Glycemic benefit more robust with less-processed whole-grain breads
Adults with type 2 diabetes may derive superior glycemic benefits from breads made with less-processed vs. more-processed whole grains, according to findings published in Diabetes Care.
“The results from this short-term study indicate that not all wholegrain foods are created equal, with less-processed whole grains potentially better for us. We looked at blood glucose control, which is important for people with diabetes,” Andrew N. Reynolds, PhD, a postdoctoral research fellow in the department of medicine and the department of human nutrition at the University of Otago in Dunedin, New Zealand, told Endocrine Today. “When considering the three breads made with roller-milled whole-grain flour, there was an inverse association indicating the larger the whole-grain particle size, the smaller the postprandial response.”
Reynolds and colleagues measured blood glucose levels for 15 adults with type 2 diabetes (mean age, 64 years; 44% women) who ate one of four types of bread. The four bread types were composed of 100% stoneground whole-grain flour; 100% roller-milled whole grain; 50% roller-milled whole-grain flour and 50% kibbled whole grain; or a combination of roller-milled whole-grain flour (40%), intact whole grain (30%) and kibbled whole grain (30%).
A single test required participants to eat four slices of one type of bread, after which the researchers measured blood glucose at 15-minute intervals for 1 hour and then 30-minute intervals for the next 2 hours. The participants completed the test with each bread type on different days based on random assignment. The researchers assessed glycemia using incremental area under the blood glucose curve (iAUC), glucose levels during the 3 hours after the meal and at 3 hours.
Effect on glycemic measures
According to the researchers, among roller-milled flour-based breads but not the stone-milled types, iAUC followed “an inverse linear trend” with increasing grain size. The researchers also noted that breads that were composed of bigger grains had smaller values for iAUC (P .003), postprandial glucose (P .006) and 3-hour glucose (P .001).
More specifically, iAUC was 375 mmol/L–1 min–1 for bread made with the mix of roller-milled whole-grain four, intact whole grain and kibbled whole grain; 503 mmol/L–1 min–1 for stone-milled whole-grain flour bread; 595 mmol/L–1 min–1 for the 50% roller-milled whole-grain flour and 50% kibbled whole-grain bread; and 641 mmol/L–1 min–1 for the 100% roller-milled whole-grain bread.
The 3-hour mean blood glucose level was 9.3 mmol/L for bread made with the mix of roller-milled whole-grain four, intact whole grain and kibbled whole grain; 10.62 mmol/L for stone-milled whole-grain flour bread; 10.39 mmol/L for the 50% roller-milled whole-grain flour and 50% kibbled whole-grain bread; and 10.17 mmol/L for the 100% roller-milled whole-grain bread.
The mean blood glucose level after 3 hours was 8.24 mmol/L for bread made with the mix of roller-milled whole-grain four, intact whole grain and kibbled whole grain; 10.45 mmol/L for stone-milled whole-grain flour bread; 10.17 mmol/L for the 50% roller-milled whole-grain flour and 50% kibbled whole-grain bread; and 10.35 mmol/L for the 100% roller-milled whole-grain bread.
Redefining whole grain
“Our results are potentially of clinical relevance to people with diagnosed diabetes and to dietary recommendations aimed at those with prediabetes and populations with a high proportion of obese individuals at risk for diabetes,” the researchers wrote.
In addition to what this means for the diet of those with diabetes, the researchers also suggested that this study could be the basis for a reexamination of food labeling.
“We are looking at ways to help people improve their blood glucose control. Studies like these can be of interest to food industry, who can alter wholegrain products found in the supermarket to include more intact, less-processed whole grains,” Reynolds said. “Studies like these may also tweak dietary recommendations, guiding people towards making small changes that protect their health.” – by Phil Neuffer
Disclosures: The study was funded by a grant from the Baking Industry Research Trust of New Zealand and the Riddet Centre of Research Excellence. One author reports he was supported by the Healthier Lives National Science Challenge. The funders report they did not play a role in the study design, conducting the study, the data analyses or the interpretation of results.