Abstract
Wholegrain flour produced by roller-milling is predominantly comprised of fine particles, while stoneground flour tends to have a comparatively smaller proportion of fine particles. Differences in flour particle size distribution can affect postprandial glycaemia in people with type 2 diabetes and postprandial insulinaemia in people with and without type 2 diabetes. No prior studies have investigated the effect of wholegrain flour particle size distribution on glycaemic or insulinaemic response among people with impaired glucose tolerance or risk factors for type 2 diabetes. In a randomised crossover study, we tested the 180-min acute glycaemic and insulinaemic responses to three wholegrain breads differing in flour particle size and milling method: (1) fine roller-milled flour, (2) fine stoneground flour, and (3) coarse stoneground flour. Participants (n = 23) were males and females with risk factors for type 2 diabetes (age 55–75 y, BMI >28 kg/m2, completing less than 150 min moderate to vigorous intensity activity per week). Each test meal provided 50 g available carbohydrate, and test foods were matched for energy and macronutrients. There was no significant difference in blood glucose iAUC (incremental area under the curve) between the coarse stoneground flour bread and the fine stoneground flour bread (mean difference −20.8 (95% CI: −51.5, 10.0) mmol·min/L) and between the coarse stoneground flour bread and the fine roller-milled flour bread (mean difference −23.3 (95% CI: −57.6, 11.0) mmol·min/L). The mean difference in insulin iAUC for fine stoneground flour bread compared with the fine roller-milled flour bread was −6.9% (95% CI: −20.5%, 9.2%) and compared with the coarse stoneground flour bread was 9.9% (95% CI: −2.6%, 23.9%). There was no evidence of an effect of flour particle size on postprandial glycaemia and insulinaemia among older people with risk factors for type 2 diabetes, most of whom were normoglycaemic.
Highlights
IntroductionWholegrain consumption can improve acute postprandial glycaemia compared with refined grains [1] and is associated with reduced risk of developing type 2 diabetes [2,3]
Among people with known risk factors for type 2 diabetes, there were no significant differences in glycaemic or insulinaemic response to breads made with coarse stoneground flour, fine stoneground flour, and fine roller-milled flour, the glycaemic response to the bread made from coarse flour was marginally lower than the two breads made from fine flour
Given that people are frequently unaware of having prediabetes, we considered that the cost and time involved in screening for participants who met the diagnostic of prediabetes or impaired glucose tolerance would have been prohibitive
Summary
Wholegrain consumption can improve acute postprandial glycaemia compared with refined grains [1] and is associated with reduced risk of developing type 2 diabetes [2,3]. Bread made with stoneground or coarse wholegrain flour results in a lower acute postprandial glycaemic response among people with type 2 diabetes compared to bread made with roller-milled wholegrain flour [3,8], but the same effect has not been shown for people with normal glucose tolerance [6,9,11]. Consumption of foods made from coarse compared with finely milled flours can result in reduced postprandial insulinaemia in both people with diabetes and those with normal glucose tolerance [6,8,9]
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