Effect of black garlic on visceral fat, oxidative stress and insulin resistance in nonalcoholic fatty liver disease rats

Abstract

Purpose This paper aims to determine the effect of black garlic (BG) on visceral fat, oxidative stress and insulin resistance (IR) compared with metformin and vitamin E in nonalcoholic fatty liver disease (NAFLD) rats. Design/methodology/approach A randomized post-test only design with control group was used in this study. Rats were given high-fat fructose diet enriched with 1.25% cholesterol and 0.5% cholic acid for eight weeks to induce NALFD condition. The administration of BG dose of 450 mg/200 gBW, 900 mg/200 gBW and 1350 mg/200 gBW with a comparative control of 45 mg/200 gBW of metformin and vitamin E of 9 IU/200 gBW were given for four weeks via oral gavage to reduce visceral fat, oxidative stress and improve IR. Statistical analyses were performed to examine differences between groups with one-way analysis of variance and nonparametrics test. Findings Rats given with three different doses of BG for four weeks did not reduce body weight from 244 ± 4.4 to 284 ± 4.6 g, 242 ± 2.5 to 272 ± 3.1 g and 240 ± 2.4 to 270 ± 3.6 g, respectively, but significantly reduced visceral fat (p = 0.001) on BG groups with 3.7 ± 1.3, 2.7 ± 0.7 and 1.8 ± 0.6 g, respectively. BG improved oxidative stress (p = 0.001) with malondialdehyde level 5.1 ± 0.2, 3.0 ± 0.06 and 2.3 ± 0.06 ng/mL, respectively, but did not better than vitamin E group 1 ± 0.03 ng/mL. Significant (p = 0.001) improvement on insulin resistance with homeostatic model assessment IR in BG groups were 5.3 ± 0.1, 4.4 ± 0.1 and 4 ± 0.1, respectively, but not as good as metformin group 3.7 ± 0.1. Research limitations/implications Based on the experiment, there are several limitations including small sample size, performed on animal models in a relatively short time, did not examine organosulfurs compound (OSC) content of BG specifically and OSC affects metabolism in NAFLD remains unclear and will require further investigation. Practical implications BG is a functional food made from heated fresh garlic owing to the Maillard reaction and the organosulfur compounds as antioxidants. The higher the dose of BG, the greater the improvement in visceral fat, oxidative stress and IR in model NAFLD rats. Social implications NAFLD is a liver disorder caused by excessive fat and energy intake, the treatment strategies among others through diet modification. Originality/value In model NAFLD rats, BG administration improved NALFD markers but did not better rather than the metformin and vitamin E result.