A study published in the journal Nutrition & Diabetes reveals that increasing the intake of flavonoid-rich foods can reduce the risk of developing type 2 diabetes.
Study: Higher habitual intakes of flavonoids and flavonoid-rich foods are associated with a lower incidence of type 2 diabetes in the UK Biobank cohort. Image Credit: DIVA.photo / Shutterstock
Background
Type 2 diabetes has become a significant public health concern because of its steadily increasing prevalence worldwide. Currently, 415 million people are living with diabetes, and more than 4 million deaths are associated with this condition globally.
Certain modifiable risk factors, such as obesity and overweight, are associated with the development of type 2 diabetes, which subsequently increases the risk of developing several health complications, including cardiovascular disease, kidney disease, dementia, and certain cancer types.
A higher intake of plant-based diet is known to reduce the risk of type 2 diabetes. Plants are rich sources of various polyphenolic compounds with different bioavailability and bioactivity. Flavonoids are a class of polyphenolic compounds grouped into six main subclasses: flavanones, flavones, flavan-3-ols, flavonols, anthocyanins, and isoflavones.
Evidence from randomized controlled trials (RCTs) indicates that higher intake of flavonoids is associated with increased insulin sensitivity, reduced insulin resistance, and improved blood lipid profile.
In this study, scientists have investigated the association between a flavonoid-rich diet and incident type 2 diabetes in a large-scale UK population.
Study design
A total of 113,097 UK Biobank participants were enrolled in the study. The UK Biobank is a large-scale, population-based prospective cohort study of more than 500,000 adult participants recruited from the UK between 2006 and 2010.
Two or more 24-hour dietary assessments obtained from the participants were analyzed using the US Department of Agriculture databases to calculate flavonoid intakes. Ten flavonoid-rich food items were selected based on mean daily intakes (daily servings). A Flavodiet Score (FDS) was calculated by summing the total number of servings consumed across the ten selected food items.
Appropriate statistical analyses were conducted considering potential confounding factors to determine the association between dietary exposures and incident type 2 diabetes.
Important observations
During the average study follow-up period of 12 years, 2,628 incident type 2 diabetes cases were identified.
A comparatively higher intake of flavonoid-rich diet was observed among female participants, older participants, physically active participants, or those with higher educational backgrounds.
The average total flavonoid intake per day was 805.7 milligrams. Among different subclasses, polymers, including proanthocyanidins and flavan-3-ols, contributed 67% and 22% of total flavonoid intake, respectively. Tea intake was the primary source for these two subclasses.
The lowest contributing subclass to total flavonoids was flavones, derived predominantly from peppers.
Association between flavonoid intake and incident type 2 diabetes risk
The analysis adjusted for demographic and lifestyle characteristics of participants revealed that a higher FDS (six servings of flavonoid-rich foods per day) is associated with a 28% lower risk of incident type 2 diabetes, as compared to lower FDS (one serving of flavonoid-rich foods per day).
The dose-response analysis revealed that increasing one serving per day of flavonoid-rich foods is associated with a 6% lower risk of incident diabetes.
Regarding specific flavonoid-rich food items, the study found that higher intakes of black or green tea, berries, and apples are associated with 21%, 15%, and 12% lower risk of incident type 2 diabetes, respectively.
Regarding specific flavonoid subclasses, higher intakes of anthocyanins, flavan-3-ols, flavonols, flavones, polymers, and proanthocyanidins were found to associate with a 19%, 26%, 28%, 19%, 26%, and 27% lower risk of incident diabetes, respectively.
Mechanistic analysis
The study analyzed several potential biomarkers related to type 2 diabetes to identify the biological mechanisms responsible for the observed associations.
The mediation analysis identified body mass index (BMI), insulin-like growth factor 1 (IGF-1), C-reactive protein, cystatin C, urate, gamma-glutamyl transferase (GGT), and alanine aminotransferase (ALT) as potential mediators.
Specifically, the findings indicated that the beneficial effects of a flavonoid-rich diet on body weight management, glucose metabolism, basal inflammation, and kidney and liver functions are partly responsible for the reduction in type 2 diabetes risk observed in the study.
Study significance
The study finds that flavonoid-rich foods can significantly reduce the risk of type 2 diabetes by regulating obesity, glucose metabolism, inflammation, kidney function, and liver function.
Existing literature indicates that flavonoids, especially anthocyanins, flavan-3-ols, and flavonols, can exert anti-diabetic effects by improving insulin secretion and signaling and facilitating glucose transportation and metabolism.
As mentioned by the scientists, the study population includes middle-aged British adults, which restricts the generalizability of findings to other non-European populations.
Overall, this study supports the current recommendation to increase the intake of fruits, especially berries and apples, to reduce type 2 diabetes risk.
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