Wholegrain Particle Size Influences Postprandial Glycemia in Type 2 Diabetes: A Randomized Crossover Study Comparing Four Wholegrain Breads

Abstract

Wholegrain foods vary in the extent of processing. We investigated whether wholegrain particle size in bread influences postprandial glycemia in type 2 diabetes. RESEARCH DESIGN AND METHODS Postprandial glycemia (incremental area under the blood glucose curve [iAUC]) was measured after consumption of three breads made with roller-milled wholegrain flour and added grains and a fourth made with stone-ground flour. All flours and grains were 100% wholegrain wheat. Breads were nutrient matched. RESULTS Fifteen adults (64 6 10 years, HbA 1c 58 6 13 mmol/mol) completed the study. iAUC for the three breads made with roller-milled flour ranged from 376 to 641 mmol 21 min 21 , inverse linear trend for grain particle size P 5 0.039. The iAUC for stone-ground wholegrain bread (503) was smaller than predicted from mean particle size. CONCLUSIONS Wholegrain structural integrity in bread is a determinant of glycemic response. These findings have implications for dietary advice and the definition of the term "'wholegrain." Diets high in whole grains are associated with reduced incidence and mortality from several noncommunicable diseases (1) and are recommended in the management of type 2 diabetes (2). Although wholegrain bread has been a staple food in many cultures for thousands of years (3), wholegrain bread currently available in the food supply is frequently made from finely milled reconstituted components of whole grains (4). The structural integrity of food has been shown to influence cardiometabolic risk factors in people with type 2 diabetes (5). We have considered the extent to which the structural integrity of whole grains in bread, measured by particle size, influences postprandial glycemia in adults with type 2 diabetes. RESEARCH DESIGN AND METHODS This single-center, randomized, crossover study was prospectively registered (ACTRN12617000328370, anzctr.org.au

Whole-Grain Processing and Glycemic Control in Type 2 Diabetes: A Randomized Crossover Trial

“…Older acute studies considering the structural integrity of whole grains on postprandial glycemia also confirm our findings (29,31,32). More recently, we have shown an inverse trend between postprandial glycemia and whole-grain particle size in breads in a controlled setting (11). Current definitions of whole grains permit a wide range of processing methods and require that reconstitution of grain components is to the same ratio as they exist in an intact grain (7,8).…”

“…Older acute studies considering the structural integrity of whole grains on postprandial glycemia also confirm our findings ( 29 , 31 , 32 ). More recently, we have shown an inverse trend between postprandial glycemia and whole-grain particle size in breads in a controlled setting ( 11 ).…”

“…There is evidence that the acute glycemic response to whole-grain foods is greater when grains have been finely milled (10). More recently, we have shown that the glycemic response to four different whole-grain wheat breads is related to the degree of grain processing in adults with type 2 diabetes (11).…”

“…A body of work supports benefits in postprandial glycemia when comparing whole-grain consumption with refined grains ( 27 ). Fewer studies have considered glycemia following the consumption of intact or processed whole grains ( 11 , 28 – 30 ). To our knowledge, the longest intervention relevant to this issue by Järvi et al ( 28 ) reported on two different diets followed for 24 days by adults with type 2 diabetes.…”

Flour for Home Baking: A Cross-Sectional Analysis of Supermarket Products Emphasising the Whole Grain Opportunity

“…Bread-making mixes may be the only subcategory where smaller percentages of whole grain are declared, as these products tended to be refined with added seeds and grain to make a multi-grain product, which does not fit the definition of whole grain. Recent research regarding whole grain in food has been giving attention to milling methods, with micronized flour milling to assist with texture and sensory profiles to encourage consumption [27], while other research has focused more on glycaemic control and outcomes relevant in Type 2 Diabetes Mellitus [28,29], with concerns about the degree of milling. These issues may need to be resolved to help progress discussions regarding the definition of whole grain foods [30].…”