These findings, published in the British Journal of Nutrition, add to the building science of polyphenols’ potential benefits in blood sugar management. It was funded partially by Canadian nutraceutical firm Atrium Innovations as part of its Polyphenols Projects initiative.
In this current study, researchers from Laval University in Quebec built on previous studies that have shown “a link between increased consumption of fruits and vegetables, particularly berries, and reduced incidence of type 2 diabetes,” they wrote.
They hypothesized that the consumption of strawberry and cranberry polyphenols improves insulin sensitivity and lipid profile, as well as reduces inflammatory and oxidative stress markers in overweight or obese humans.
A total of 41 overweight or obese adults (18 men and 23 post-menopausal women) were included in the study. The participants were divided into two groups, one supplemented with strawberry and cranberry polyphenols, and the other a control group.
The polyphenol drink contained 1.84g of a mixture of dry strawberry (Fragaria x ananassa Duch) and cranberry (Vaccinium macrocarpon L.) polyphenol extracts branded GlucoPhenol by Nutra-Canada. It provided an average daily dose of 333mg of polyphenols, and roughly equal to two servings of fresh fruit.
The control beverage was given pomegranate-derived red food color and flavor to mimic the polyphenol blend. Both were formulated in a single batch by Atrium Innovations.
Participants were asked to maintain their usual food habits and physical activity level. The consumption of berries, wine, polyphenol supplements, and all products containing berries or wine was also forbidden. Participants in both groups were asked to consume the assigned beverages daily for a 6-week period.
Results: Strawberry and cranberry polyphenols improved insulin sensitivity
The researchers found that insulin sensitivity increased in the supplement group compared to the control, and that the supplement group had a lower first-phase insulin secretion response measured by C-peptide levels during the first 30 minutes of the oral glucose tolerance test.
“The beverage rich in polyphenols prevented a further elevation in early-phase insulin release [and] prevented the overall increase of insulin secretion, suggesting that the improvement in insulin sensitivity after consumption of the SCP beverage may have precluded a further compensatory increase in insulin secretion,” the researchers wrote.
‘No significant effect on lipids’
The blend, however, had no significant effect on lipids and markers of inflammation and oxidative stress between the two groups.
“It would have been interesting to obtain muscle and adipose tissue biopsies to test whether SCP reduced inflammation in these tissues. Such biopsies may have also allowed us to ascertain the identity of the molecules involved in cellular insulin signaling,” they added.
Nonetheless, the present study suggested that the consumption of strawberry and cranberry polyphenols resulted in the improvement of insulin sensitivity and oral glucose test parameters. The researchers suggest that a longer-term intervention with larger populations will be necessary to confirm the results.
Source: British Journal of Nutrition
Published online ahead of print, doi:10.1017/S0007114517000393
Strawberry and cranberry polyphenols improve insulin sensitivity in insulin-resistant, non-diabetic adults: a parallel, double-blind, controlled and randomised clinical trial
Authors: Martine Paquette, et al.