High fiber and beta carotene from sweet potatoes and pumpkin improve insulin resistance by inhibition of sterol regulatory binding protein 1c in liver of hypertriglyceridemic rats

Abstract

BACKGROUND: High sterol regulatory binding protein 1c (SREBP-1c) gene expression increases triglyceride synthesis, which induces insulin resistance. Short-chain fatty acids (SCFAs) from fiber fermentation and beta carotene may inhibit SREBP-1c gene expression. AIM: The aim of this study was to evaluate the high fiber and beta carotene diet on improving insulin resistance in hypertriglyceridemia rats. METHODS: A total of 25 Wistar male rats were divided into five groups: (1) Normal control (NC); (2) hypertriglyceridemia control (HC); (3) hypertriglyceridemia rats with treatment 1 (HT1); (4) hypertriglyceridemia rats with treatment 2 (HT2); and (5) hypertriglyceridemia rats with treatment 1 (HT3). The HT1, HT2, and HT3 received fiber 1.0 g; 2.0 g; and 3.1 g and beta carotene 725.7 µg; 1451.5 µg; and 2177.2 µg per day, respectively, for 6 weeks. The HC received high fat and fructose diet and the NC received a standard diet. The levels of triglyceride were analyzed using the colorimetric method before and after treatment. At the end of the study, the expression of SREBP-1c was identified by a quantitative polymerase chain reaction. RESULTS: High fat and fructose diet increased the levels of triglyceride (36.53 ± 1.27 vs. 119.79 ± 7.73), but high fiber and beta carotene diet can reduce triglyceride levels in HT1 (94.58 ± 4.53 vs. 77.70 ± 7.97); HT2 (115.58 ± 4.76 vs. 66.90 ± 3.11); and HT3 (103.87 ± 7.47 vs. 62.06 ± 4.45). The decreased triglyceride levels were related to low SREBP-1c gene expression, especially in the liver. Low SREBP-1c gene expression was correlated with homeostatic model assessment of insulin resistance index with r = 0.414; p < 0.05 in the liver and r = 0.158; p > 0.05 in white adipose tissues. CONCLUSION: High fiber and beta carotene diet can improve insulin resistance through inhibition of SREBP-1c gene expression.