A recent narrative review published in the Nutrients Journal, researchers examine evidence supporting the use of adzuki beans (Vigna angularis) as a dietary supplement for the prevention and treatment of type 2 diabetes (T2D).
Study: The potential of adzuki bean (Vigna angleis) and its bioactive compounds in the treatment of type 2 diabetes and glucose metabolism: A narrative review. Image source: Hanasaki/Shutterstock.com
There are several research gaps in the current literature when it comes to evaluating the effects of consuming adzuki beans for the prevention and treatment of T2D in humans.
Most evidence of their usefulness for T2D comes from animal studies, and these have yet to identify the underlying mechanisms through which adzuki beans impact T2D-related outcomes.
In addition, rodent studies have used only male animals; as a result, the antidiabetic effects of adzuki bean supplementation in females remain unclear.
Furthermore, research has not identified the chemical and biochemical properties of functional (bioactive) compounds in adzuki beans.
Overall, the evidence supporting the use of adzuki bean supplementation for T2D prevention and addressing related outcomes in obesity and dyslipidemia is not conclusive.
The adzuki bean (Vigna angularis) is a legume with a low glycemic index (=26); thus, it may be a useful addition to the diabetic diet.
Some notable bioactive compounds in adzuki beans include kaempferol, catechins, anthocyanins, saponins, and phytic acid; in addition, proteins/peptides, polyphenols, and polysaccharides are to be considered.
China is the largest producer of adzuki beans in Asia, although they are consumed in several other Asian countries, including Japan, as a whole, as sweetened paste, in soup, etc. They are also used in commercial food products.
However, scientific investigations are needed to determine the dosage at which its consumption can offer antidiabetic health benefits, and its bioactive compounds and mechanisms of action contribute to the prevention and treatment of type 2 diabetes.
For their narrative review, the researchers extensively searched the Scopus and PubMed databases to identify studies in English language involving the use of adzuki beans for the treatment of T2D based on an evaluation of two key diabetes risk factors: obesity and dyslipidemia, in human, animal, and in vitro studies.
The Role of Adzuki Beans in Diabetes Treatment
Thirteen animal and two in vitro studies have examined the health benefits of adzuki beans in people with diabetes, and only one study has examined their effects in humans.
In diabetic mice with hyperglycemia, a T2D-related outcome, the consumption of adzuki bean flour improved glucose tolerance, blood sugar levels, and insulin sensitivity.
In male KK-Aj mice with T2D, hot water extracts from adzuki beans containing polyphenols lowered blood sugar levels, as reported by Itoh et al.
Compared to controls receiving 500 mg of cellulose/kg body weight (BW)/day, diabetic mice receiving a higher dose of adzuki bean hot water extract (500 mg) showed significantly lower blood sugar in weeks two, three, five, and six, showing more significant antidiabetic effects.
These effects were attributed to polyphenols in adzuki beans. Similarly, adzuki bean polysaccharides improved glucose homeostasis and recovery of pancreatic islet cells in rodents in a dose-dependent manner.
Furthermore, animal studies examined the effects of food processing on the content of bioactive compounds in adzuki beans, including steaming, extrusion cooking, and sprouting.
They found that while steaming decreased the ability of adzuki bean flour to address T2D outcomes, extruded cooked beans had better antidiabetic benefits than raw adzuki beans.
Raw adzuki beans had higher total phenol and flavonoid content, while cooked extruded adzuki beans had higher polysaccharide and protein content as well as higher α-glucosidase inhibitory activity, facilitating glucose release into the bloodstream gradually.
Sprouting adzuki beans also increased their content of antidiabetic polyphenols.
In addition, the researchers compared the effect of adzuki beans with sulfonylurea and metformin, oral medications for the treatment of type 2 diabetes.
A 500 mg hot water extract from adzuki beans/kg BW in mice had better antidiabetic effects in healthy and diabetic subjects than sulfonylurea.
However, there was no significant difference in liver glycogen content in diabetic rats receiving adzuki bean polysaccharides (400 mg/kg BW/day) or metformin.
Adzuki bean polysaccharides modulated T2D-related outcomes by activating the PI3K/AKT signaling pathways, which regulate glucose metabolism and insulin responses, thus positively affecting pancreatic and liver function.
The human study also showed that T2D indicators in recipients of extruded adzuki beans showed similar improvement to those receiving a traditional low-glycemic index diet for T2D treatment.
Similarly, various compounds derived from adzuki beans had different effects on serum lipid levels.
These varied depending on the type of adzuki bean compound used, dosage and duration of supplementation, and the methods used in processing.
In summary, there is enough evidence to support the use of adzuki bean supplementation for T2D outcomes, which are similar or better than T2D medications and compliance with low glycemic index diets.
However, further research is needed to investigate the impact of adzuki bean supplementation on T2D-related outcomes in human subjects, particularly regarding the:
- Impact of food processing on the antidiabetic potential of bioactive compounds in adzuki beans;
- How adzuki beans modulate serum lipid levels;
- Their antioxidant benefits; and
- Their role in modulating the gut microbiota.