Dr. Costabile: All wholegrain foods (whole-meal pasta, barley soup, oat biscuits and breakfast cereals) used in our study were commercially available, except for the whole-wheat bread which was specially formulated for the study. In fact, the bread consumed by the participants was a sourdough bread (90% whole-wheat flour and 10% endosperm rye flour), developed within the HealthGrain project.

WGC: By the end of the study, participants were eating about 136g of whole grain per day. This is much higher than recommendations in most countries, including in the US, where it’s recommended we all eat 48g or more per day. Have any other studies you’re aware of used similar quantities?

Dr. C: The amount of test foods is usually maximized in experimental conditions to be able to appreciate their health effects without increasing too much the number of people enrolled in the study. However, the amount of wholegrain utilized in our study is rather similar to that employed in other trials. In fact, in the study by Ross et al. (Br. J. Nutr. 2011; 105:1492-502), a cross-over study with a 2-week intervention diet based on either whole grain or refined grain foods,  the amount of whole grain ingredients was 150 g/day as dry weight. Similarly, in the study by Kristensen et al. (J.Nutr. 2012; 142:710-6), an open label parallel intervention of 12 week duration, in which the participants were randomly allocated to an intake of refined cereals or whole grain products, the amount of whole grain ingredients was 105 g/day.

WGC: Interesting. So let’s cut right to the results. You and your team suggest that a “whole-grain diet was able to improve insulin action” in people with metabolic syndrome. What does this mean for diabetes treatment and prevention outside of the lab?

Dr. C: A reduction of postprandial [post-meal] insulin levels after consuming a whole grain rich diet may help preserve the functionality of pancreatic beta cells; in fact, a lower insulin demand to control postprandial blood glucose implies that pancreatic beta-cells are less stressed and this, in the medium/long term, could delay the onset of diabetes.

WGC: Sounds like a pretty good reason to switch to whole grains! Most research relating to diet and insulin is done with people who have been fasting.  It seems that your research is one of the few studies investigating diet and insulin metabolism in people after they eat (postprandial).  Why did you decide to do this? 

Dr. C: Fasting … is a more stable condition and, therefore, it is usually preferred to measure metabolic parameters.  However, people spend most of their time in the postprandial state.

WGC: So in a day and age when people snack much of the day, postprandial measurement gives you more real-life results?

Dr. C: We know that metabolic abnormalities may be present in the postprandial period even with perfectly normal fasting parameters and these abnormalities are relevant risk markers for diseases. As a matter of fact, abnormalities of lipid metabolism in the postprandial period predict an increased risk for cardiovascular diseases. Moreover, impaired postprandial glucose metabolism is a risk factor for the development of type 2 diabetes. In our study the whole grain rich diet had no effect on the metabolic parameters evaluated in the fasting state but, nevertheless, it was very effective in improving postprandial metabolism.

WGC:  So your study showed that choosing whole grains was beneficial to blood sugar and insulin management. Fascinating.  Before we finish, do you have any simple messages you’d like to deliver to consumers about whole grains, based on this study or any other research you have done?

Dr. C: Dietary fiber was for long considered the only important component of whole grains with health protective features. Now, more and more evidence shows that whole grains also contain other protective compounds, such as oligosaccharides and phytochemicals, (also referred to as bioactive substances) including antioxidants, minerals, vitamins, lignans and phenolic compounds, which have been linked to a reduced risk of cardiovascular disease, cancer, diabetes, obesity and other chronic diseases.

Therefore, whole grain foods are “packages” of nutrients, other health-protective components and fiber. Together these substances probably work far better than one of them alone. In fact, it is becoming more and more evident that the synergistic action of the several bioactive compounds (not just any single one of them) contributes to maintain the body functions in their physiological equilibrium.

The evidence available in the literature supports the use of whole grain foods because, among other health benefits, it is associated with:

• a lower risk of type 2 diabetes, obesity and coronary heart disease
• improved glucose, insulin and lipid metabolism  (particularly in the postprandial period)
• lower risk of constipation and other intestinal problems.

WGC: Thank you so much, Dr. Costabile. This blog went into a bit more scientific depth than we usually do, but we appreciate the opportunity to share your thoughts directly with our readers. (Kelly)