While nearly 10 percent of the U.S. population (25.8 million Americans) has diabetes, according to the American Diabetes Association (ADA), another 79 million people have prediabetes. Prediabetes, which is also known as impaired fasting glucose (IFG) or impaired glucose tolerance (IGT), is a condition in which a person’s blood glucose levels are elevated above what is considered healthy. As you probably guessed, this puts them at risk for developing diabetes, typically within 10 years, if they don’t take steps to head it off.
And diabetes is no small matter. In addition to altering your day-to-day life, it can put you at risk for heart disease, stroke, blindness, kidney disease, nervous system disorders and even amputation. What’s more, since there are often no symptoms of prediabetes, you could have it and not even know. The ADA recommends that you ask your doctor to conduct a prediabetes test if you are overweight and age 45 or older.
If you find that you are at risk, the good news is that research has shown that you can prevent or delay the development of type 2 diabetes through lifestyle changes. For example, in one new study, researchers examined the effects of a combination of whole grain and low insulin response grain products, fatty fish and bilberries on glucose metabolism and plasma lipidomic profile in people with prediabetes and features of metabolic syndrome. Additionally, they wanted to see whether an increase in long-chain polyunsaturated fatty acids (typically found in fish) is related to improved glucose metabolism.
The 12-week study included 106 men and women aged 40–70 years with prediabetes and at least two other features of metabolic syndrome. These included a BMI of 26–39 (i.e., overweight or obese), a waist circumference of 102 cm in men and 88 cm in women, high serum triglycerides levels, high blood pressure or use of medication for hypertension. (Eighty-six percent of the participants took at least one medication, but none of them used glucose lowering drugs.)
The subjects were divided into three groups:
1. Healthy Diet Group: These participants replaced their usual cereal products with breads that had a low glucose and insulin response (endosperm rye bread, sourdough whole meal wheat bread and commercial rye breads), contributing up to 25 percent of total energy intake. They also ate whole meal pasta. And they were allowed one portion of their usual cereal product (e.g. porridge, cereals or pastries) each day.
Whole grain has been associated with lower risk of obesity, insulin resistance, elevated fasting glucose and the incidence of diabetes. Rye bread has been shown to induce a lower insulin response than wheat, and enhances early insulin secretion in people with metabolic syndrome.
This group was also instructed to eat 100–150 grams of fatty fish three times a week. The recommended fish were salmon, rainbow trout, bream, Baltic herring, roach, vendace, white fish, char, trout, red-fish, mackerel and anchovy. And the subjects were advised to avoid saturated fats, such as butter and cream, when preparing the fish.
Studies have demonstrated associations between fatty acids found mainly in fish or fish oil supplements, such as plasma eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), and lower prevalence of insulin resistance and type 2 diabetes. However, clinical trials have produced conflicting results, and the exact mechanisms for the impact on glucose metabolism are poorly understood, which is why the authors were so interested in looking at the connection between fatty acids and improved glucose metabolism.
Finally, the subjects in this group were asked to eat three portions per day of bilberries, frozen, pureed and as dried powder, which was the total equivalent to 300 grams of fresh bilberries. A maximum of three to four portions a week of other berries was allowed.
Why bilberries? Bilberries, which are similar to blueberries and native to Northern Europe, are rich in antioxidants known as polyphenols, especially anthocyanins. Animal studies have suggested that polyphenols may help carbohydrate metabolism by decreasing glycemic responses after meals and fasting hyperglycemia, in addition to improving acute insulin secretion and insulin sensitivity. And human studies have shown berries or anthocyanin extracts can improve LDL cholesterol oxidation, lipid peroxidation, total plasma antioxidant capacity and dyslipidemia.
2. Whole Grain Enriched Diet (WGED) Group: The second group ate the same grain products as the first group. They were also given whole grain oat biscuits and were allowed to consume one portion per day if they wanted. They were not asked to change their fish or berry consumption.
3. Control Diet Group: This group replaced their habitually used breads with refined wheat breads and other cereal products (e.g., porridge or pasta) with low-fiber products. A maximum of two portions of rye products per day was allowed, while bilberries were not allowed and other berries were allowed a maximum of four times per week. Finally, this group was instructed to eat fish no more than once a week.
At baseline and at the end of the 12 weeks, a two-hour oral-glucose-tolerance test (OGTT) was conducted to calculate the rise in glucose and insulin. Additionally, the disposition index (DI) and insulinogenic index (IGI) were used as measures of insulin sensitivity and insulin secretion.
Before we get into what researchers discovered, let’s back up and break down some of the medical jargon.
Insulin sensitivity is how responsive your tissues are to insulin in permitting glucose clearance. When a healthy person consumes a meal that is high in sugar, insulin should spike, pushing glucose into their tissues rapidly, and then dissipate. For a person who has poor insulin sensitivity, though, the insulin and glucose levels remain elevated due to an inability to force glucose into muscle tissues, forcing the pancreas to produce more insulin. Abnormally low insulin sensitivity is called insulin resistance and will eventually require medical intervention.
OK, now that we have that covered, back to the results we go. There were no statistically significant differences between the groups at baseline, but the measurements after 12 weeks showed promise.
The Healthy Diet appeared to improve glucose metabolism and altered plasma lipidomic profile significantly, which researchers said suggests that the intake of whole grain and low insulin response grain products, fatty fish and bilberries had a positive effect on insulin secretion and glucose disposal. However, this diet did not alter insulin resistance.
As for the WGED Group, subjects saw only minor changes. While there was a trend toward improved levels in the two-hour glucose test, the same could not be said for the IGI and DI (insulin sensitivity) measurements.
Breaking Down the Results
Now, the point of this study was to look at the effect of the combination of the grain products, fish and bilberries, but researchers viewed the results through the lens of past research in an attempt to better understand what specifically may have caused the beneficial effects, and also to determine why insulin resistance was not improved.
First, for all of the groups, there was an association between the increases in plasma fatty acids EPA and DHA content and improved glucose metabolism. Besides the fatty fish, researchers hypothesized that bilberries may also have played a role in the improved glucose metabolism. Unfortunately, though, they did not have a biomarker that allowed them to make a good estimation of its specific effects. But they did cite another recent study that showed that insulin sensitivity was enhanced after a six-week dietary supplementation with bioactive substances from bilberries in 32 obese, insulin-resistant persons.
Regarding the question of insulin resistance, past research has mostly involved fish oil supplements and the studies have varied in terms of methods used to assess glucose metabolism, health status of participants, diet and duration of the study. Improvements in insulin resistance have thus far not been observed in healthy individuals or diabetic persons, but have been seen in obese individuals, which led the authors to say that their prediabetic study population may have been the ideal target group.
However, since the Healthy Diet did not alter insulin resistance, and improved insulin secretion and glucose disposal existed only in those subjects who had the highest changes in EPA and DHA, they said, “Future studies are needed to confirm these results and to find the optimal amount of fish needed to achieve improvement in insulin metabolism in subjects with IFG or IGT [prediabetes].”
As for the carbohydrate modification, other research has also concluded that a high-carbohydrate, low-glycemic-index diet has been shown to improve insulin sensitivity measures in people with impaired glucose tolerance or type 2 diabetes.
When all was said and done, researchers concluded: “Our results suggest that diet rich in whole grain and low insulin response grain products, bilberries, and fatty fish alter plasma lipidomic profiles and may be associated with improved glucose metabolism. Therefore, in long-term these dietary components may have a beneficial role in the prevention of type 2 diabetes in persons with impaired glucose metabolism.”
So if you’ve been diagnosed with prediabetes or worry that you may be at risk, you should consider switching out your usual grains for those mentioned here. Additionally, try to incorporate more fatty fish into your diet and/or add a fish oil supplement to your daily routine.
As for bilberries, you could check your local supermarket to see if it carries them, but they are rather acidic when eaten raw. However, you should be able to find them in supplement form at most health food stores.
 Lankinen, M, et al. Whole Grain Products, Fish and Bilberries Alter Glucose and Lipid Metabolism in a Randomized, Controlled Trial: The Sysdimet Study. PLoS One. 2011;6(8):e22646. 2011 Aug 25. [Epub ahead of print.]
 http://www.ehow.com/facts_5724311_insulin-vs_-insulin-sensitivity-definition.html. 30 Sept 2011.
 Stull AJ, et al. Bioactives in blueberries improve insulin sensitivity in obese, insulin-resistant men and women. J Nutr. 2010;140:1,764–1,768.