Appetite 56 (2011) 65–70
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Research report
Dietary fibres in the regulation of appetite and food intake. Importance of viscosity Mette Kristensen *, Morten Georg Jensen Department of Human Nutrition, Faculty of Life Sciences, University of Copenhagen, Rolighedsvej 30, DK-1958 Frederiksberg C, Denmark
A R T I C L E I N F O
A B S T R A C T
Article history: Received 22 July 2010 Accepted 19 November 2010 Available online 27 November 2010
Dietary fibres have many functions in the diet, one of which may be to promote control of energy intake and reduce the risk of developing obesity. This is linked to the unique physico-chemical properties of dietary fibres which aid early signalling of satiation and prolonged or enhanced sensation of satiety. Particularly the ability of some dietary fibres to increase viscosity of intestinal contents offers numerous opportunities to affect appetite regulation. Few papers on the satiating effect of dietary fibres include information on the physico-chemical characteristics of the dietary fibres being tested, including molecular weight and viscosity. For viscosity to serve as a proxy for soluble dietary fibres it is essential to have an understanding of individual dietary fibre viscosity characteristics. The goal of this paper is to provide a brief overview on the role of dietary fibres in appetite regulation highlighting the importance of viscosity. ß 2010 Elsevier Ltd. All rights reserved.
Keywords: Dietary fibres Viscosity Appetite regulation Obesity Energy intake
Introduction The role of dietary fibres in health and disease has become clearer in some cases, but still generates controversy in others. Many observational studies link high intakes of dietary fibre with reduced risk of cardiovascular disease (Jacobs, Meyer, Kushi, & Fulsom, 1998; Liu et al., 1999; McKeown, Meigs, Liu, Wilson, & Jacques, 2002; Sahyoun, Jacques, Zhang, Juan, & McKeown, 2006), incidence of type 2 diabetes (Esmaillzadeh, Mirmiran, & Azizi, 2005; McKeown et al., 2002; Montonen, Knekt, Jarvinen, Aromaa, & Reunanen, 2003; Schulze et al., 2007) and mortality (Jacobs, Andersen, & Blomhoff, 2007; Sahyoun, Jacques, Zhang, Juan, & McKeown, 2006), whereas the link to risk for developing different types of cancers is less consistent (Position of the American Dietetic Association, 2008). In recent years, dietary fibres have received increased attention for their potential role in weight regulation, and high intakes have been associated with a smaller weight gain in prospective observational studies (Bazzano et al., 2005; Koh-Banerjee et al., 2004; Liu et al., 2003). Trowell (1972) defined dietary fibres as the remnants of edible plant cell polysaccharides, lignin and associated substances which escape hydrolytic enzymatic digestion in the upper gastrointestinal tract. However, no universally accepted definition exists to date although a Codex definition of dietary fibres was agreed upon in 2009 which defines dietary fibres as ‘‘carbohydrate polymers with
* Corresponding author. E-mail address:
[email protected] (M. Kristensen). 0195-6663/$ – see front matter ß 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.appet.2010.11.147
10 or more monomeric units which are not hydrolysed by the endogenous enzymes in the small intestine of humans’’ (Codex Alimentarius Commision, 2009). This, along with many other dietary fibre definitions, is linked to analytical criteria which are good for labelling purposes (particularly solubility in water) but not as informative as for example viscosity and fermentability, as these are physicochemical properties which may affect gastrointestinal function. Research has been conducted to address the effects of viscous dietary fibres on physiological responses, but little data is provided on physico-chemical characteristics of individual dietary fibres used in the different intervention studies. Also, some limitations in the use of these characteristics when trying to predict the physiological response of dietary fibres may be the lack of established correlations between standardised in vitro and in vivo measurements. For viscosity to serve as a proxy for soluble dietary fibres it is essential to have an understanding of individual dietary fibre viscosity characteristics. The purpose of this paper is to discuss the importance of viscosity when considering the satiating effect of dietary fibres. Viscosity of solutions and gastrointestinal digesta Viscous dietary fibres induce thickening when mixed with liquids, and include many soluble dietary fibres such as gums, pectins, sea weed alginates and b-glucans. The degree of thickening depends on a number of factors such as structure, chemical composition, concentration and molecular weight (MW) (Dikeman & Fahey, 2006; Dikeman, Murphy, & Fahey, 2006).
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Viscosity of dietary fibres in solution also depends on their rate of hydration. Vuksan et al. (2009) found that viscosity of three preload drinks with glucomannan, cellulose or a new viscous polysaccharide (NVP) were similarly low immediately after mixing (
