**1. Introduction**

Dietary fiber include fibers from natural sources (such as fruits, vegetables, and wholegrain cereals), fibers that are extracted or obtained by other means from food material, and synthetic carbohydrate polymers, that have been shown to possess physiological health benefits [1, 2]. Dietary fiber can be classified analytically as soluble and insoluble based on their solubility in water, but can also be characterized as viscous or non-viscous and fermentable or non-fermentable depending upon the physiological characteristics the fiber might have [2]. Insoluble dietary fiber includes cellulose, part of hemicellulose, and lignin, whereas soluble fibers include components such as pectin, some hemicelluloses, lignin, gums and mucilage [2, 3]. Whilst there have been difficulties in achieving a global definition for dietary fiber, it is now generally accepted that dietary fiber can be defined as carbohydrate polymers with a degree of polymerization of 3 or more monomeric units which are not hydrolysed in the small intestine by the endogenous enzymes [4]. As fiber is resistant to digestion and absorption in the human small intestine, it enters the colon where it can be partially or completely fermented [5].

Polydextrose is a polysaccharide produced by the random polymerization of glucose in the presence of sorbitol and a suitable acid catalyst, at a high temperature and under partial vacuum [6]. Polydextrose is composed of a mixture of glucose oligomers, with an average degree of polymerization ~12, but ranging from residual monomer to dp >100 [6, 7]. It is a branched molecule, and contains all different combinations of α- and β-linked 12, 13, 14 and 16 glycosidic linkages (Figure 1) [7, 8]. As polydextrose is only partially digested during gastrointestinal transit, it acts as a substrate for saccharolytic fermentation throughout the colon, even to the distal parts [9-12]. Polydextrose has a low caloric value: about 1 kcal/g, and it is widely used as a bulking agent and to replace the structure and texture of sucrose in low-calorie products by the food industry in confectionery applications, in pastry and bread, in dairy products, meat products, pasta and noodles, and in beverages [7, 13]. Polydextrose is widely accepted as a soluble fiber and has scientifically substantiated fiber characteristics, including increase in stool weight, decreased transit time, improved

© 2013 Putaala, licensee InTech. This is an open access chapter distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2013 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

stool consistency and ease of defecation, and reduced fecal pH [7]. It is safe to use, and well tolerated, with a mean laxative threshold of 90 g/day, or 50 g as a single bolus dose [14-16].

Polydextrose in Lipid Metabolism 235

**2. Polydextrose studies in animals, human and** *in vitro***: Contribution of** 

Polydextrose is a fermentable non-viscous fiber, and has been shown to exhibit lipid metabolism regulating effects [5]. Typically these effects have been associated with two physiochemical properties of soluble fibers: viscosity and fermentability. Viscous soluble fibers may work by slowing down gastric emptying and prevention of bile salt reabsorption which would increase the secretion of bile acids and neutral sterols into feces and interruption of the enterohepatic circulation of bile acids [35, 36]. Soluble fiber can also decrease intestinal cholesterol absorption by affecting micelle formation and mobility [37, 38], and reduce glycemic response leading to lower insulin stimulation and hepatic cholesterol synthesis [39]. Fibers can also promote satiety [40]. Additionally, colonic fermentation products of these fibers, short chain fatty acids (SCFAs), mainly propionate, have been shown to inhibit hepatic fatty acid synthesis [41]. Polydextrose has been reported to confer lipid modulating effects in human clinical intervention studies, as well as in animal studies. However, some of the characteristics of polydextrose are different to other soluble

fibers, such as low viscosity, and sustained fermentation throughout the colon [11].

The ability of polydextrose to modulate triglycerides, total, LDL, and HDL cholesterol has been studied in animals both in normal diets without additional lipid load or in diets in which lipids have been included as part of the normal diet. There is a clear difference between the types of studies, as the two studies without lipid load have not shown any effect on the blood lipid values. In a 6-week feeding study in normal rats with 5 % (w/w) inclusion of polydextrose no change in plasma triglycerides, total cholesterol, and HDL cholesterol or liver cholesterol, triglycerides and phospholipids was observed [42]. Another, 15-day feeding trial with rats, did not show differences in serum total and free cholesterol, triacylglycerols, and phospholipids even though 3 % polydextrose was administered

However, in two other rat feeding studies in which polydextrose was accompanied with a lipid load, reduced lipid levels were reported. In one study rats were given two different dosages of corn oil, 10 % and 20 %, to represent a moderate or high fat diet, for 8 weeks, with or without 5 % polydextrose [44]. Rats in the polydextrose group showed decreased serum triglycerides as compared to a guar gum control in the high-fat diet, and increased levels of serum HDL cholesterol both in the moderate fat and high fat diet [44]. Serum total lipids and cholesterol remained at the level of the control [44]. One study has been done with gerbils: in the 4-week study the gerbils were fed with 0.15 % cholesterol with 30 % of the energy coming from fat and with inclusion of 6 % polydextrose [45]. Both liver and plasma total cholesterol as well as free and esterified cholesterol from liver decreased in the polydextrose group [45]. The effect was presumed by the authors to be related to the reduction of VLDL and LDL, since no change in HDL was observed [45]. In the same gerbil study, it was additionally investigated whether polydextrose can remove cholesterol from

**polydextrose in lipid metabolism** 

**2.1. Polydextrose studies in animals** 

together with 3 % pectin or 3 % cellulose [43].

**Figure 1.** Structure for the polydextrose. The letter R can be either hydrogen (H), sorbitol, sorbitol bridge, of more polydextrose. Polydextrose has highly branched complex three-dimensional structure with all different combinations of α- and β-linked 12, 13, 14 and 16 glycosidic linkages.

Several beneficial effects have been linked to the consumption of polydextrose. Consumption of polydextrose promotes the growth of beneficial bifidobacteria and lactobacilli while preventing the growth of harmful ones, such as clostridia [17, 18]. It has been suggested to possess anti-inflammatory actions and to improve the signs of osteoarthritis in canines [19], to increase IgA amount in the rat cecum [20], to reduce cyclooxygenase 2 expression in pigs distal colon, and to reduce lesions in rat colitis model [21]. Furthermore, it has been suggested to improve the absorption of magnesium, calcium [22- 25] and iron [26].

Soluble fiber, both viscous (e.g. gums, pectin and β-glucan) and non-viscous (e.g. polydextrose, resistant maltodextrin and inulin), has been suggested to have beneficial metabolic advantages. These include increasing satiety and reduction of body weight, control of postprandial glycemic and insulin responses, and hypocholesterolemic effects on serum lipid parameters [5, 27]. The inverse relationship of higher HDL to coronary artery disease risk has been recognized and is evident across numerous populations, and the increment of its relative amount over LDL has been generally accepted as a hallmark of better cardiovascular health [28]. Soluble fiber has been associated inversely with serum total and LDL cholesterol, while HDL cholesterol concentration has been reported to either slightly decrease or remain unchanged [29, 30]. This effect has been attributed as an effect of soluble viscous fibers, as insoluble fibers do not appear to affect serum cholesterol concentrations [31, 32]. The ability of soluble fibers to reduce serum triglyceride levels is also controversial, as in some studies an inverse association has been suggested, while in many studies no effect has been observed [29, 33]. Soluble viscous fibers have a characteristic of being hypocholesterolemic, reducing serum cholesterol by about 5-10 % for a 5-10 g dose in subjects with hypercholesterolemia, whereas insoluble fibers have not shown this effect [34].
