Impact Of Blackcurrant and Citrus Extracts in the Prevention of T2D
Type 2 diabetes (T2D) has been on the rise globally, both in terms of its prevalence and associated mortality. In Europe, an estimated one-fifth of adults are deemed prediabetic, making them susceptible to transitioning to full-blown T2D within the next decade. In light of this looming public health crisis, identifying effective interventions for preventing the progression from prediabetes to T2D is of utmost importance.
One such avenue of exploration is the potential role of blackcurrant (BC) and citrus extracts in mitigating postprandial glycemia, which is the elevated blood sugar levels experienced after meals. This article delves into the recent study published in the journal Food & Function, where European researchers examined the acute effects of blackcurrant and citrus extracts, as well as dietary fiber, on postprandial glycemia, gut hormones, cognitive function, and appetite in healthy adults.
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The Growing Diabetes Epidemic
The burden of T2D has reached alarming proportions globally. Europe alone grapples with a substantial prediabetic population, estimated at one-fifth of its adult citizens, who are at risk of progressing to T2D within the next decade.
Managing this escalating health crisis calls for effective interventions to prevent the onset of T2D. People who regularly experience elevated blood glucose levels after meals, known as high postprandial glycemia, are at a heightened risk of developing T2D and certain heart diseases. Fill out this form to check if you or a friend qualify for CGMs.
Dietary adjustments, particularly incorporating polyphenols and fruit fibers, such as pectins, have been explored as a means to reduce postprandial glycemia and promote long-term glycemic control. Scientists posit that polyphenols can slow the absorption of glucose into the bloodstream, while fruit fibers can delay the rate at which the stomach empties, contributing to more stable blood sugar levels.
Diving into the Study
The study in question, conducted by European researchers between May 2017 and January 2019, consists of two distinct trials that aimed to unravel the potential benefits of blackcurrant (BC) and sweet orange (SO) polyphenol extracts, as well as dietary fiber, on postprandial glycemia and related factors.
Trial 1: The GLU-FX Study
In the GLU-FX study, the researchers set out to explore whether combining fruit fibers and polyphenol extracts could produce a more pronounced reduction in blood glucose levels than each component individually.
This trial examined the effects of Blackcurrant and SO polyphenol extracts on postprandial glucose levels, insulin levels, post-meal appetite, and gut hormone secretions.
Participants in this trial were randomly assigned to a sequence of treatments, which included a placebo (0 mg polyphenols) in one period and three out of four test drinks in the remaining sessions.
The test drinks consisted of: (1) Low-dose BC (800 mg polyphenols), (2) High-dose BC (1600 mg polyphenols), (3) Low-dose SO (800 mg SO), and (4) a combination of Blackcurrant and SO (800 mg each). A ‘wash-out’ period of at least one week separated each treatment.
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Trial 2: The GLU-MIX Study
In the GLU-MIX study, the researchers posited that combining fiber-rich citrus pulp and Blackcurrant could result in a greater reduction in the area under the blood glucose curve (iAUC) between 0 and 30 minutes when compared to citrus pulp alone.
The trial involved examining the effects of drinks containing only fiber and a combination of BC and fiber on postprandial glucose levels, insulin levels, post-meal appetite, and cognitive functioning. The test drinks for this trial included: (1) A control beverage with no polyphenols or fiber, (2) 1.5 grams of total fiber (F), and (3) 800 mg BC combined with 1.5 grams of total fiber (BC + F).
In both trials, blood samples were collected at various time points, including the time of beverage consumption and subsequent measurements taken between ten minutes and two hours after ingestion.
Participants also completed questionnaires regarding mood, and satiation levels at various intervals, and assessed the palatability of the drink 10 minutes after consumption. In the GLU-MIX study, participants underwent cognitive battery tests at the 45-minute and 160-minute marks post-consumption, followed by the consumption of a carbohydrate-rich meal at 215 minutes after drinking the test beverages.
The participants in these trials were aged between 18 and 70, with a body mass index (BMI) ranging from 18 to 35. Their inclusion was contingent on their overall good health, as individuals with cancer, allergies, sensitivities, phenylketonuria, a history of alcoholism or substance abuse, or those who had donated blood in the year before the study began were not considered for inclusion. Additionally, smokers and individuals with medical test results indicating abnormalities were also excluded.
Insights and Findings
In the GLU-FX trial, involving 29 participants, the majority of whom were female and more than half identified as white, researchers discovered that the low-dose Blackcurrant beverage significantly reduced blood glucose levels in the first 30 minutes after consumption when compared to the placebo.
However, this effect did not persist beyond the initial half-hour. Both the low-dose and high-dose BC beverages reduced blood insulin levels and C-peptide concentrations in the first 30 minutes compared to the control.
Interestingly, there were no significant differences in mood and appetite scores among the participants. Notably, participants reported that the low-dose BC and the BC-SO blend were more challenging to consume, and the low-dose SO drink had a more pleasing texture.
In the GLU-MIX trial, which involved 37 participants with characteristics similar to those in the GLU-FX study, Blackcurrant+ F significantly reduced blood glucose levels in the first 30 minutes after consumption. Moreover, BC + F was associated with lower insulin levels and C-peptide concentrations, suggesting a positive impact on glycemic control.
Interestingly, the BC + F beverage also affected cognitive function, as it reduced reaction times and accuracy in cognitive tests. However, there were no significant differences in appetite, mood, or energy intake, although participants did report feeling thirstier after consuming the BC + F beverage.
It is noteworthy that the test drinks, particularly the BC + F combination, were considered more challenging to consume and less pleasant than the control. Additionally, the BC + F combination was perceived as more bitter in taste.
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Conclusive Remarks and Future Directions
While this study sought to investigate whether combining dietary fiber and polyphenol-rich fruit extracts had a more pronounced impact on blood glucose and insulin levels, gut hormones, mood, appetite, and cognitive function, it did not provide evidence of a linear relationship between polyphenol dosage and early postprandial glucose levels. Furthermore, there was no indication that fiber-rich fruit extracts could enhance the effect of polyphenols.
However, it is crucial to note that the study has its limitations. The inclusion of only healthy individuals may limit the generalizability of the findings, as these individuals tend to clear circulating glucose from their bloodstream more rapidly.
The study also employed relatively simple meals, which did not encompass a wide variety of macronutrients, potentially affecting the ability of polyphenols to influence blood sugar levels. Additionally, the fact that individual participants did not receive every treatment represents another limitation.
Despite these limitations, this study offers intriguing insights and opens doors for further research. A critical priority for future investigations lies in expanding beyond healthy populations and exploring the role of polyphenols in reducing blood glucose levels in prediabetic individuals.
Such research could be instrumental in developing strategies to combat the rising tide of T2D and its associated complications. While the journey is ongoing, this study marks a significant step toward understanding the potential of blackcurrant and citrus extracts in the prevention of T2D, offering hope for a healthier and more diabetes-resistant future.
