Glycemic index of whole grains
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Glycemic Index of Whole Grains: Key Findings
Whole Grains vs. Refined Grains: Glycemic Response
Whole grain foods generally have a lower glycemic index (GI) compared to refined grains, leading to reduced postprandial (after-meal) blood glucose and insulin levels. This effect is consistently observed in systematic reviews and meta-analyses, which show that whole grain intake significantly lowers postprandial glycemia and insulinemia, and may also improve long-term glycemic control as measured by HbA1c, a marker of average blood sugar over time 45. These benefits are linked to a reduced risk of developing type 2 diabetes .
Variability in Glycemic Index Among Whole Grain Foods
Not all whole grain foods have the same GI. The GI of whole grain products can range from low to high, depending on the type of grain, its processing, and its physical structure. For example, whole grain pilaf (made from intact whole grains) has a medium GI (about 59), while instant brown rice and whole maize ugali (made from milled whole grains) have high GI values (above 70). The integrity of the grain structure plays a crucial role: foods with more intact bran and germ tend to have a lower GI, while those that are milled or processed more finely have a higher GI 168.
Impact of Processing on Glycemic Index
The degree of processing significantly affects the GI of whole grain foods. Less-processed whole grains, such as those that are minimally milled or left intact, result in lower postprandial blood glucose spikes compared to finely milled whole grain products. This is true even when the nutrient content is similar, highlighting the importance of grain structure in glycemic response 168. For example, less-processed whole grain foods led to 6–9% lower postprandial glucose responses compared to finely milled versions in people with type 2 diabetes .
Role of Dietary Fiber and Starch Composition
The type and amount of dietary fiber in whole grains also influence their GI. Whole grain rice lines with higher soluble dietary fiber (SDF) content have lower GI values, suggesting that SDF plays a positive role in reducing the glycemic impact of whole grains. Starch composition, particularly the ratio of resistant starch and slowly digestible starch, also contributes to lower GI values in some whole grain products 39.
Multigrain and Extruded Whole Grain Products
Multigrain whole grain products, especially those combining different grains and legumes, tend to have moderate GI values (around 63–66), which are lower than those of refined wheat products. These products are also stable and acceptable in taste, making them suitable for regular consumption to help prevent metabolic syndrome . Extrusion processing can alter the GI of whole grains, but some extruded whole grains, such as oats and sorghum, maintain lower GI values due to higher resistant starch and dietary fiber content .
Whole Grains, Glycemic Load, and Inflammation
Diets high in whole grains and low in glycemic load are associated with reduced systemic inflammation in people with diabetes. This effect is independent of body weight and glycemic control, and may help prevent cardiovascular complications by reducing oxidative stress and improving insulin sensitivity .
Conclusion
Whole grains generally have a lower glycemic index than refined grains, but the actual GI can vary widely depending on the type of grain, its processing, and its fiber and starch composition. Intact and minimally processed whole grains are most effective at lowering postprandial blood glucose. Including a variety of whole grains, especially those with higher soluble fiber and less processing, can help manage blood sugar and reduce the risk of type 2 diabetes and related complications 12345689+1 MORE.
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