Background and aims The prevalence of non-alcoholic fatty liver disease has been alarmingly increased with no lines of effective treatment. Vanillic acid is a naturally occurring polyphenol with promising therapeutic effects. Exercise is well known to be an effective tool against obesity and its consequences. Thus, we aim to study the effect of vanillic acid alone and along with exercise on fatty liver induced by a high-fat diet in a rat model and to investigate possible novel mechanisms involved in their action. Methods In this study, 40 male rats were divided equally into five groups: control (standard chow diet), HFD (high-fat diet), HFD+VA (HFD+ vanillic acid (50 mg/kg/day orally), HFD+EX (HFD+ swimming exercise 5 days/week), HFD+VA+EX (HFD+ vanillic acid+ swimming exercise) for eight weeks. Results Body mass, liver weight, liver enzymes, cholesterol, and triglycerides were significantly decreased in the combined VA+EX group, with marked improvement in hyperglycemia, hyperinsulinemia, and consequently HOMA-IR index compared to the HFD group. These improvements were also reflected in the pathological view. VA and swimming, either solely or in combination, markedly increased hepatic and circulating fibroblast growth factor 21. Additionally, VA and swimming increased the immunohistochemical expression of the autophagosomal marker LC3 and decreased the expression of P62, which is selectively degraded during autophagy. Conclusions These results suggest the hepatoprotective effect of VA and swimming exercise against fatty liver and the involvement of FGF21 and autophagy in their effect.

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