1) non-obese metabolic syndrome (MS)-, (2) non-obese MS+ , (3) obese MS-, and (4) obese MS+.

RESULTS

Obese MS- and non-obese MS+ groups demonstrated comparable levels of insulin resistance, adipose tissue insulin resistance indexes, and visceral adipose tissue (VAT) areas. The VAT area was significantly higher in the obese MS+ group versus obese MS- group. However, the VAT to subcutaneous adipose tissue (SAT) ratio was highest in the non-obese MS+ group. There was no difference in histology between the non-obese MS+, obese MS-, and obese MS+ groups. Multivariate analyses adjusted for age, sex, smoking status, PNPLA3, TM6SF2, and VAT/SAT areas demonstrated an independent and dose-dependent relationship between the body size-metabolic phenotype and NASH or significant fibrosis.

CONCLUSION

The non-obese MS+ group displayed similar degree of hepatic histological severity compared to their obese MS- counterparts. Metabolic milieu beyond obesity may play a pathogenic role in non-obese MS+ individuals who develop NASH with significant hepatic fibrosis.

CLINICAL TRIAL NUMBER

NCT02206841.

Nonalcoholic Fatty Liver Disease in Adults: Current Concepts in Etiology, Outcomes, and Management

Nonalcoholic fatty liver disease (NAFLD) is a spectrum of disease, extending from simple steatosis to inflammation and fibrosis with a significant risk for the development of cirrhosis. It is highly prevalent and is associated with significant adverse outcomes both through liver-specific morbidity and mortality but, perhaps more important, through adverse cardiovascular and metabolic outcomes. It is closely associated with type 2 diabetes and obesity, and both of these conditions drive progressive disease toward the more advanced stages. The mechanisms that govern hepatic lipid accumulation and the predisposition to inflammation and fibrosis are still not fully understood but reflect a complex interplay between metabolic target tissues including adipose and skeletal muscle, and immune and inflammatory cells. The ability to make an accurate assessment of disease stage (that relates to clinical outcome) can also be challenging. While liver biopsy is still regarded as the gold-standard investigative tool, there is an extensive literature on the search for novel noninvasive biomarkers and imaging modalities that aim to accurately reflect the stage of underlying disease. Finally, although no therapies are currently licensed for the treatment of NAFLD, there are interventions that appear to have proven efficacy in randomized controlled trials as well as an extensive emerging therapeutic landscape of new agents that target many of the fundamental pathophysiological processes that drive NAFLD. It is highly likely that over the next few years, new treatments with a specific license for the treatment of NAFLD will become available.

Non-alcoholic fatty liver disease in lean individuals

Non-alcoholic fatty liver disease (NAFLD) is a major cause of chronic liver disease, encompassing a spectrum from non-alcoholic fatty liver to non-alcoholic steatohepatitis, which can progress to cirrhosis. It has recently been recognised that NAFLD also occurs in individuals who are not obese, especially in Asian populations. In these patients, NAFLD manifests at lower overall body mass index thresholds in the presence of increased visceral adipose tissue. Currently, the principles of clinical management are similar to those in obese individuals, although, in specific regions and clinical situations, unique aetiologies of NAFLD must be treated specifically.

Alcoholic and non-alcoholic steatohepatitis: global perspective and emerging science

Alcohol and high-fat diet are two major risk factors responsible for metabolic diseases, which are manifested as steatohepatitis and liver cancer in the liver, and chronic pancreatitis and pancreatic adenocarcinoma (PDAC) in the pancreas. These metabolic diseases are becoming increasingly prevalent around the globe, and more importantly, their two major etiologies commonly coexist to precipitate the disease processes. To highlight the importance of these metabolic diseases, Japanese Society of Gastroenterology (JSGE) and National Institute on Alcoholism and Alcohol Abuse of National Institute of Health cosponsored the JSGE's 7th International Forum jointly held with the 12th International Symposium on ALPD and Cirrhosis. Toward the main theme of "Frontiers in ASH, NASH, NBNC-HCC and PDAC", this platform showcased presentations by 12 invited international and Japanese speakers on brain-gut-liver interactions, emerging mechanisms of ASH and NASH, metabolic reprogramming, and new therapeutic targets for cirrhosis, HCC, and PDAC. This editorial discusses the most recent data on global statistics on how alcohol and obesity impact health and longevity as a prelude to a brief summary of the symposium presentations and discussions, primarily focusing on the first two session themes.

Predictors of nonalcoholic steatohepatitis and significant fibrosis in non-obese nonalcoholic fatty liver disease

AIMS

We compared (a) demographic and clinical characteristics and (b) determinants of nonalcoholic steatohepatitis and significant fibrosis in non-obese and obese nonalcoholic fatty liver disease.

METHODS

A cross-sectional study of 664 Asian subjects (mean age 53.1 years; men 50.3%) with biopsy-proven nonalcoholic fatty liver disease and controls was conducted. Subjects were divided by their body mass index into obese (body mass index ≥25 kg/m2 ) and non-obese (body mass index <25 kg/m2 ).

RESULTS

Observations in subjects with non-obese nonalcoholic fatty liver disease were in between non-obese controls and subjects with obese nonalcoholic fatty liver disease for body mass index, sagittal abdominal diameter, aminotransferase levels, insulin resistance and abdominal visceral adipose tissue area. There was no significant difference in histology between non-obese and obese subjects with nonalcoholic fatty liver disease except for lower grade of hepatic steatosis in nonobese nonalcoholic fatty liver disease and higher severity of hepatic fibrosis in nonobese nonalcoholic steatohepatitis. Predictors of nonalcoholic steatohepatitis in nonobese subjects included females (odds ratio 2.49), higher alanine aminotransferase (odds ratio 1.03), lower high-density lipoprotein cholesterol (odds ratio 0.96), higher prevalence of diabetes (odds ratio 3.65) and higher visceral adipose tissue area (odds ratio 1.63 per standard deviation increase of visceral adipose tissue area) while age (odds ratio 1.04), higher aspartate aminotransferase (odds ratio 1.02), diabetes (odds ratio 2.76) and higher visceral adipose tissue area (odds ratio 1.57 per standard deviation increase) were associated with significant fibrosis in the non-obese. Sagittal abdominal diameter was independently associated with nonalcoholic steatohepatitis or significant fibrosis among subjects with non-obese nonalcoholic fatty liver disease.

CONCLUSION

While there were a few phenotypic differences from obese subjects, non-obese subjects with nonalcoholic fatty liver disease displayed a similar severity of histological liver damage. Potential factor(s) beyond obesity may play a role as non-obese nonalcoholic fatty liver disease advances to more severe disease.

NAFLD and HIV: Do Sex, Race, and Ethnicity Explain HIV-Related Risk?

PURPOSE OF REVIEW

Here, we review the epidemiology, diagnosis, and management of non-alcoholic fatty liver disease (NAFLD) in the general population, discuss HIV-specific differences in NAFLD pathogenesis, and summarize what is known regarding differences in NAFLD by race/ethnicity and sex.

RECENT FINDINGS

The reported prevalence of NAFLD among people living with HIV varies by age, body mass index, comorbidity, and method of NAFLD diagnosis, but is generally thought to be greater among HIV-infected compared to HIV-uninfected populations. Minorities and women tend to experience poorer HIV treatment outcomes (Meditz et al. J Infect Dis. 203(4):442-51, 2011; Beer et al. Medicine (Baltimore). 95(13):e 3171, 2016; Gant et al. MMWR Morb Mortal Wkly Rep. 66(40):1065-72, 2017; Millett et al. Lancet. 380(9839):341-8, 2012; Wejnert et al. J Infect Dis. 213(5):776-83, 2016), and are at the greatest risk for significant weight gain with HIV treatment (Erlandson et al. Medicine (Baltimore). 95(46):e 5399, 2016). Thus, women and minorities living with HIV may be at a higher risk of developing NAFLD and progressive liver disease. Disparities in the diagnosis, progression, and prognosis of NAFLD and HIV-associated NAFLD may be, in part, explained by genetic and sex differences; however, data is limited.

Neonatal intake of oleanolic acid attenuates the subsequent development of high fructose diet-induced non-alcoholic fatty liver disease in rats

Dietary manipulations during the early postnatal period are associated with the development of metabolic disorders including non-alcoholic fatty liver disease (NAFLD) or long-term protection against metabolic dysfunction. We investigated the potential hepatoprotective effects of neonatal administration of oleanolic acid (OA), a phytochemical, on the subsequent development in adulthood, of dietary fructose-induced NAFLD. Male and female suckling rats (n=112) were gavaged with; distilled water (DW), OA (60 mg/kg), high fructose solution (HF; 20% w/v) and OA+HF (OAHF) for 7 days. The rats were weaned onto normal rat chow on day 21 up to day 55. From day 56, half of the rats in each treatment group were continued on plain water or HF as drinking fluid for 8 weeks. Hepatic lipid accumulation and hepatic histomorphometry were then determined. Fructose consumption in adulthood following neonatal fructose intake (HF+F) caused a 47-49% increase in hepatic lipid content of both male and female rats (P<0.05). However, fructose administered in adulthood only, caused a significant increase (P<0.05) in liver lipid content in females only. NAFLD activity scores for inflammation and steatosis were higher in the fructose-fed rats compared with other groups (P<0.05). Steatosis, low-grade inflammation and fibrosis were observed in rats that received HF+F. NAFLD area fraction for fibrosis was three times higher in rats that received fructose neonatally and in adulthood compared with the rats in the negative control group (P<0.05). Treatment with OA during a critical window of developmental plasticity in rats prevented the development of fructose-induced NAFLD.

The relationship between obesity and the severity of non-alcoholic fatty liver disease: systematic review and meta-analysis

A number of researches have explored the association between obesity and nonalcoholic fatty liver disease (NAFLD) liver function, histopathology, complications, genetic factors and prognosis, but the results were conflicting and inconclusive. Areas covered: In this meta-analysis, the liver function, histopathology, metabolic complications, patatin-like phospholipase domain-containing protein 3 (PNPLA3) genetic polymorphism and prognosis were compared between non-obese and obese NAFLD. Pubmed, EMBASE, Cochrane databases were searched to identify eligible studies. The odds ratio (OR) or standardized mean difference (SMD) with 95% confidence intervals (CI) were pooled using fixed- or random-effects models. Expert commentary: This meta-analysis indicated that for NAFLD patients, obesity (according to ethnic-specific BMI cut-off points to define obesity) could predict a worse long-term prognosis. However, obesity may not be an independent factor for the development of NASH or advanced fibrosis in NAFLD patients and NAFLD should be considered as potential population for pharmacologic treatment regardless of obesity. In addition, PNPLA3 rs738409 may be more relevant to the progression of non-obese NAFLD when compared to obese NAFLD. Importantly, large-sample, long-term follow-up cohort studies based on liver biopsy are highly needed due to limited liver pathology and long-term follow-up data at present.