Our findings demonstrate that patients with NAFLD were much more likely having higher BMI than healthy subjects; that support the hypothesis of NAFLD determination by body composition. Studies showed the prevalence of NAFLD is different between lean and obese people. Previous reports found an association between being overweight or obese and a higher prevalence of NAFLD (Church T.S.2006) and morbid obesity is associated with a higher prevalence of NAFLD (9, 10).
Just as some publications have reported obesity is closely related to NAFLD; our findings support this that suggests BMI, as an indicator of obesity, has a direct relationship with NAFLD. We demonstrated that BMI is higher in NAFLD than non-NAFLD subjects (adjusted OR: 1.21; CI 95%: 1.12–1.32). These findings support the study of Liu et al. that noticed the participants with NAFLD had higher BMI (11). On the other hand, Stranges et al concluded that BMI was not a reliable indicator of fatty liver disease (12).
Although many studies demonstrate BMI and general obesity associated with NAFLD, the components of body mass have different effect on NAFLD. Body composition in many aspects affects NAFLD. One of the components of body mass is fat mass. It decelerates as PBF and BFM. Studies have found that the accumulation of abdominal fat was positively correlated with liver fat (13), and increased in liver fat caused enhanced risk of NAFLD. The liver is a key organ to carbohydrate and lipid metabolism (14), so free fatty acid (FFA) concentrations resulting from lipolysis of body fat might be significantly greater than arterial FFA concentrations. So, the liver might be exposed to greater amounts of FFA, leading to an increased risk of NAFLD (15).
Our data reveal that there were differences in components of body mass including BFM, PBF, TBW, SLM between patients with NAFLD and healthy subjects after adjusting for confounding factors. However, we did adjust for several potential confounding factors such as gender, age, marital status, education, smoking, alcohol consumption, and physical activity. Our results imply that higher PBF might be a predictor of increased NAFLD (adjusted OR: 1.10; CI 95%: 1.03–1.17). As well as PBF, BFM (Adjusted OR: 1.12; CI 95%: 1.06–1.17), was significantly higher in NAFLD patients than healthy subjects. These findings agree with a recent study by Bhatt et al that concluded the body composition was different in NAFLD and without NAFLD patients. They measured body fat percent, arm fat, leg fat, total lean mass, and trunk fat by using whole-body dual-energy X-ray absorptiometry scan (16). Lawlor suggests the association between total fat mass with NAFLD (1). These findings are similar to our results. Because the pathophysiological mechanisms underlying the relationship between NAFLD and fat distribution remain unknown, further research is still needed to assess the predictive ability of each body fat parameter in terms of detecting NAFLD.
While increased BMI and obesity (BMI ≥ 30 kg/m2) is the major risk factor for NAFLD, several studies have now reported an association between low skeletal muscle mass and NAFLD (1, 17). Sarcopenia, as loss of skeletal muscle mass, and NAFLD share similar pathophysiological mechanisms, and the relationship between Sarcopenia and NAFLD has been recently investigated. The results of Bhatt et al. study showed total skeletal mass (kg) was different in with or without NAFLD subjects (16).
Hong HC, 2014 found a significant inverse association between skeletal muscle mass and NAFLD. They calculated SMI by weight and arms and legs lean mass (17). Similarly, Kim HY from the fifth Korea national health and nutrition examination survey noticed that the SMI has a significant negative correlation with NAFLD in both genders (18).
Sarcopenia has been associated with severity of NAFLD in patients and increased the risk of NAFLD in the general population(19), so Kim et al suggested increases in relative skeletal muscle mass over time may lead to benefits either in the development of NAFLD or the resolution of existing NAFLD (20). On the other hand, some NAFLD patients with normal BMI were lean compared with obese NAFLD and healthy controls (21).
Whereas our data showed a positive correlation between NAFLD and LBM (adjusted OR: 1.14; CI 95%: 1.08–1.20) or SLM (adjusted OR: 1.15; CI 95%: 1.09–1.22). Because at the baseline of our study the mean of weight in case and control group were not matched, our findings showed the amount of LBM and SLM by Kg in NAFLD patients is more than control group and if the results declare in percent, it might be the current prelateship between LBM and SLM is reversed.
Besides the fact that NAFLD more often affects men than women(22), our results showed that the BMI, BFM, PBF, TBW, SLM in NAFLD males was higher than NAFLD females. Our study declares TBW (adjusted OR: 1.20; CI 95%: 1.12–1.29) is different between NAFLD patients and healthy individuals. Also, TBW is different between male and female with NAFLD. No, other study assessed this parameter for NAFLD patients.
Nevertheless, we must acknowledge that this study had some limitations. First, in this study, we just demonstrate the difference of body composition parameters especially PBF between NAFLD patients and healthy individuals and the trend of this difference was vague. Second, our findings are not generalizable to the population due to the diversity in socio-demographic variables. Further studies in larger and various populations are required to understand the relationships among body composition with the stage of NAFLD to validate our results. The strengths of this study is it is the first study to investigate whether the association between body composition parameters with NAFLD in Iranian population.