Oats

Healthy carbohydrates like whole grains are part of the solution, not the problem, when it comes to diabetes. In this study, researchers analyzed 29 randomized controlled trials (the gold standard of nutrition research) to see how whole grains and ancient grains might impact health outcomes in people with diabetes. They found that brown rice significantly improved HbA1c (a measure of blood sugar control over time) and BMI (a measure of weight based on height), that oats significantly improved cholesterol, and that millet significantly improved body weight. However, given the different grains and research methods used, it was difficult for the researchers to draw broad conclusions across the whole group of grains, indicating that more research is needed to understand these effects. 
Nutr Metab Cardiovasc Dis. 2024 May;34(5):1110-1128. doi: 10.1016/j.numecd.2024.03.005. Epub 2024 Mar 7. (Magi CE et al.)

Dietary guidelines around the world recommend making more of our grains whole, and researchers wonder if people in different countries are meeting these goals. In a study of 9,128 people across eight Latin American countries, the average person was eating less than one full serving (only 14.7 grams) of whole grain foods per day. Women and older adults were more likely to eat more whole grains, while people with lower incomes were less likely to eat more whole grains. The most commonly eaten whole grains in the survey were oatmeal, masa harina, whole wheat bread, corn chips, and wheat crackers.
European Journal of Nutrition. 2021 Jul 7. doi: 10.1007/s00394-021-02635-8.

In a large study of nearly 200,000 US adults, those eating whole grains most frequently had a 29% lower risk of developing type 2 diabetes across the approximately 30-year study period than those rarely or never eating whole grains, even after adjusting for other lifestyle factors. When looking at specific whole grain foods, common foods like whole grain breakfast cereal, oatmeal, whole grain bread, and brown rice were all linked with a lower risk of type 2 diabetes. The exception was popcorn, which was linked with a higher risk of type 2 diabetes when eaten more than once per day, perhaps due to its association with butter sauces or sugary flavorings.
BMJ. 2020 Jul 8;370:m2206. doi: 10.1136/bmj.m2206. (Hu Y et al.)

To better understand whole grains’ relationship with heart health, New Zealand’s Heart Foundation analyzed 19 meta analyses encompassing thousands of participants, for their September 2018 report entitled “Whole Grains and the Heart.” The authors conclude that “observational research suggests three [servings] of whole grains per day are associated with heart health benefits, and there are likely to be additional benefits with higher intakes. Intervention studies on risk factors are less compelling but show most consistent evidence of benefits for a small reduction in total and LDL cholesterol, especially in relation to oats and barley, and possibly improved [glycemic] control.”
Heart Foundation. 2018 Sept. (Gorton D et al.)