Nutrition in a Nutshell: Unravelling the Health Benefits of Bioactive Compounds Found in Nuts
By Mena Farazi
According to Diabetes Australia, over 300 Australians are diagnosed with diabetes daily, with the majority being type 2. Individuals with type 2 diabetes have elevated blood sugar levels and are at a higher risk of developing chronic diseases such as heart disease and kidney disease.
After a meal, it's normal for blood sugar levels to rise. Enzymes such as α-amylases and α-glucosidases rapidly digest carbohydrates to produce smaller sugar units that are absorbed from the small intestine into the blood, leading to elevated sugar levels. However, individuals with diabetes are unable to effectively respond to blood sugar spikes. Thus, the inhibition of these enzymes, to slow down the rate of carbohydrate digestion and glucose absorption, is a critical step in regulating blood sugar spikes.
Some anti-diabetic drugs, such as acarbose, are used to inhibit α-amylase and α-glucosidase to control blood sugar levels, and it has been reported that various plant extracts and bioactive compounds can also inhibit α-glucosidase activity. However, acarbose can have undesirable side effects due to excessive enzyme inhibition and an overflow of undigested carbohydrates into the colon. As a consequence, individuals may experience bloating, cramps, flatulence, and discomfort in the abdominal region.
Nut consumption is recommended in dietary guidelines worldwide because of its health benefits. Studies have shown an association between low nut consumption and the risk of developing diabetes. Bioactive compounds from nuts, including polyphenols, may help to lower blood sugar spikes after a meal. One action of some polyphenols is to lower blood sugar spikes in the same way as acarbose.
PhD Candidate Mena Farazi and team reviewed the current literature to assess the inhibition of human α-glucosidase activity by bioactive compounds extracted from nuts in vitro; however, the search included all sources of α-glucosidase and was not confined only to human enzymes.
Our research found:
- No studies have examined the inhibitory effect of nut extracts on human α-glucosidase, and only two out of the 15 included studies used mammalian (rat) α-glucosidase.
- Bioactive extracts from nuts are potent inhibitors of yeast α-glucosidases.
- Where yeast and rat enzymes can be compared, it is clear that nut extracts inhibit yeast α-glucosidase more effectively than rat α-glucosidase, which may lead to overestimation when predicting effects in vivo based on data from the yeast enzyme.
- Yeast α-glucosidase is poorly inhibited by acarbose, a positive control that is used clinically since it is highly effective at inhibiting human α-glucosidase activities, and acarbose is always a stronger inhibitor of the mammalian α-glucosidase compared to the yeast enzyme.
Although extracts from nuts may inhibit yeast α-glucosidase, it is never clear whether these compounds can also inhibit human (or rat) α-glucosidase until the appropriate in vitro studies have been done. Therefore, the lack of studies on human α-glucosidase, and the growing attention to nuts as an important component of a healthy diet with the potential to reduce type 2 diabetes risk, highlights the need for future research to evaluate the inhibitory effect of extracts from nuts on human α-glucosidase activities.
Technical terms:
In vitro studies: Experiments or investigations conducted outside of a living organism.
In vivo studies: Research conducted within a living organism, typically using an animal model or human subjects.
By Mena Farazi
Mena Farazi is a PhD Candidate in the Department of Nutrition, Dietetics and Food at Monash University. Her research is focused on the inhibitory effect of polyphenol extracts from nuts such as walnuts and almonds on carbohydrate absorption and digestion to lower blood sugar level after a meal.
Publication information
Mena Farazi, Michael J. Houghton, Margaret Murray and Gary Williamson, “A systematic review of the inhibitory effect of extracts from edible parts of nuts on α-glucosidase activity”, Food Funct., 2023, Advance Article. https://doi.org/10.1039/D3FO00328K
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