Carbohydrate-rich diets lead to continuous pancreatic stimulation and repeated postprandial insulin secretion. This type of diet has been hypothesized to lead to insulin resistance, ß cell dysfunction, and, ultimately, type 2 diabetes (Zammit et al, 2001). Many studies have shown that diets with lower glycemic indices and higher fiber content decrease the development risk of type 2 diabetes and heart diseases, contribute to a higher quality of life for diabetics, and have some preventive and restorative effects against insulin resistance and metabolic syndrome (Amano et al, 2004; Leeds, 2002; Liu et al, 2000). Furthermore, several studies have investigated the short-term effects of different types of breads on glucose metabolism. In a study in which 2-h postprandial effects of white bread, wheat bran bread, and whole grain bread were compared (Mesci et al, 2008), no difference was found among the three types of breads with respect to glycemic effects (Figures 39.1 and 39.2). Hlebowicz et al. (2009) found no difference in postprandial blood glucose response or gastric emptying after the ingestion of rye wholemeal bread compared to white wheat bread. Different types of breads do not cause significant differences in the postprandial glycemic response. This also applies for breads that contain different levels of fiber content (Heinonen et al, 1985; Jenkins et al, 1983; Juntunen et al, 2003; Liljeberg et al, 1992). However, different breads show a difference with respect to postprandial insulin response (Juntunen et al, 2002). In particular, rye bread leads to a lower postprandial insulin response compared to other types of breads (Table 39.2).
Rosen et al. (2009) found that whole grain rye breads and endosperm rye products induced significantly (p < 0.05) lower insulinemic indices compared to white wheat bread. Endosperm and whole grain rye products induced low acute insulinemic responses and improved glycemic profiles. The results also suggested that the rye products possess beneficial appetite-regulating
Whole grain bread H Rye bread I Wheat bran bread □ White bread
Glycemic effects of different kinds of bread. Three different bread types consumed as alternatives to white bread showed similar increases in blood glucose levels as white bread in diabetic patients. Results are expressed as mean ± SD; n = 121. Source: Reproduced from Mesci, B, Oguz, A, Sagun, H. G, Uzunlulu, M, Keskin, E. B, and Coksert, D. (2008). Dietary breads: Myth or reality? Diabetes Res. Clin. Pract. 81, 68—71.
properties. Preservation of the intact botanical structure of cereal grains has also been shown to lower the insulin response (Heaton et al, 1988). These effects may be mediated through glucose-dependent insulinotropic polypeptide and glucagon-like peptide 1 (GLP-1; Juntunen et al, 2002), which are the most important insulinotropic incretins.
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