Nomenclature Dilemma of Metabolic Associated Fatty Liver Disease (MAFLD): Considerable Proportions of MAFLD Are Metabolic Healthy

Metabolically Healthy Obesity and Metabolic Dysfunction-Associated Steatotic Liver Disease (MASLD): Navigating the Controversies in Disease Development and Progression

PURPOSE OF REVIEW

The natural course of metabolic dysfunction-associated steatotic liver disease (MASLD) in the population with metabolically healthy obesity (MHO) has not been adequately explored. In the present narrative review, we summarize the evidence regarding the association between MHO and MASLD prevalence, incidence and progression.

RECENT FINDINGS

Cross-sectional, population-based, cohort studies have shown an increased prevalence of hepatic steatosis and fibrosis in subjects with MHO compared with metabolically healthy non-obese individuals (MHNO). In large-scale longitudinal cohort studies among metabolically healthy subjects, increasing body mass index (BMI) has been found to be independently associated with an increased incidence of MASLD and progressive hepatic fibrosis over a mean follow-up period of 2.2-7.7 years. With regard to advanced MASLD, the prevalence of steatohepatitis and clinically significant liver fibrosis is lower in MHO compared with subjects with metabolically unhealthy obesity (MUO). The presence of MASLD has been proposed as a strong risk factor for metabolic health deterioration in MHO. Furthermore, subjects with MHO and MASLD display an elevated 10-year cardiovascular risk and a three-fold increased risk of incident diabetes compared with MHO without MASLD. MASLD may also predict the failure to convert from MUO to MHO after a weight loss intervention.

From NAFLD to MAFLD and MASLD: a tale of alcohol, stigma and metabolic dysfunction

Liver steatosis is a frequent finding in clinical practice and it is estimated to affect 30% of the general adult population worldwide. It became one of the leading causes of end-stage liver disease and hepatocellular carcinoma. From its first description, a diagnosis of nonalcoholic fatty liver disease (NAFLD) required the exclusion of excessive alcohol consumption and concomitant chronic liver diseases of different origins, making it a diagnosis of exclusion. In recent years, the need to stress the strict association between liver steatosis and metabolic dysfunction (i.e., insulin resistance, overweight/obesity, type 2 diabetes, and metabolic syndrome), as well as the desire to define a condition in a positive rather than negative way, led to new definitions and new diagnostic criteria. Metabolic dysfunction-associated fatty liver disease (MAFLD) was proposed by Eslam et al. in 2020. More recently, a Delphi consensus endorsed by several international hepatologic societies proposed a new terminology [metabolic dysfunction-associated steatotic liver disease (MASLD)] and a new set of diagnostic criteria. The MAFLD and MASLD definitions have a good degree of concordance. They mainly differ in the number of metabolic derangements needed to define “metabolic dysfunction” in normal-weight individuals and in alcohol consumption. Indeed, while MAFLD does not exclude patients with significant alcohol consumption, the recent Delphi consensus included the metabolic dysfunction and alcohol-related liver disease (MetALD) disease entity, a condition in which steatosis, metabolic dysfunction, and moderate alcohol intake coexist. In the present narrative review, we underline the strengths and possible limitations of each definition and summarize available evidence from epidemiologic studies evaluating the clinical usefulness of each set of diagnostic criteria.

The Global Epidemic of Metabolic Fatty Liver Disease

PURPOSE OF REVIEW

The objective of this manuscript is to examine the current literature on the epidemiology of metabolic dysfunction-associated steatotic liver disease (MASLD), its correlation with cardiovascular disease (CVD) outcomes, as well as to evaluate the update in nomenclature from non-alcoholic liver disease (NAFLD).

RECENT FINDINGS

The update of diagnostic criteria from NAFLD to MASLD reduces the stigma associated with alcohol consumption and poor health choices. It also shines a light on the crucial role of cardiometabolic risk factors in disease pathophysiology. The incidence and prevalence of MASLD are projected to increase significantly in the future as the population burden of cardiometabolic risk factors rises. MASLD is also a potent risk factor for developing CVD that should be tackled by using a multi-disciplinary team with a holistic approach. As the new nomenclature for metabolic liver disease is adopted on a global scale, more research is needed to investigate the applicability of findings from previous trials focusing on NAFLD. It is anticipated that the epidemic of MASLD will continue to increase globally, hence the urgent need for therapeutic approaches to reverse this trend.

A simpler definition of MAFLD precisely predicts incident metabolic diseases: a 7-year cohort study

BACKGROUND

Metabolic dysfunction-associated fatty liver disease (MAFLD) is a novel definition proposed in 2020 with a relatively complex set of criteria. Thus, simplified criteria that are more applicable are required. This study aimed to develop a simplified set of criteria for identifying MAFLD and predicting MAFLD-related metabolic diseases.

METHODS

We developed a simplified set of metabolic syndrome-based criteria for MAFLD, and compared the performance of the simplified criteria with that of the original criteria in predicting MAFLD-related metabolic diseases in a 7-year follow-up.

RESULTS

In the 7-year cohort, a total of 13,786 participants, including 3372 (24.5%) with fatty liver, were enrolled at baseline. Of the 3372 participants with fatty liver, 3199 (94.7%) met the MAFLD-original criteria, 2733 (81.0%) met the simplified criteria, and 164 (4.9%) were metabolic healthy and met neither of the criteria. During 13,612 person-years of follow-up, 431 (16.0%) fatty liver individuals newly developed T2DM, with an incidence rate of 31.7 per 1000 person-years. Participants who met the simplified criteria had a higher risk of incident T2DM than those who met the original criteria. Similar results were observed for incident hypertension, and incident carotid atherosclerotic plaque.

CONCLUSION

The MAFLD-simplified criteria are an optimized risk stratification tool for predicting metabolic diseases in fatty liver individuals.

The Spectrum and Impact of Metabolic Dysfunction in MAFLD: A Longitudinal Cohort Analysis of 32,683 Overweight and Obese Individuals

BACKGROUND

Metabolic associated fatty liver disease (MAFLD) was recently proposed as an alternative name change for better encapsulation of disease. However, there exists a spectrum of MAFLD where both metabolically healthy (MH) and metabolically unhealthy (MU) individuals are included. In view of limited evidence, we sought to examine the prevalence, clinical characteristics, and differences in outcomes of MH-MAFLD at the population level.

METHODS

Data were used from the United States National Health and Nutrition Examination Survey 1999 to 2018. Multivariate logistic regression analysis was used to obtain odds ratios for the estimation of events. Survival analysis was conducted with Cox regression and the Fine-Gray subdistribution model.

RESULTS

There were 32,683 overweight and obese individuals included in the analysis. In MAFLD patients, the prevalence of MH-MAFLD was 6.92% (95% confidence interval [CI], 6.58%-7.27%), and 93.08% (95% CI, 92.73%-93.42%) were considered as MU-MAFLD. Multivariate analysis found a significantly higher risk of MACE (odds ratio, 1.38; 95% CI, 1.28-1.49; P < .01), all-cause (hazard ratio, 1.24; 95% CI, 1.17-1.32; P < .01), cardiovascular disease (SHR, 1.20; 95% CI, 1.02-1.42; P = .03), and cancer mortality (SHR, 1.24; 95% CI, 1.07-1.44; P < .01) in MU-MAFLD relative to non-MAFLD. However, MH-MAFLD individuals were not associated with a statistically significant increased risk of these adverse outcomes compared with non-MAFLD. MU-MAFLD diabetics were also at a higher risk of adverse events compared with non-diabetics.

CONCLUSIONS

This study reports on the heterogeneity and spectrum of metabolic dysfunction that exists in overweight and obese MAFLD. Although MAFLD may potentially be advantageous in improving awareness and patient outcomes, there remains substantial heterogeneity within patients included in MAFLD on the basis of the underlying metabolic burden.

Impact of metabolic risk factors on hepatic and cardiac outcomes in patients with alcohol- and non-alcohol-related fatty liver disease

Background & Aims

Metabolic risk factors (MetRs) are associated with hepatic and cardiac outcomes in patients with fatty liver disease (FLD). We evaluated whether MetRs have different effects on alcoholic FLD (AFLD) and non-alcoholic FLD (NAFLD).

Methods

We used a standardised common data model to analyse data from seven university hospital databases between 2006 and 2015. MetRs included diabetes mellitus, hypertension, dyslipidaemia, and obesity. Follow-up data were analysed for the incidence of hepatic outcomes, cardiac outcomes, and death in patients with AFLD or NAFLD and based on MetRs within AFLD and NAFLD.

Results

Out of 3,069 and 17,067 patients with AFLD and NAFLD, respectively, 2,323 (75.7%) and 13,121 (76.9%) had one or more MetR, respectively. Patients with AFLD were at a higher risk of hepatic outcomes (adjusted risk ratio [aRR], 5.81) compared with those with NAFLD irrespective of MetR. The risk of cardiac outcomes in AFLD and NAFLD became similar with the increasing number of MetRs. Patients with NAFLD without MetRs demonstrated a lower risk of cardiac outcomes, but not hepatic outcomes, compared with those with MetRs (aRR, 0.66 and 0.61 for MetR ≥1 and MetR ≥2, respectively; p <0.05). In patients with AFLD, hepatic and cardiac outcomes were not associated with MetRs.

Conclusions

The clinical impact of MetRs in patients with FLD may differ between patients with AFLD and those with NAFLD.

Impact and Implications

With the increasing prevalence of fatty liver disease (FLD) and metabolic syndrome, the increase in associated complications, such as liver and heart diseases, has become an important social issue. Particularly in patients with FLD with excessive alcohol consumption, the incidence of liver and heart disease is pronounced because of the dominant effect of alcohol over the effects of other factors. Thus, appropriate screening and management of alcohol consumption in patients with FLD are vital.

Characteristics and long-term mortality of patients with non-MAFLD hepatic steatosis

BACKGROUND & AIMS

A cluster of hepatic steatosis without metabolic abnormalities has been excluded by the MAFLD definition, referred to as non-MAFLD steatosis. We aimed to characterize the non-MAFLD steatosis.

METHODS

We included 16,308 individuals from the UK Biobank who had magnetic resonance imaging-derived proton density fat fraction (MRI-PDFF) to describe the clinical and genetic features of non-MAFLD steatosis in a cross-sectional design, and 14,797 individuals of the NHANES III who underwent abdominal ultrasonography at baseline to assess the long-term mortality of non-MAFLD steatosis in a prospective cohort design.

RESULTS

Of 16,308 individuals in the UK Biobank, 2747 fatty liver disease (FLD) cases (2604 MAFLD and 143 non-MAFLD) and 3007 healthy controls (without metabolic dysfunctions) were identified. The mean PDFF (10.65 vs. 9.00) and the proportion of advanced fibrosis (fibrosis-4 index > 2.67, 1.27% vs. 1.40%) were comparable between MAFLD and non-MAFLD steatosis. Non-MAFLD steatosis has the highest minor allele frequency of PNPLA3 rs738409, TM6SF2 rs58542926, and GCKR rs1260326 in contrast to the other two groups. The genetic risk score calculated by PNPLA3, TM6SF2, and GCKR has a certain predictive ability for non-MAFLD steatosis (AUROC = 0.69). NHANES III population showed that compared to healthy individuals, the adjusted hazard ratio of non-MAFLD steatosis increased by 1.52 (95% confidence interval: 1.21-1.91) and 1.78 (95% confidence interval: 1.03-3.07) for all-cause and heart disease-related mortality, respectively.

CONCLUSIONS

Non-MAFLD steatosis has comparable degrees of hepatic steatosis and fibrosis to MAFLD and increases the risk of mortality. Genetic predisposition highly contributes to the risk of non-MAFLD steatosis.

Risk of subclinical atherosclerosis across metabolic transition in individuals with or without fatty liver disease: a prospective cohort study

BACKGROUND

Metabolic dysfunction is a major determinant in the progression of fatty liver disease. It is pivotal to evaluate the metabolic status and subsequent transition in fatty liver population and to identify the risk of subclinical atherosclerosis.

METHODS

The prospective cohort study included 6260 Chinese community residents during 2010-2015. Fatty liver was determined as hepatic steatosis (HS) by ultrasonography. Metabolic unhealthy (MU) status was defined as having diabetes and/or ≥ 2 metabolic risk factors. Participants were categorized into 4 groups according to the combination of metabolic healthy (MH)/MU and fatty liver status (MHNHS, MUNHS, MHHS and MUHS). Subclinical atherosclerosis was assessed by elevated brachial-ankle pulse wave velocity, pulse pressure and/or albuminuria.

RESULTS

31.3% of the participants had fatty liver disease and 76.9% were in MU status. During a 4.3-year follow-up, 24.2% of participants developed composite subclinical atherosclerosis. Multivariable adjusted odds ratios for composite subclinical atherosclerosis risk were (1.66 [1.30-2.13]) in MUNHS group and (2.57 [1.90-3.48]) in MUHS group. It seemed that participants with fatty liver disease were more prone to be remained in MU status (90.7% vs.50.8%) and less likely to regress to MH status (4.0% vs. 8.9%). Fatty liver participants progressed to (3.11 [1.23-7.92]) or maintained MU status (4.87 [3.25-7.31]) significantly impelled the development of the composite risk, while regressing to MH status (0.15 [0.04-0.64]) were more intended to mitigate the risk.

CONCLUSIONS

The current study emphasized the importance of assessing metabolic status and its dynamic changes, especially in the fatty liver population. Regressing from MU to MH status not only benefited the systematic metabolic profile but also ameliorated future cardiometabolic complications.

Metabolic dysfunction associated fatty liver disease: The new nomenclature and its impact

BACKGROUND

In 2020, an international expert panel proposed a new definition of fatty liver: Metabolic dysfunction-associated fatty liver disease (MAFLD). The MAFLD added the criteria for defining metabolic dysfunctions, which are high-risk factors for liver-related and cardiovascular events. Contrary to the non-alcoholic fatty liver disease (NAFLD) definition, it allows the coexistence of MAFLD and significant alcohol use in the same patient.

AIM

To review the existing data that evaluate the clinical profile and long-term outcome difference between the patients identified as MAFLD and NAFLD.

METHODS

Databases MEDLINE via PubMed and EMBASE were searched and relevant publications up to June 28, 2022 were assessed. Studies were included if they involved human participants diagnosed with MAFLD.

RESULTS

A total of 2324 records were reviewed, of which 1575 duplicate citations were removed. Of the 2324 records screened, 207 articles were excluded, and 542 articles were assessed for their eligibility, for which 511 were excluded. The remaining 31 articles were selected for review. MAFLD diagnostic criteria were able to identify more individuals with fatty liver. Studies have shown that patients included using the MAFLD criteria were associated with higher risks of hepatic fibrosis when compared to NAFLD. All-cause mortality, cardiovascular disease-related, and cancer-related mortality were shown to be higher in MAFLD patients. MAFLD patients also had higher baseline metabolic derangement, and risks of developing obesity, diabetes, and cardiovascular events. Of the 3 subtypes, diabetes mellitus has the strongest association with negative outcomes, followed by metabolic dysfunction and elevated body mass index. Within the subtypes of MAFLD, patients with more metabolic conditions at the time of diagnosis had worse hepatic and liver injury compared to those with a single metabolic condition.

CONCLUSION

MAFLD is a new definition of fatty liver disease that is gaining increasing acceptance. It is based on empirical clinical practice on positive inclusion of metabolic risk factors and recent evidence suggests that it helps to identify patients with higher risk for liver-related as well as cardiovascular events.