Glycaemic potency reduction by coarse grain structure in breads is largely eliminated during normal ingestion.

The hypothesis that coarse grain particles in breads reduce glycaemic response only if the particles remain intact during ingestion was tested. Three breads were formulated: (1) White bread (WB - reference), (2) 75 % of kibbled purple wheat in 25 % white bread matrix (PB) and (3) a 1:1 mixture of 37·5 % kibbled soya beans and 37·5 % of kibble purple wheat in 25 % white bread matrix (SPB). Each bread was ingested in three forms: unchewed (U), as customarily consumed (C) and homogenised (H). Twelve participants ingested 40 g available carbohydrate portions of each bread in each form, with post-prandial blood glucose measured over 120 min. Glycaemic responses to WB were the same regardless of its form when ingested. Unchewed PB had significantly less glycaemic effect than WB, whereas the C and H forms were similar to WB. Based on a glycaemic index (GI) of 70 for WB, the GI values for the C, U and H breads, respectively, were WB: 70·0, 70 and 70, PB: 75, 42 and 61, SPB: 57, 48 and 55 (%) (Least significant difference = 17·43, P < 0·05, bold numbers significantly different from WB). The similar glycaemic response to the H and C forms of the breads, and their difference from the U form, showed that the glycaemia-moderating effect of grain structure on starch digestion was lost during customary ingestion of bread. We conclude that the kibbled-grain structure may not effectively retard starch digestion in breads as normally consumed because it is largely eliminated by ingestive processes including chewing.

Equicarbohydrate partial exchange of kiwifruit for wheaten cereal reduces postprandial glycaemia without decreasing satiety.

Kiwifruit is a carbohydrate food of low glycaemic potency which could potentially be exchanged for starch-based foods in management of postprandial glycaemia. The effect of equicarbohydrate partial exchange of kiwifruit varieties 'Hayward' green (GR) and 'Zesy002' (SunGold; SG) for a starchy wheat-based breakfast cereal (WB) on the characteristics of the postprandial glycaemic response and satiety was therefore determined. A total of twenty non-diabetic subjects (mean age 36 years; mean BMI 24·5 kg/m2) consumed four meals, each containing 40 g available carbohydrate, in random order, after an overnight fast. The meals were: (1) glucose; (2) 70·29 g breakfast cereal; (3) 200 g of GR plus breakfast cereal (30·93 g); and (4) 200 g of SG plus breakfast cereal (27·06 g). Throughout the 180 min postprandial period, capillary blood glucose concentrations were monitored, and satiety rated by a visual analogue scale. Partial kiwifruit substitution of WB significantly reduced postprandial glycaemic response amplitude (glucose, 3·91; WB, 3·66; WB + GR, 2·36; WB + SG, 2·31  mmol/l; least significant difference (LSD) 0·64; P < 0·001) and incremental area under the blood glucose response curve (0-120 min) (glucose, 228; WB, 180; WB + GR, 133; WB + SG, 134 mmol/l × min; LSD 22·7; P < 0·001). The area between baseline and response remained positive in kiwifruit-substituted meals but became negative after 120 min with glucose and WB, indicating that kiwifruit improved homeostatic control. Kiwifruit substitution of cereal did not significantly reduce satiety. We conclude that either 'Hayward' or 'Zesy002' kiwifruit may be used in equicarbohydrate partial substitution of starchy staple foods to reduce glycaemic response and improve glucose homeostasis without decreasing satiety.