NutritionEffect of cellulose, pectin and chromium(III) on lipid and carbohydrate metabolism in rats
Introduction
Chromium(III) is an essential trace mineral required for carbohydrate and lipid metabolism [1]. It works by enhancing the effect of insulin. Chromium, usually in the form of chromium(III) chloride, picolinate or propionate is a popular supplement among people with diabetes and those interested in losing weight [2]. Its effect on carbohydrate and lipid metabolism has been researched with mixed outcomes. Results demonstrating the ability of chromium to improve glucose and insulin tolerance and to reduce blood glucose and lipids have been reported previously in diabetic rats [3], [4], [5], [6]. A beneficial effect of chromium on glycemic control was found in most, but not all, of the clinical trials with diabetic patients [7], [8], [9], [10]. A review of the literature reveals that chromium supplementation had little, if any, effect on the lipid profile in type 2 diabetes patients [7], [8].
The mechanism of chromium action has not been definitively established. Data from an in vivo study suggest that chromium may directly affect insulin receptor and increase its tyrosine kinase activity [11]. Chromium may exhibit its insulin-sensitizing effect also by reducing the content and activity of the tyrosine phosphatase PTP-1B [12] and by stimulating the translocation of GLUT4 glucose transporter to the plasma membrane associated with decreased plasma membrane cholesterol [13].
A high dietary fiber intake is emphasized in the recommendations of most diabetes and nutritional associations. It is accepted that viscous, gel-forming, soluble fiber (i.e., pectin, β-glucan) reduce postprandial glucose response and plasma total and LDL cholesterol concentration [14]. Several prospective cohort studies indicate that the consumption of insoluble cereal fiber (about 70% of cellulose) and whole grains is associated with improved insulin sensitivity and reduced the risk of the development of type 2 diabetes mellitus [15], [16], [17]. The mechanisms involved in the favorable effect of dietary fiber on glucose metabolism appear to differ for soluble and insoluble fibers. Soluble fiber modulates postprandial glycemic responses by delayed gastric emptying and small bowel transit; moreover, by reduced glucose diffusion through the unstirred water layer and reduced accessibility of α-amylase to its substrates due to the increased viscosity of gut contents [18]. The main cholesterol-lowering mechanism of soluble fiber is related to the decrease of bile acid reabsorption in the intestine [19]. Short-chain fatty acids – products of colonic fermentation of soluble fiber may also exert beneficial effects on lipid and carbohydrate metabolism.
Chromium(III), pectin and cellulose are available as natural food sources or commercial supplements. Although the individual action of these supplements has been investigated, their interactive effects on lipid and carbohydrate metabolism are still unknown. Therefore, the present study was designed to evaluate the effects of cellulose, pectin, chromium and their combination on plasma and liver lipids and on the concentration of glycated hemoglobin, glucose and insulin in the blood of rats.
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Materials and methods
The study was performed on eighty Buffalo rats (the mean initial body-weight 120 ± 10 g) divided into 8 groups (of 10 animals each), and fed for 6 weeks the experimental diets: group 1 – control fiber-free diet (FF), group 2 – fiber free diet with chromium (FF + Cr), group 3 – diet with 5% of cellulose (CEL), group 4 – diet with 5% of cellulose and chromium (CEL + Cr), group 5 – diet with 5% of pectin (PEC), group 6 – diet with 5% of pectin and chromium (PEC + Cr), group 7 – diet with 2.5% of cellulose
Statistical analysis
Data were analyzed using Statistica program ver. 6. Group comparisons were conducted using Tukey's post hoc test and 2-way ANOVA with fiber and Cr as the main effects. A p value ≤ 0.05 was accepted as significant.
Results
The diet intake and body weight of the rats did not differ between the groups. Average diet intake was within the range of 14.6 ± 1.1 to 15.8 ± 1.3 g/day, and weight gains of 100 ± 16 to 119 ± 28 g.
The diet supplemented only with PEC significantly improved the concentration of plasma cholesterol according to Tukey's test and 2-way ANOVA, while the interactive effects of both supplements (fiber and chromium) were not found (Table 2). The concentration of HDL-cholesterol was significantly higher in groups
Discussion
The results of our experiment showing that neither cellulose nor pectin, nor chromium supplementation significantly affected average diet intake and body weight of rats are in agreement with the observations reported in the other studies, where diets were supplemented with 5% of cellulose [22], 7% of pectin [23] or with different forms of Cr(III) [3], [24]. Moreover, we have not observed an interactive effect of fiber and chromium on these parameters.
The lower concentration of the plasma total
Conclusions
In conclusion, the results of this study indicated that pectin in the diet of rats contributed to a significant reduction of plasma total cholesterol, and the combination of pectin and chromium led to a significant increase of plasma HDL cholesterol and a decrease of triglyceride content in the liver. Moreover, individual supplementation of chromium, pectin and cellulose may improve lipid metabolism by decreasing cholesterol content in the liver.
The obtained results point out that cellulose
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