From a nutritional perspective, starches can be classified according to their digestive fate in the gastrointestinal tract. Starches can be fully digestible in the small intestine (either rapidly digested or slowly digested) or indigestible (resistant). Depending upon food consumption practices and individual gastrointestinal processes, it is possible that some digestible starch may
Table 8.1 Known effects of RS on parameters relevant to weight management
Resistant to digestion - does not contribute to available glucose Decreased caloric contribution compared with digestible starch Decreased macronutrient utilization Decreased body fat accumulation Decreased adipocyte volume
Increased lipid oxidation at the expense of carbohydrate oxidation
Decreased lipid production (lipogenesis)
Increased insulin sensitivity
Decreased glucose response
Decreased insulin response
Possible contribution to satiety actually pass through the small intestine undigested and contribute to the amount of RS.
Following the discovery that some starch resisted digestion, RS became the subject of widespread attention by a collaborative group of European researchers between 1990 and 1994, known collectively as EURESTA -European FLAIR-Concerted Action on the 'Physiological implication of the consumption of resistant starch in man'. It involved 36 groups from 10 countries, and was organized into the following four areas: (1) definition and analysis of RS; (2) RS production and technological impact; (3) physiological effects of RS, principally as they relate to the upper and lower gastrointestinal tract; and (4) the energy contribution of RS (Brown et al., 2001). Although an officially recognized method to quantify RS did not emerge from this extensive program, it did provide a significant base for subsequent RS research.
The EURESTA group proposed a definition for RS, namely: 'Resistant starch is the sum of starch and products of starch degradation not absorbed in the small intestine of healthy individuals' (Asp, 1992). Although this is not a current regulatory definition, it has become widely accepted. The definition proposed by EURESTA is a physiological and not a chemical definition. As a consequence any measurement of RS must reflect how much starch is digested and what occurs to starch in the body. RS is comprised of many chemically and physically distinct starch and starch-derived materials.
RS is best measured in vivo in humans as the starch excreted at the terminal ileum of ileostomate subjects, as this directly accounts for individual variation in the gastrointestinal tract management of starches. However, this remains an estimate because ileostomates are not intact healthy individuals. The in vitro quantification of the RS content of foods and ingredients employs enzyme-based methods that simulate the gastrointestinal tract, such as that recommended by the Association of Official Analytical Chemists (AOAC) which make reference to RS, dietary fiber and resistant maltodextrins.
Definitions of dietary fiber have recently been expanded by several groups to recognize a larger range of dietary components that demonstrate appropriate and defined physiological behaviors. RS has been considered a part of dietary fiber according to the definitions proposed by the Institute of Medicine of the National Academies in the USA (IOM, 2002) and the American Association of Cereal Chemists (AACC, 2001) according to the specific physiological effects described. The Codex Alimentarius Commission (FAO/WHO, 2005) has also proposed a definition for dietary fiber that lists physiological effects, and if approved would also recognize RS.
Dietary fiber represents a broad range of compounds, based on structure and chemistry, and each component of dietary fiber should be individually assessed for its role in the formulation of foods. RS has it own unique profile of physiological and food engineering benefits that often recommend its use when compared with other fibers. Typically RS can be used to increase the dietary fiber of foods with minimal changes to their appearance or organoleptic properties.
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