In a recent study published within the journal Food & Function, a team of European researchers explored the role of blackcurrant (BC) extracts in reducing blood sugar or glycemic levels after meals and investigated whether fruit fiber can enhance this effect. Their results indicate that while BC reduces glycemic levels immediately after meals, higher doses are not any simpler than lower doses, and fruit fibers don’t augment the effect.

Study: Acute effects of drinks containing blackcurrant and citrus (poly)phenols and dietary fibre on postprandial glycaemia, gut hormones, cognitive function and appetite in healthy adults: two randomised controlled trials. ​​​​​​​Image Credit: Created with the help of DALL·E 3

Background

The burden of type 2 diabetes (T2D), each by way of prevalence and associated mortality, has been rising globally. In Europe alone, one-fifth of adults are estimated to be prediabetic and will progress to T2D inside the following decade. Due to this fact, identifying effective interventions to stop this progression is a public health priority.

Individuals who often experience elevated levels of blood glucose after meals, also often called high postprandial glycemia, are at a better risk of developing T2D in addition to certain heart diseases. Dietary adjustments, particularly by including polyphenols and fruit fibers similar to pectins, may reduce postprandial glycemia and promote glycemic control in the long run. Scientists imagine it is because polyphenols slow the speed at which glucose is absorbed into the blood, and fruit fibers slow the speed at which the stomach empties.

In regards to the study

Researchers conducted two separate trials between May 2017 and January 2019.

First, they hypothesized that if combined, fruit fibers and polyphenol extracts can be simpler than either component individually in reducing blood glucose levels. This was tested in a trial called the GLU-FX study, where they examined the effect of BC and sweet orange (SO) polyphenol extracts on postprandial glucose levels, insulinemia, post-meal appetite, and gut hormone secretions.

Participants within the GLU-FX trial were randomized to a sequence of treatments, where they were assigned a placebo (0 mg polyphenols) in a single period and given three out of 4 test drinks through the remainder of the study. These drinks included (1) L-BC (800 mg polyphenols), (2) H-BC (1600 mg polyphenols), (3) L-SO (800 mg SO), and (4) H-Mix (800 mg BC and 800 mg SO). There was a ‘wash-out’ period of a minimum of one week between treatments.

Within the second trial, the GLU-MIX study, researchers hypothesized that combining fiber-rich citrus pulp and BC would cut back the world under the blood glucose curve (iAUC) between 0 and half-hour greater than a citrus pulp individually. They tested this by examining the effect of drinks containing only fiber and BC + fiber on postprandial glucose levels, insulinemia, post-meal appetite, and cognitive functioning. The drinks provided on this trial included (1) a control with no polyphenols or fiber, (2) 1.5 g total fiber (F), and (3) 800 mg BC and 1.5 g total fiber (BC + F).

In each trials, researchers collected blood for evaluation on the time participants drank the beverages and at different time points between ten minutes and two hours after consumption. Participants also filled up questionnaires with details about their mood and satiation levels at different time points and the way palatable the drink was 10 minutes after they consumed it. GLU-MIX participants also accomplished a cognitive battery test 45 minutes and 160 minutes after consumption and got a carbohydrate-rich meal 215 minutes after drinking the test beverages.

Participants were aged between 18 and 70 years, with a body mass index (BMI) between 18 and 35. Their good health was determined by the incontrovertible fact that none of them had cancer, allergies, sensitivities, or conditions similar to phenylketonuria. Individuals who had donated blood within the 12 months preceding the study or had medical tests with abnormal results were excluded, as were smokers and people with a history of alcoholism or substance abuse.

Findings

Within the GLU-FX trial, 29 participants accomplished the study, of whom 60% were female, and greater than half were white. On average, they were 37 years old. Researchers found that the L-BC beverage significantly reduced blood glucose levels in comparison with the placebo in the primary half-hour after consumption but not afterward.

Each L-BC and H-BC reduced blood insulin levels and C-peptide concentrations in comparison with the control in the primary half-hour, but not beyond. There have been no significant differences in mood and appetite scores. Participants did note that L-BC and H-blend were tougher to drink and that the L-SO drink had a more nice texture.

Within the GLU-MIX trial, 37 accomplished the trial, and participant characteristics were very just like the GLU-FX population. Researchers found that blood glucose levels were significantly reduced by the BC + F beverage in the primary half-hour after consumption. Similarly, BC + F was related to lower insulin levels and C-peptide concentrations.

The BC + F beverage also reduced response times and accuracy within the cognitive tests. There have been no significant differences in appetite, mood, or energy intake, but participants noted that they were thirstier after drinking BC + F. The test drinks were considered harder to eat and fewer nice than the control, and BC + F was considered more bitter.

Conclusions

This study aimed to evaluate whether combining dietary fiber and polyphenol-rich fruit extracts is simpler on blood glucose and insulin levels, gut hormones, mood, appetite, and cognitive function. Researchers found no evidence of a linear relationship between polyphenol dose and early postprandial glucose levels and no evidence that fiber-rich fruit extracts could enhance the effect of polyphenols.

Nonetheless, the authors caution against treating these findings as conclusive. The incontrovertible fact that only healthy individuals were included within the trial is a limitation, as these populations can clear circulating glucose from their bloodstream faster. The easy meals provided within the trial didn’t include various macronutrients, which could enhance the results of polyphenols on blood sugar levels. One other limitation was that individual participants didn’t receive every treatment.

Despite the constraints, this study provides interesting insights and avenues for further research. A key priority for future work is moving beyond healthy populations and exploring the role of polyphenols in reducing blood glucose levels in prediabetic populations.