Research shows that eating less processed whole grains improves blood sugar control in people with type 2 diabetes compared to eating milled whole grains. A 12-week randomized trial of 160 adults found that those eating minimally processed whole grains had HbA1c levels that were 2.2 mmol/mol lower than those eating ground whole grain flour, despite eating similar total amounts of whole grains. According to Gram Research analysis, this suggests that grain processing itself influences how your body manages blood sugar.
A new study shows that people with type 2 diabetes get better blood sugar control when they eat whole grains that haven’t been heavily processed or ground into flour. Researchers gave 160 adults with type 2 diabetes either minimally processed whole grains (like intact grain kernels) or milled whole grains (ground into flour) for 12 weeks. The group eating less processed grains had better blood sugar levels, even though both groups ate similar amounts of whole grains overall. According to Gram Research analysis, this finding suggests that how much a grain is processed matters more than we thought for managing diabetes.
Key Statistics
A 12-week randomized controlled trial of 160 adults with type 2 diabetes found that eating less processed whole grains reduced HbA1c levels by 2.2 mmol/mol compared to eating milled whole grains, with 143 participants completing the study.
Research published in The American Journal of Clinical Nutrition in 2026 showed that less processed whole grain foods improved blood sugar control in adults with type 2 diabetes without any change in body weight between intervention groups.
A randomized trial of 160 people with type 2 diabetes found that replacing normal grain foods with less processed whole grains for 12 weeks improved bowel habits compared to milled whole grain products.
In a 2026 study of 160 adults with type 2 diabetes, less processed whole grains provided approximately 20% of daily calories and produced clinically meaningful improvements in glycemic control compared to milled whole grains.
The Quick Take
- What they studied: Whether the way whole grains are processed (ground up versus left mostly intact) affects blood sugar control in people with type 2 diabetes
- Who participated: 160 adults with type 2 diabetes, average age 58 years old, who were overweight or obese. By the end of the study, 143 people completed it.
- Key finding: People who ate less processed whole grains had better blood sugar control (measured by HbA1c levels) compared to those eating milled whole grains. The difference was small but meaningful: a 2.2 mmol/mol improvement.
- What it means for you: If you have type 2 diabetes, choosing whole grains that are less processed (like steel-cut oats or whole grain kernels instead of whole wheat flour) may help you manage your blood sugar better. However, talk to your doctor before making big changes to your diet.
The Research Details
This was a randomized controlled trial, which is one of the strongest types of research studies. Researchers divided 160 adults with type 2 diabetes into two groups. One group received minimally processed whole grain foods (grains that were mostly left intact), while the other group received milled whole grain foods (grains that had been ground into flour). Both groups received enough food delivered to their homes for 12 weeks to feed their families, with instructions to replace their normal grain foods with the study foods.
The researchers measured blood sugar control using a test called HbA1c, which shows average blood sugar levels over the previous three months. They also tracked body weight, diet quality, and bowel habits. The study used an intention-to-treat approach, meaning they analyzed results for everyone who started the study, even if some people didn’t complete it perfectly.
Both groups received similar amounts of whole grains (about 20% of their daily calories), so the only real difference was how processed the grains were. This design helps isolate whether processing matters, rather than just eating more or less whole grain.
This research design is important because it controls for many factors that could confuse the results. By giving people actual food instead of just asking them to change their diet, researchers could be sure people were actually eating what was supposed to be tested. By making both groups eat similar amounts of whole grains, they could prove that processing itself makes a difference, not just eating more whole grains in general.
This study has several strengths: it was randomized (reducing bias), it had a good completion rate (89% of participants finished), it was published in a respected journal (The American Journal of Clinical Nutrition), and it used a real-world approach by delivering actual food to people’s homes. The main limitation is that 12 weeks is relatively short, so we don’t know if benefits last longer. Also, the study was done in one country, so results might differ in other populations.
What the Results Show
The main finding was clear: people eating less processed whole grains had better blood sugar control than those eating milled whole grains. Specifically, HbA1c levels dropped by an average of 2.2 mmol/mol more in the less processed group. While this might sound small, it’s clinically meaningful for diabetes management.
Interestingly, this improvement happened without any difference in body weight between the groups. Both groups maintained similar weight throughout the study. This suggests that the type of grain processing affects blood sugar control through mechanisms beyond just weight loss.
The researchers also found that total whole grain intake, refined grain intake, and overall nutrient intake were similar between groups. This is important because it proves the only real difference was how processed the grains were. The study foods made up about 20% of participants’ total daily calories in both groups.
Beyond blood sugar control, the study looked at other health measures. The only secondary finding that showed improvement was self-reported bowel habits, which improved more in the less processed whole grain group. This makes sense because less processed grains contain more fiber in its natural form. The researchers did not find significant differences in other measures between groups.
Previous small studies suggested that grain processing might matter for blood sugar, but this is one of the first larger, well-designed studies to confirm it. Most dietary guidelines recommend eating whole grains but don’t distinguish between different types of whole grain processing. This research supports the idea that guidelines should be more specific about choosing less processed whole grains when possible. The findings also suggest that simply replacing refined grains with milled whole grain flour (like whole wheat bread) might not be as beneficial as eating intact whole grains.
The study lasted only 12 weeks, so we don’t know if benefits continue longer or if people can stick with less processed grains over years. The study was done in one country, so results might differ for people from different backgrounds or with different food availability. The study didn’t look at specific types of less processed grains separately, so we don’t know if some work better than others. Finally, the study relied on people self-reporting some information like bowel habits, which can be less accurate than objective measurements.
The Bottom Line
If you have type 2 diabetes, consider choosing less processed whole grains (like steel-cut oats, whole grain kernels, or intact grain products) over milled whole grain products (like whole wheat flour or whole wheat bread). This change appears to help blood sugar control. However, this is based on one 12-week study, so talk with your doctor or a dietitian before making major diet changes. The evidence is moderately strong but not yet definitive.
People with type 2 diabetes should pay attention to this research. It may also be relevant for people trying to prevent type 2 diabetes or manage prediabetes, though this study didn’t test those groups. People without diabetes may not see the same benefits. Anyone with digestive issues might also benefit from the improved bowel habits noted in the study.
The study showed improvements in blood sugar control within 12 weeks. However, most people won’t see dramatic changes overnight. It typically takes 2 to 3 months of consistent eating habits to see meaningful improvements in HbA1c levels. Some people might notice improved digestion sooner, within days or weeks.
Frequently Asked Questions
What’s the difference between less processed and milled whole grains?
Less processed whole grains are mostly intact kernels, like steel-cut oats or whole grain berries. Milled whole grains have been ground into flour, like whole wheat flour or whole grain bread. The study found that intact grains work better for blood sugar control.
Can less processed whole grains help me lose weight if I have type 2 diabetes?
This study didn’t show weight loss benefits from less processed grains, but both groups maintained stable weight. However, the improved digestion noted in the study might help some people feel fuller longer, which could support weight management efforts.
How long does it take to see blood sugar improvements from eating less processed grains?
The study measured improvements after 12 weeks. Most people need 2 to 3 months of consistent eating changes to see meaningful improvements in HbA1c levels, though some people might notice better digestion within days or weeks.
Are less processed whole grains better for everyone or just people with diabetes?
This study only tested people with type 2 diabetes, so we don’t know if benefits apply to everyone. People without diabetes might see different results. Talk to your doctor about whether this approach is right for your specific health situation.
Should I stop eating whole wheat bread if I have type 2 diabetes?
This study suggests less processed grains may work better than milled whole grains like bread, but whole wheat bread is still better than refined white bread. Consider adding less processed options like steel-cut oats or whole grain kernels to your diet alongside whole grain bread.
Want to Apply This Research?
- Track the type of grain products you eat daily, noting whether each is less processed (intact kernels, steel-cut oats, whole grain berries) or more processed (whole wheat flour, whole grain bread, milled products). Rate each meal’s processing level on a scale of 1 to 5, with 1 being most processed and 5 being least processed.
- Replace one grain-based meal per day with a less processed whole grain option. For example, swap whole wheat bread for steel-cut oats at breakfast, or replace regular brown rice with farro or barley at lunch. Track which swaps you make and how you feel after eating them.
- Over 12 weeks, monitor your energy levels, digestion, and any changes in how you feel after meals. If you have access to blood sugar testing, track readings before and after meals with less processed grains. Share results with your healthcare provider at your next appointment to discuss whether this approach is working for you.
This research provides evidence that less processed whole grains may help with blood sugar control in type 2 diabetes, but it should not replace medical advice from your doctor or diabetes care team. Before making significant changes to your diet or grain intake, especially if you take diabetes medications, consult with your healthcare provider or a registered dietitian. Individual results may vary, and this study was conducted over 12 weeks, so long-term effects are not yet known. This information is for educational purposes and should not be used for self-diagnosis or self-treatment of diabetes.
This research translation is published by Gram Research, the science division of Gram, an AI-powered nutrition tracking app.