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Wholegrain cereal and their potential effects on health
By Dr Shashikala (UCSI University)
There is a large body of evidence to suggest that the inclusion of wholegrains in the diet is beneficial for human health 1,2. Wholegrain cereals, i.e., grains that include the bran, germ, and endosperm, are good sources of vitamins, minerals, dietary fiber, and phytochemicals 1,2. These compounds are mostly present in the outer kernel layers, i.e., the pericarp and aleurone, which are typically removed when the grain is milled, and cereal flour is produced 1.
The intake of high levels of dietary fiber, vitamins and minerals, and important phytochemicals like indoles, polyphenols, carotenoids, and phytosterols is responsible for the potential health-promoting benefit of regular cereal wholegrain consumption 1,2. The relationship between the regular consumption of whole meal products and a reduced risk of non-communicable chronic diseases has been previously established 2,3. The specific food structure and dietary fiber content, combined with the antioxidant and anti-carcinogenic effects of numerous compounds (especially polyphenolic compounds), are well recognized compound in the risk reduction of cardiovascular diseases, obesity, diabetes, and certain types of cancer 1,3.
The benefits of bioactive small molecules
Most research has focused on the health effects of the major constituents of wholegrains (e.g., dietary fiber) 1. However, bioactive small molecules also play a role in the benefits of wholegrain consumption. Polyphenols, for example, are compounds that possess one or more aromatic rings, with one or more hydroxyl groups, and can be categorized into one of five groups (flavonoids, stilbenes, phenolic acids, coumarins, and tannins) 1. Phenolics act as singlet oxygen quenchers and free radical hydrogen donors, which have a protective effect on cell constituents against oxidative damage 4. Among them, anthocyanins are a group of water-soluble flavonoids and are responsible for red, violet, and blue colors in fruits, vegetables, and cereal grains 5,6. Anthocyanins have demonstrated in vitro antioxidant potential, and consumption of foods high in anthocyanins has been linked to a lower risk of chronic diseases 5.
Several commercially relevant cereal grain families contain some distinctly coloured varieties 7. These colours often stem from anthocyanins present in the kernels as one of the primary natural pigments. Wheat, maize, sorghum, barley, rice, and millet all have varieties with significant amounts of anthocyanins in the outer layers of the kernel. Coloured grains rich in anthocyanins have been identified as promising ingredients for the development of wholegrain functional foods.
The role of antioxidants
Free radicals and other reactive species produced in the body under physiological conditions play important roles in regulatory pathways and processes 8. Production of free radicals and other reactive species is generally regulated by cellular defence systems, at a controlled rate. However, if the antioxidant defence system is disturbed and is not working sufficiently, an imbalance occurs in cells towards oxidative stress 2,8. This state has been linked to the development of several diseases including cancers, cardiovascular diseases, hypertension, inflammation, and diabetes 3,8,9.
Dietary antioxidants can mitigate this oxidative stress through several mechanisms, depending on the structure of the molecule. Antioxidants may be efficient free radical scavengers, singlet oxygen quenchers, peroxide inactivators, metal ion chelators, and/or inhibitors of pro-oxidative enzymes 3,8,9. Many phytochemicals in our diet act as antioxidants. Anthocyanins are one of these phytochemicals. Indeed, anthocyanins have even demonstrated a greater antioxidant activity than vitamins C and E in vitro 10. However, the exact mechanism that governs their antioxidant is still under debate and requires further studies 11. Despite this mechanistic uncertainty, numerous in vivo and in vitro studies have demonstrated antioxidant acticities of anthocyanins 9,11.
Wholegrain may reduce risk of chronic disease
Consumption of wholegrain cereals has been shown to protect against obesity, diabetes, cardiovascular disease, and cancer 1,3. Part of these health benefits can be ascribed to the high dietary fiber content. Although attempts have been made to investigate the specific role of the individual compounds, the specific health-promoting effect of each component has not yet been fully elucidated 2,3. According to Malin et al. (2018), the mechanism of action through which wholegrains lower the diabetes risk involves a reduced post-prandial blood glucose and peripheral insulin resistance that are statistically linked to enhanced metabolic flexibility 16. This mechanism is a property of soluble/viscous fiber.
However, the major wholegrain intake worldwide is based on wholegrain wheat, which is low in this type of fiber. Randomized controlled trials acertain also that the consumption of wholegrains improve blood glucose control, may reduce fasting insulin levels, and reduces insulin resistance 9,12,13, indicating that a wholegrain diet may increase insulin sensitivity, which controls blood sugar levels. The physical nature of the wholegrain, as well as its level of processing, can affect the metabolic response to its intake. An early study suggested that the insulin responses increase as follows: Wholegrains < cracked grains < coarse flour < fine flour 15, therefore, there is an inverse correlation between the forms of wholegrain and the impact on glucose metabolism.
There are several mechanisms mentioned by which consumption of wholegrains may contribute to weight management. Firstly, the fact that wholegrain products possess a reduced energy density (kilocalories/unit weight). Secondly, their higher content in non-digestible carbohydrates compared to refined cereal foods 16,12, which increases satiety and therefore, the feelings of fullness 13.
Choose wholegrain foods
The consumption of wholegrains and wholegrain products has gained popularity because of their potential protection against cancer. This antioxidant effect is due to their phytochemicals that combat oxidative stress 17. Wholegrain phytochemicals can regulate cellular signal transduction pathways and hence affect cancer cell behaviors such as proliferation, apoptosis, and invasion 18. Bran antioxidants may concur to cellular protection while preventing oxidation damage at the cellular level. The potential of phenolic acids to inhibit cancer was attributed to the reduction in oxidative damage to cells and cell components 42,19,20.
Cereal grains represent one of the major sources of human food and nowadays, their production has increased to fulfill the needs of the world’s population. Among wholegrains, wheat and rice are the most popular and contribute significantly to the human diet. Wholegrains possess great nutritional and bioactive properties due to their fractions, bran and germ, that comprise unique health-promoting bioactive components. The evidence of health benefits in human intervention studies, as well as a World Health Organization report for 2012–2016, supports the dietary consumption of wholegrains and whole-grain foods.
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