In this cross-sectional survey, we explored the comprehensive relationship between anthropometric indices, metabolic indices and FL and found that these indices have regulation and prediction effect on FL with a very complex pattern. To be specific, we demonstrated that 1) AST/ALT had strongest negative association with FL prevalence, while had the lowest predictive value for FL; and that 2) WC possessed the highest ability on predicting FL among all these indices.
The association of obesity with FL has been established in multiple previous studies[11, 15, 27, 28]. Epidemiological studies propose a causative link between obesity and progressive liver disease in individuals[15, 28]. Obesity has been linked not only to initial stages of the disease, but also to its severity. The pathophysiology and clinical studies have shown that the progression of FL results from an imbalance between lipid uptake and lipid disposal and eventually causes oxidative stress and hepatocyte injury. Obesity can be expressed in clinical practice by several methods, including anthropometric and metabolic ways. Some studies thought that the visceral adiposity was the main adipose depot responsible for FL and was associated with FL in a dose-dependent manner in a cohort study. WC, WHR and BMI have been proved and used in many clinical trials as an indicator of the severity of fatty liver disease[19, 22]. BFM and VFA are often reported markers in athletes related articles or are used to explore the relationship between insulin resistance and excessive visceral fat accumulation[31, 32]. Additionally, elevated data strongly suggests that advanced blood lipids, blood pressure and blood sugar could also be lead to more severe histological changes and poorer clinical outcomes[14, 22, 33]. Once FL is established, insulin resistance can promote the progression to the more severe state of liver endangerment like non-alcoholic steatohepatitis. Although the relationship between these ten obesity related indexes (WC, WHR, BMI, BFM, VFA, TG/HDL, AST/ALT, SBP, DBP and FBG) and FL were analyzed separately in many articles, few articles put them together to evaluate. Our studies compared all these 10 obesity related indexes with FL and also stratified the data by gender, thus we are capable of determining which factors might be critical for the regulation and prediction of FL.
In our study, we found differences of these ten obesity related indexes in three groups after stratifying the data. Men had a similar prevalence of FL regardless of age, whereas in women the prevalence of FL increased steadily with age. As we all know that sex hormones play a central role in predisposing individuals to metabolic status. Loss of estrogen after menopause leads to extensive changes in the metabolic system, including an increase in visceral adiposity. Although FL is primarily a male disease, the alteration in sex hormone levels, specifically reduced estrogens and increased androgens during and after menopause, is an important factor in the emergence of FL for female subjects[34, 35].
In our studies, we found blood lipids, blood sugar, WC and liver inflammatory indicators showed significant correlation with FL, while AST/ALT had a strongest negative association with increased FL prevalence. As we know, liver inflammation is closely related to metabolic disorders because the liver plays a central role in metabolism of lipids and glucose. Obesity and inflammation exist in the same time in FL almost, successive stages in FL may be reflected by the accumulation of fat in hepatocytes and the onset of steatohepatitis. Although the etiology of FL is multifactorial, it is well accepted that inflammation is a central component of FL pathogenesis[36, 37]. This may explain why the AST/ALT has the maximum increase in our study. And it is also agree with current treatment measures on FL. Besides, we found WC have a strong association with FL compared with VFA. This is in consistent with the study by Church et al. who found that adjustment for VFA attenuated the direct association between waist circumference and FL.
We further identified AST/ALT had the lowest predictive value for FL, while WC showed a correspondingly higher ability on prediction in all these indices. Nowadays, the mechanisms of hepatic steatosis and steatohepatitis are being investigated extensively which are regulated by complex pathways[36, 39]. Although inflammation contribute greatly to FL, abdominal obesity remains the main manifestations for FL. Compared with inflammatory changes existed in many diseases, WC have been shown in many studies to be directly related to fatty liver and to be more specific for FL[40–42].
This study characterized and analyzed a comprehensive profile for FL related indices, especially different anthropometric and metabolic indices. These comprehensive correlation analyses can enhance our understanding of the mechanisms for hepatic steatosis and steatohepatitis and is also important for developing strategies for the prevention and treatment of FL. However, there are still some limitations. Firstly, our findings are based on a cross-sectional study, a large-scale cohort study is still necessary to build the definite causal relationship between these indices and FL. Secondly, the data of other confounders, such as, smoking and drinking status and exercise, were not included in this analysis because of the information default.
In summary, this is a comprehensive profile for FL related indices. We identified AST/ALT had a strongest negative association with increased FL prevalence, but had the lowest predictive value for FL. Meantime, WC showed a correspondingly higher ability on predicting FL in all these indices. Findings from our study could provide further theoretical evidence for the understanding of relevant mechanisms for hepatic steatosis and steatohepatitis, as well as for predicting the prevalence of FL.