Oat is among the food crops and ancient grains cultivated and consumed worldwide. It is gaining in popularity owing to its nutritional composition and multifunctional benefits of select bioactive compounds.
Beta-glucan is an important component of dietary fiber found in oat grains. It is the major active compound in oats with proven cholesterol-lowering and antidiabetic effects.
Oats also provide substantial levels of other bioactive compounds such as phenolic acids, tocols, sterols, avenacosides, and avenanthramides.
The consumption of oats has been determined to be beneficial for human health by promoting immunomodulation and improving gut microbiota.
In addition, oat consumption assists in preventing diseases such as atherosclerosis, dermatitis,
While much has been published in relation to oat nutrients and oat fibers and their impact on major diseases, the oat industries and consumers may benefit from greater knowledge and understanding of clinical effects, range of occurrence, distribution, therapeutic doses and food functional attributes of other oat bioactives such as avenanthramides and saponins as well as other anti-inflammatory agents found in the cereal.
This review focuses on the various studies relevant to the contribution of the consumption of oats and oat-based products in preventing human diseases and promoting human health.
Oats for Cardiovascular Diseases
Cardiovascular diseases (CVD) are among the leading causes of human deaths worldwide, and a study has shown that dietary risk is the major contributor for CVD. Based on National Health Interview Survey data, in 2017, 485.6 million people were under the prevalence of CVD worldwide, and this number increased by 28.5% in 10 years [105]. Mathers and Loncar (2006) [106] projected that CVD would claim 23.3 million people’s lives by 2030.
High levels of serum cholesterol and low-density lipoproteins (LDL) are known to increase the risk of CVD. The consumption of oats, however, was shown to reduce serum total cholesterol and LDL cholesterol, thereby reducing the risks of CVD [10,43,107,108,109]. A dietary approach, has been recommended as one of the most practical approaches for the treatment of LDL cholesterol [1,110]. Studies show that beta-glucan-rich oats or oat-based products in a diet significantly decrease the blood lipid profile and blood pressure by regulating insulin metabolism in a mild hypercholesterolemia subject [22,23,24,32,36]. Viscous OBG has been attributed to slowing the absorption of macronutrients in the digestive tract, which lowers postprandial blood glucose and the insulin response, thereby reducing blood pressure [111,112]. A dose-response relationship study in a mouse model showed that a higher amount of OBG is accompanied by a higher reduction of serum cholesterol level [25]. However, in one of the studies where healthy young men were fed with oat gum containing 9 g OBG daily for 14 days, there was no significant difference in the reduction of total serum cholesterol, LDL cholesterol, HDL cholesterol, and triglyceride concentrations between test group or control group. The authors suggested that the cholesterol-lowering property of oat bran should be measured not by the beta-glucan content but by the solubility and viscosity of OBG [35]. A study done on hypercholesterolemic subjects also supports this conclusion [113]. The amount and molecular weight (MW) of OBG that solubilizes in the intestine together with other compounds present in an oat product and their association also determine the cholesterol-lowering property [114,115].
Unrefined and whole oat-based products are more effective in lowering cholesterol as compared to processed oat products where oat tissues are highly disrupted. Studies suggest that for a similar amount of OBG, liquid-based foods are more effective than solid or semi-solid food. Hydrothermal processing is found to increase the extractability and reduce the solubility of OBG. Extracted OBG could also be depolymerized when incorporated into the food products [115]. β-glucanase contained in wheat also deactivates OBG in bakery products containing wheat during the fermentation process [114].
The cholesterol-lowering property of OBG is mainly mediated through the formation of a viscous layer in the small intestine, thereby inhibiting the uptake of cholesterol and increasing the excretion of bile acids by preventing its reabsorption. The inhibition of bile acid reabsorption stimulates the synthesis of bile acids from the available cholesterol, which in turn reduces the circulating LDL cholesterol [1,30,116].
It has also been proposed that soluble fiber helps in the reduction of cholesterol synthesis through an alteration in serum concentrations of hormone or short-chain fatty acids (SCFA)—acetate, propionate, and butyrate—which ultimately affects lipid metabolism. SCFA butyrate concentration significantly decreases the de novo synthesis of cholesterol in isolated rat hepatocytes [33]. Another study reported an increase of serum acetate and propionate levels following the consumption of oat bran diet, and the authors suggested that the SCFA response might have contributed to the cholesterol lowering effect [37].
Because of the number of studies and evidence supporting the beneficial roles of OBG, the United States Food and Drug Administration (FDA) approved the use of health claims on oat-based products, contributing to lowering the risk of CVD if consumed at the rate of 3 g per day of beta-glucan and if the food product contributes 0.75 g of beta-glucan per serving [117]. Similarly, Health Canada, the European Food Safety Authority, Food Standards in Australia and New Zealand, and the Ministry of Health in Malaysia have also approved health claims for oats related to the association between OBG and cholesterol [10].
In addition to beta-glucan, proteins and lipids in oats also contribute to lowering cholesterol [26,27].
Oat are rich in protein, ranging between 12 to 20% of oat groats. Oat proteins are high in albumins and globulins and low in prolamins. Prolamins have a lower lysine content than albumins and globulins [118],
and hence oat protein has a higher biological value than other cereals with high prolamin content, and the Limited Amino acid (LAA) score of oat flour is 66.9, whereas wheat flour’s is 49.8 [119].
Oat protein may help to decrease the serum total and LDL cholesterol levels because they have low Lysine/Arginine and Methionine/Glycine ratios [26].
Favoring the excretion of fecal steroid, which would lead to a hepatic conversion of cholesterol into bile acid and the elevation in the expression of the LDL receptor, are possible mechanisms behind the cholesterol-lowering property of oat protein [120]
. Oat is a good source of dietary fats, as the lipid content in oat groats ranges from 5 to 9%, which is the highest among cereal grains [121]
. Tong et al. (2014) [31] reported that the consumption of oat oil by rats promoted the excretion of fecal lipids and bile acids. However, more evidence is required to confirm the cholesterol-lowering property of oat oil, as not all studies are in agreement [122].
Foods. 2021 Oct 26;10(11):2591. doi: 10.3390/foods10112591
A Review of Health-Beneficial Properties of Oats
Devendra Paudel 1, Bandana Dhungana 2, Melanie Caffe 2, Padmanaban Krishnan 1
,*बीटा-ग्लुकन व्यतिरिक्त, ओट्समधील प्रथिने आणि लिपिड्स देखील कोलेस्टेरॉल कमी करण्यास हातभार लावतात [26,27].
