It’s common wisdom that people with diabetes — just like people without it — should eat a variety of fruits and vegetables to optimize nutrition and health. In addition to their many beneficial micronutrients (including vitamins and minerals), many fruits and vegetables contain a significant amount of fiber, and some have a low glycemic index — meaning that they’re less likely to spike your blood glucose than other foods.
But many people struggle to eat enough fruits and vegetables, especially fresh ones that usually need to be consumed shortly after they’re bought. So a recent study on blueberry consumption in men with type 2 diabetes was notable for a couple of different reasons. First, it tested the effect of just one simple dietary intervention. And second, it used a powder made from freeze-dried blueberries, which many people might find easier to store and use than fresh blueberries — especially since a small amount of this powder is equivalent to a much larger volume of fresh blueberries.
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Improvements seen in HbA1c and triglycerides
Published in the journal Current Developments in Nutrition, the study involved 52 overweight men with type 2 diabetes, ages 51 to 75. All of them were U.S. military veterans, and all took non-insulin medications for their diabetes (none took insulin). Participants were randomly assigned to one of two study groups. The first group took 22 grams of freeze-dried blueberries with meals each day for 8 weeks, while a second control group took the same amount of a different powder containing the same amount of energy and carbohydrate as the blueberry powder.
After 8 weeks, the blueberry group showed several improvements over the control group. As noted in a press release from the U.S. Highbush Blueberry Council, which funded the study, this group had better HbA1c (a measure of long-term blood glucose control) — an average of 7.1% versus 7.5% — along with lower fructosamine levels, which indicate medium-term blood glucose control. Members of the blueberry group also had lower blood triglyceride levels, an average of 180 versus 200 mg/dl.
Several other measurements weren’t significantly different between the two groups, including fasting blood glucose, serum insulin, total cholesterol, HDL and LDL cholesterol, C-reactive protein (a measure of inflammation), blood pressure and body weight.
Benefits could be from phytochemicals or fiber
As noted in the study, there are a number of different reasons why blueberries might have had the beneficial effects that were seen. Blueberries are a good source of a group of chemicals (sometimes called phytochemicals, or biologically active compounds) called polyphenols. One variety of polyphenols in particular, called anthocyanins, is responsible for giving blueberries their color and has been associated with reducing the risk of type 2 diabetes in previous studies. The blueberry powder was much higher in anthocyanins (261.8 versus 2.2 grams) and total measured polyphenols (765.6 versus 48.8 grams) than the control powder.
There were other notable differences between the two powders used in the study. While they were almost perfectly matched in energy (85 versus 84 calories) and carbohydrate (20.2 versus 20.9 grams) content, the blueberry powder was significantly higher in fiber (5.2 versus 0.3 grams) and potassium (104.7 versus 3.2 grams).
While the benefits seen in this study from consuming freeze-dried blueberries are encouraging, the researchers also noted several limitations to the study. One is that the number of participants was small, which may have made it more difficult to account for differences between the two groups — even though the two groups were randomly decided. If enough people in the blueberry group happened to have different lifestyle habits or even genetic factors, this could have influenced the study’s results.
The fact that the study didn’t control for fiber content — by using a control powder with the same amount of fiber as the blueberry powder — also calls into question whether a cheaper fiber supplement might have led to the same improvements seen from taking blueberries. This is an especially important consideration because a study intake survey showed that participants consumed, on average, only about 15 grams of fiber per day. For those who were assigned to the blueberry group, that means daily fiber intake increased by an average of about 35%, versus only about 2% in the control group.
Still, the study points to possible benefits and few risks from taking freeze-dried blueberries as a dietary supplement. “While the results cannot be generalized to all populations, they add to the evidence that a dietary intervention with a realistic serving of blueberries may be an effective strategy to improve metabolic factors associated with type 2 diabetes,” says Kim Stote, PhD, MPH, RDN, the study’s lead investigator and a researcher at the Albany Stratton VA Medical Center in New York, in the press release.
Looking to learn about more foods that may help with diabetes? Read “Bitter Melon, Diabetes,” “Leaves and Fruits for Diabetes,” “Turmeric and Diabetes: 10 Ways Turmeric Can Help” and “Cinnamon and Diabetes: An Update.”