Obese, non-diabetic, and insulin-resistant participants who consumed a blueberry smoothie daily for six weeks experienced a 22 percent change in insulin sensitivity, compared to only 4.9 percent in the placebo group, state findings published in the Journal of Nutrition.
“To our knowledge, this is the first reported human study that evaluated the effect of daily dietary supplementation with bioactives in blueberries on whole-body insulin sensitivity in obese, non-diabetic, and insulin-resistant men and women,” wrote the researchers, led by Professor William Cefalu at the Center for the Study of Botanicals and Metabolic Syndrome, Louisiana State University System.
“The uniqueness of this study relates to the design, which was randomized, double blinded, and placebo controlled. By design, the blueberry and placebo smoothies were identical in physical appearance and macronutrient content with the exception of adding the blueberry bioactives to the blueberry smoothie.
The major finding was that daily consumption of whole blueberry bioactives for 6 wk improved insulin sensitivity in a population at high risk for type-2 diabetes compared with ad libitum dietary intake alone,” they added.
Consumer interest in blueberries and the compounds they contain has increased in recent years, following results from studies reporting a wide range of health benefits, most notably for brain health and reducing the risk of Alzheimer’s.
The beneficial effects of the blueberries are thought to be linked to their flavonoid content - in particular anthocyanins and flavanols.
Despite numerous studies reporting the benefits of blueberries, no human study has looked at the effects of higher blueberry consumption on insulin sensitivity in people at high risk of developing type-2 diabetes.
Prof Cefalu and his co-workers recruited 32 obese, non-diabetic, and insulin-resistant subjects with an average age of 51.5, and an average BMI of 37.4 kg/m2. Participants were randomly assigned to receive a smoothie containing 22.5 grams of blueberry bioactives or a ‘placebo’ smoothie of equal nutritional value. Two smoothies were consumed every day for six weeks.
At the end of the study, 67 percent of people in the blueberry group experienced “at least a 10 percent or greater favorable change in insulin sensitivity, whereas only 41 percent of the placebo participants demonstrated this change”, stated the researchers.
On the other hand, no changes in BMI, body fat, or markers of inflammation were observed, said the Baton Rouge-based researchers.
“The bioactives in blueberries enhanced insulin sensitivity independent of any changes in inflammatory biomarkers or adiposity,” wrote Prof Cefalu and his co-workers. “This study is not conclusive, but it strongly suggests a need to further explore the cellular mechanism for the effect.
“In addition, our study suggests the need for studies of longer duration that will evaluate blueberries and their potential role in improving insulin sensitivity in an insulin-resistant human population,” they concluded.
The United States Highbush Blueberry Council (USHBC) prepared the freeze-dried whole blueberry powder used in this study. Funding was obtained from the USHBC, the NIH, and the National Center for Complementary and Alternative Medicine and the Office of Dietary Supplement.
Source: Journal of Nutrition