Non-alcoholic fatty liver disease (NAFLD) is defined as an exacerbation of the triglyceride content in hepatocytes (greater than 5% of liver weight) without excessive alcohol consumption . NAFLD is the most common type of chronic liver disease in the world which might result in simple steatosis, non-alcoholic steatohepatitis (NASH) and fibrosis. These complication can eventually progress to cirrhosis or liver carcinoma . The general prevalence of NAFLD, based on ultrasound screening, is estimated to be 20–30% . In Asia, it has been reported that 15 to 40% of population are affected . According to a meta-analysis, 32% of population in the Middle East and 34% in Iran suffer from this condition .
Although weight loss has been the most effective strategy to manage this condition [6,7,8], dieting for weight loss has had little success in obese people in the long run. Therefore, it is necessary to find complementary therapies to control this condition. The composition of gut microbiota has recently gained great attention in several chronic diseases including fatty liver. Gut microbiota seem to affect this condition through various pathways including increased ethanol production, increased lipopolysaccharide (LPS) release and activating inflammatory cytokines [9, 10]. Therefore, modification of gut microbiota through probiotics might be a new strategy for effective management of NAFLD [11,12,13]. Earlier studies have shown the efficacy of probiotic supplements in improving levels of liver enzymes [14,15,16,17], lipid profiles [14, 18], inflammatory factors [19,20,21], steatosis  and fibrosis . However, due to the high cost of supplements, low access and the possibility of inducing infection and inflammation by their high dosages in long time [14,15,16,17], taking probiotics in the context of foods might be a superior choice than supplements. Probiotic foods also contain other nutrients that can be effective in liver health. In addition, findings based on supplements of probiotics may not be generalizable to all patients because of their short-term high dosage use in clinical trials [22,23,24,25,26].
Despite several studies about the effect of probiotic supplements on liver health, limited investigations have assessed the effect of probiotic-enriched foods. In a clinical trial on 102 NAFLD patients, consumption of synbiotic yogurt for 24-week resulted in a significant reduction in liver enzymes and steatosis . Nabavi et al., in a study on 62 patients with NAFLD, administered probiotic yogurt containing Lactobacillus acidophilus and Bifidobacterium for 12 weeks and found a significant reduction in liver fat and enzymes [28, 29]. None of these studies have examined the effect of such interventions on liver fibrosis. In addition, both studies have used ultrasound, rather than fibroscan, to examine liver fat, which might be subject to errors due to subjective decisions. Also, as evidenced in the latest systematic review and meta-analysis, further studies are needed to investigate the effect of probiotics on liver fibrosis, and since studies on probiotic foods are limited. Therefore, the aim of this study was to evaluate the effect of probiotic yogurt consumption on liver enzymes, steatosis and liver fibrosis in patients with NAFLD.