A large analysis of randomized trials has examined whether eating more whole grains can improve the risk factors linked with heart disease and type 2 diabetes. Across 87 trials involving 6,529 adults, whole-grain diets were associated with modest improvements in cholesterol, blood pressure, fasting glucose, body weight and several other cardiometabolic markers.
The findings support replacing some refined grains with minimally processed whole-grain foods. They do not show that whole grains cure diabetes, cause major weight loss or prevent heart attacks on their own. Most of the trials were short, and they measured risk factors rather than cardiovascular events.
Here is what the study found, how large the changes were and how people can interpret the results without turning a useful food choice into an unrealistic promise.
Key takeaways
- The review included 87 randomized trials reported in 101 publications, with 6,529 adult participants.
- Compared with lower-whole-grain, refined-grain or usual diets, whole-grain interventions produced modest improvements in several cardiovascular and metabolic risk factors.
- The clearest clinically meaningful change in the main analysis was a reduction in LDL cholesterol.
- Average changes in body weight, fasting glucose and HbA1c were small and were not considered clinically important by the researchers.
- Dose-response analyses suggested that many benefits were greatest around 60 to 100 grams per day of whole grains measured as dry weight, roughly described by the researchers as four to six servings.
- The median trial duration was only eight weeks, and the studies did not establish that whole grains prevent heart attacks, strokes or diabetes complications.
- For people with diabetes, replacing refined grains can be useful, but whole-grain foods still contain carbohydrate and may affect glucose levels.
What counts as a whole grain?
A grain is considered whole when it retains the bran, germ and endosperm in the same proportions as the original kernel. Refining usually removes the bran and germ, along with some fibre and nutrients.
Examples of whole-grain foods include:
- oats and oatmeal
- barley
- brown or wild rice
- bulgur wheat
- rye
- wholewheat bread, couscous and pasta
- foods made from whole maize or corn
A product can contain some whole grain without being an especially healthy choice. Sugary breakfast cereals, biscuits and highly processed snack bars may carry a whole-grain claim while also containing substantial added sugar, salt or saturated fat. The overall product still matters.
How the researchers studied whole grains
The researchers performed a systematic review and dose-response meta-analysis published in the European Heart Journal. They searched major research databases for randomized trials in adults that compared diets higher in whole grains with diets lower in whole grains, refined-grain diets, usual care or other dietary advice.
Eligible trials lasted at least two weeks. The review assessed body weight, waist circumference, blood lipids, blood pressure, fasting glucose, HbA1c, insulin resistance, inflammatory markers, quality of life and adverse events.
Combining many trials can provide a more precise estimate than relying on one small study. However, a meta-analysis also inherits the differences and weaknesses of the studies it combines. The trials varied in the types and amounts of grain used, the comparison diets, participant characteristics and duration.
What did the analysis find?
In the main comparison between whole-grain interventions and control diets, the average changes included:
- LDL cholesterol: 0.13 mmol/L lower. The researchers judged this change clinically important, with moderate-certainty evidence.
- Total cholesterol: 0.17 mmol/L lower, with high-certainty evidence.
- Body weight: 0.51 kg lower, with high-certainty evidence. The researchers considered the average change too small to be clinically important on its own.
- Waist circumference: 0.60 cm lower, also considered a small change.
- Systolic blood pressure: 1.50 mmHg lower, with moderate-certainty evidence.
- Fasting plasma glucose: 0.07 mmol/L lower, with moderate-certainty evidence. This was a very small average difference.
- HbA1c: 0.05 percentage points lower, with moderate-certainty evidence. This was also considered clinically small.
The analysis also found small reductions in triglycerides and the inflammatory marker interleukin-6. Results for some other outcomes were less certain or were sensitive to individual studies.
This pattern is important. The study did not find one dramatic effect. It found several generally modest changes, with the strongest practical signal involving blood lipids rather than glucose or weight.
How much whole grain appeared most useful?
The researchers also examined dose-response relationships. Many of the largest estimated improvements occurred around 60 to 100 grams per day of whole grains measured as dry weight. They described this as approximately 115 to 190 grams of prepared food, or around four to six servings per day.
That figure should not be treated as a universal prescription. Serving sizes differ between products, countries and studies. The trials also tested different grains and comparison diets. Eating a bowl of oats is not directly equivalent to eating the same weight of bread, rice or another grain.
The most useful interpretation is usually to focus on substitution: replace some refined-grain foods with minimally processed whole-grain choices that fit a person’s culture, budget, nutritional needs and glucose-management plan.
What does this mean for people with diabetes?
Whole grains provide fibre and often produce a different glucose response from more refined versions of the same food. They can form part of a balanced eating pattern for many people with type 1 diabetes, type 2 diabetes or prediabetes.
However, whole-grain foods are not carbohydrate-free. Bread, rice, pasta, oats and cereals can all raise blood glucose. The size of the rise depends on the portion, the specific food, how it is processed, what it is eaten with, activity and individual physiology.
The meta-analysis found only a very small average improvement in fasting glucose and HbA1c. It should not be used as a reason to stop medication, change insulin doses independently or expect whole grains to reverse diabetes.
People who monitor glucose can look at their own patterns after meals. A registered dietitian or diabetes team can help adapt whole-grain portions to medication, insulin, activity and personal targets.
Practical ways to make a whole-grain swap
- Choose porridge oats or a lower-sugar whole-grain cereal instead of a refined breakfast cereal.
- Try wholewheat or seeded bread in place of white bread.
- Replace some white rice with brown rice, barley or bulgur.
- Use wholewheat pasta, adjusting the portion to match your glucose-management plan.
- Add oats or barley to soups and stews.
- Pair grain foods with vegetables, pulses, protein and healthy fats rather than eating a large portion on its own.
- Increase fibre gradually and drink enough fluid unless a healthcare professional has advised fluid restriction.
When comparing packaged foods, check the ingredients list rather than relying only on the colour of the bread or front-of-pack claims. Look for a whole grain, such as wholewheat flour or whole oats, near the beginning of the list. Also compare fibre, added sugar, salt and saturated fat.
Who may need individual advice?
Higher-fibre foods are suitable for many people, but individual needs differ. Speak with a qualified healthcare professional or dietitian if you have:
- coeliac disease or another condition requiring strict gluten avoidance
- gastroparesis or significant digestive symptoms
- advanced kidney disease with a personalised potassium, phosphate or fluid plan
- a history of bowel narrowing or recent gastrointestinal surgery
- insulin or medicines that can cause low glucose when food intake changes
Seek personalised guidance rather than abruptly increasing fibre or changing carbohydrate intake.
Important limitations
The study has several limitations that keep the results in perspective:
- The median follow-up was about eight weeks, so long-term adherence and effects remain uncertain.
- The trials measured risk factors, not heart attacks, strokes, diabetes complications or deaths.
- Whole-grain types, doses and comparison diets differed substantially between studies.
- Participants generally could not be blinded to the food they were eating.
- Some outcomes showed substantial variation between studies.
- Adverse events were inconsistently reported and were supported by low-certainty evidence.
- Evidence at very high whole-grain intakes was sparse.
The results therefore support whole grains as one part of a healthy eating pattern, not as a stand-alone treatment.
The bottom line
This meta-analysis of 87 randomized trials found that diets higher in whole grains produced modest improvements across several cardiometabolic risk factors. The most meaningful average change was in LDL cholesterol. Changes in glucose, HbA1c and body weight were much smaller.
For most people, the practical message is simple: replacing some refined grains with minimally processed whole-grain foods is a reasonable step within an overall balanced diet. People with diabetes should still consider carbohydrate portions, monitor their own response and make medication decisions with their healthcare team.
Sources
- Naghshi S, et al. Whole-grain consumption and cardiometabolic risk: a meta-analysis of randomized trials. European Heart Journal. Published online 15 September 2026. doi:10.1093/eurheartj/ehag519.
- European Society of Cardiology. Four to six servings of wholegrain per day lowers risk factors for heart disease. 16 September 2026.
- NHS. The Eatwell Guide.
This article provides general education and is not individual medical advice. Speak with a qualified healthcare professional before making significant dietary or medication changes, particularly if you use insulin or medicines that can cause low glucose.