Analyzing and evaluating the prevalence and metabolic profile of lean NAFLD compared to obese NAFLD: a systemic review and meta-analysis

Background: Non-alcoholic fatty liver disease (NAFLD) is a common liver condition affecting 25%-40% of the worldwide population. NAFLD is traditionally related to obesity and metabolic disorders. NAFLD can also affect non-obese individuals, termed "lean NAFLD" (LN), who exhibit a paradoxical combination of physical leanness and metabolic obesity. Factors contributing to LN remain unclear, necessitating further research. This analysis aims to understand LN's prevalence and metabolic characteristics compared to obese NAFLD (ON) populations. Methods: This meta-analysis searched various databases until August 1, 2023. Inclusion criteria involved observational studies comparing LN with overweight/obese NAFLD. Data extraction included baseline characteristics, disease occurrence, metabolic profile, and clinical parameters-statistical analysis employed calculating risk ratios (RR) and standard mean differences. Results: Twenty-five studies were analyzed. LN is associated with lower prevalence in both NAFLD (RR 0.27, 95% confidence interval (CI) 0.14-0.52, p = <0.0001) and total (RR 0.27, 95% CI 0.15-0.51, p < 0.0001) population. LN had lower diabetes mellitus (RR 0.78, 95% CI 0.71-0.87, p < 0.00001), dyslipidemia (RR 0.87, 95% CI 0.79-0.95, p = 0.002), hypertension (RR 0.80, 95% CI 0.74-0.87, p < 0.00001), and metabolic syndrome (RR 0.45, 95% CI 0.31-0.64, p < 0.00001) compared to those with ON. The LN group's lipid profile, blood pressure, and other clinical parameters were favorable compared to ON. Conclusion: The prevalence of NAFLD among lean and non-lean individuals varies by region. Our analysis revealed that LN is associated with lower metabolic diseases, fasting blood sugar, blood pressure, and a more favorable lipid profile compared to ON. Plain language summary NAFLD prevalence and its characteristics among obese vs lean population Non-alcoholic fatty Liver Disease (NAFLD) is a prevalent liver condition affecting a substantial portion of the global population, commonly linked to obesity and metabolic disorders. However, a subset of individuals with NAFLD, termed "lean NAFLD" (LN), challenges the conventional association by presenting with physical leanness despite metabolic obesity. The factors contributing to this condition are not well understood, prompting this meta-analysis to explore the prevalence and metabolic characteristics of LN compared to obese NAFLD (ON) populations. The study, conducted through August 1st, 2023, analyzed 25 studies meeting inclusion criteria, which involved observational studies comparing LN with Overweight/Obese NAFLD. Data extraction included baseline characteristics, disease occurrence, metabolic profiles, and clinical parameters. Statistical analysis utilized risk ratios (RR) and standard mean differences. The results indicated that LN is associated with a significantly lower prevalence in both the NAFLD and general populations. LN demonstrated lower occurrences of diabetes (DM), dyslipidemia, hypertension, and metabolic syndrome compared to ON. Additionally, the LN group exhibited a more favorable lipid profile, blood pressure, and other clinical parameters in comparison to the ON group. In conclusion, the prevalence of NAFLD varies among lean and non-lean individuals across different regions. The meta-analysis revealed that LN is linked to a lower occurrence of metabolic diseases, lower fasting blood sugar levels, lower blood pressure, and a more favorable lipid profile compared to those with ON. These findings contribute valuable insights into the distinct metabolic characteristics of LN, shedding light on potential avenues for further research and clinical considerations in the understanding and management of NAFLD.