Of all dietary factors, high fat intake in a population has been suggested to be the main contributor to the increasing prevalence of obesity (Astrup & Raben, 1992; Golay & Bobbioni, 1997). However, studies of the US population over the last few decades have reported that, despite the steady increase in the prevalence of overweight and obesity, fat intake has actually fallen from 42 to 34% of total energy, whereas carbohydrate intake has increased (Allred, 1995; Nicklas, 1995). Brand-Miller et al. (2002) suggested that current dietary recommendations to increase the percentage of daily energy as carbohydrate may be counterproductive to weight control, as many high-carbohydrate, low-fat diets markedly increase postprandial hyperglycaemia and hyperinsulinaemia. Not only the amount, but also the form of the recommended dietary carbohydrate must be considered, as both the quantity and quality of a carbohydrate can influence postprandial glycaemia (BrandMiller et al., 2002).
Dietary carbohydrates are digested and absorbed at different rates and to different extents in the gastrointestinal tract, depending on their botanical source and the physical form of the food (Cummings et al., 1997). Diets that contain large amounts of easily digested carbohydrate, which rapidly increase blood glucose and stimulate a large insulin response, may be detrimental to health (Englyst et al., 1999). Several studies have found an association between this type of diet and obesity and type 2 diabetes mel-litus (Salmeron et al., 1997a, b; Ludwig et al., 1999). Foods containing easily digested carbohydrates that produce a rapid rise in blood glucose are termed 'high glycaemic index (GI) foods'. The GI will be discussed in detail later in this chapter.
Low-GI foods are generally associated with greater satiety compared with high-GI foods (Haber et al., 1977; Holt et al., 1992; Holt & Miller, 1994; Liljeberg et al., 1999; Ludwig et al., 1999). The characteristic postprandial effects of high-GI foods - including rapid carbohydrate absorption, large fluctuations in blood glucose and insulin levels, together with reduced satiety - may contribute to overweight in the long run (Haber et al., 1977).
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