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 Table of Contents  
REVIEW ARTICLE
Year : 2016  |  Volume : 5  |  Issue : 1  |  Page : 9-17

Oats: A multi-functional grain


1 Principal Nutrition Manager, Marico Ltd, Mumbai, India
2 Senior Nutrition Officer, Marico Ltd, Mumbai, India
3 Research Officer, Marico Ltd, Mumbai, India

Date of Web Publication14-Jun-2016

Correspondence Address:
Purvi Varma
Marico Limited, Marks Office, Plot No. 23/C, Mahal Industrial Estate. Mahakali Caves Road. Landmark: Before Paper Box Factory, Opp Andhra Bank and Travellers Inn Hotel. Andheri (E), Mumbai - 400093, Maharashtra
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/2250-3528.183984

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  Abstract 

Oats are predominantly a European and North American crop, as they have cool moist climate; Russia, Canada, the United States, Finland, and Poland are leading oat producing countries. Oats have been used as livestock and human foods since ancient times. Oats (Avena sativa) is a class of cereal grain essentially grown for human consumption as well as for livestock fodder. Food industry fundamentally alter agricultural commodities into foods making it edible, palatable as well as appealing; by innumerable physical and chemical operations increasing shelf-life, bioavailability of the nutrients, stabilizing colour, flavour along with increase in the economic value of the grain. Recent observational and human interventional studies indicate that oats can have an impact on various non-communicable diseases like cardiovascular disease, diabetes; obesity and hypertension etc. Therefore it is important to increase awareness of oats and its health benefits among individuals thereby encouraging them to increase the frequency of oats in the diet. In the year 1997, USFDA approved the use of a health claim "3g/day of oat Beta- glucan may help lower blood total and low-density lipoprotein (LDL-C) cholesterol". Over all consumption of oats has increased in the recent years due to its nutritional benefits; presence of Beta-glucan, antioxidants like Avenanthramides, vitamin E (tocotrienols and tocopherols).

Keywords: Adiposity, cardiovascular disease, weight loss


How to cite this article:
Varma P, Bhankharia H, Bhatia S. Oats: A multi-functional grain. J Clin Prev Cardiol 2016;5:9-17

How to cite this URL:
Varma P, Bhankharia H, Bhatia S. Oats: A multi-functional grain. J Clin Prev Cardiol [serial online] 2016 [cited 2018 Oct 16];5:9-17. Available from: http://www.jcpconline.org/text.asp?2016/5/1/9/183984


  Introduction Top


The burden of chronic diseases is rapidly increasing worldwide. Almost half of the total chronic disease deaths are attributable to cardiovascular diseases (CVDs); obesity and diabetes are also showing worrying trends, not only because they already affect a large proportion of the population, but also because they have started to appear earlier in life. A systematic analysis in Global Burden of Disease Study revealed that the US had the highest number of the obese people worldwide (13%) in 2013, while China and India together accounted for 15% of the world's obese population, with 46 million and 30 million obese people, respectively . [1]

It is clear that the earlier labeling of chronic diseases as "diseases of affluence" is increasingly a misnomer, as they emerge both in poorer countries and in the poorer population groups in richer countries. This shift in the pattern of disease is taking place at an accelerating rate; furthermore, it is occurring at a faster rate in developing countries than it did in the industrialized regions of the world half a century ago. This rapid rate of change, together with the increasing burden of disease, is creating a major public health threat which demands immediate and effective action. With lifestyle disorders forcing more and more people to reel under excess body weight, even relatively younger people are developing joint disorders and knee pain. Excessive weight is associated with a series of health problems, including blood pressure, diabetes, and cardiovascular ailments. [2]

Experts have pointed that the phenomenon in South Asians has characteristic features - high prevalence of abdominal obesity, with more "intra-abdominal and truncal subcutaneous adiposity."

Weight loss has beneficial effects on blood pressure, lipids and glucose control, and weight loss in the range of 5-10% of initial weight that can confer significant improvement in these variables. In population studies, dietary factors, such as consumption of a vegetarian diet or a diet high in cereal fiber, fruits, and vegetables, also appear to be associated with reduced risk for hypertension, dyslipidemia, and CVD itself. Identification of such factors has stimulated considerable research effort directed toward the prevention of CVD and its risk factors through diet modification. In many circumstances, dietary interventions have been shown to have salutary effects on hypertension and hyperlipidemia. Oats (Avena sativa) is a class of cereal grain essentially grown for human consumption as well as for livestock fodder. [3]

Complex diets have shown to impart beneficial results in weight reduction and also in other diseases' management. It remains possible that particular classes of food or individual foods can confer specific benefit. Sometimes, it is difficult to bring about broader dietary changes in the diet; in such cases, it is preferable to introduce individual diet constituents which may bring about a major change. One such possible constituent is oats, a whole-grain cereal that is rich in soluble fiber. The effects of oats on lipid metabolism are well documented, and there is a growing body of literature to suggest that oats also lower blood pressure or help prevent CVD. Population studies suggest that diets rich in oats or other foods containing soluble fiber are associated with lower levels of blood pressure or rates of coronary disease. Oat or oat fiber consumption has been shown to reduce postprandial glucose and insulin concentrations, and the reduction in insulin concentration may provide a mechanism by which blood pressure could be reduced in response to oats consumption. [4]

New insights about the potential benefits of oats have emerged over the past 10 years. More recent data indicate that including oats and oat-based products as part of a lifestyle management program may confer health benefits that extend beyond total cholesterol and low-density lipoprotein (LDL) cholesterol reduction.

Oats remain an important cereal crop in the developing world, and the most popularly cultivated species is Avena sativa L. Compared to other cereals, oats require a cool and moist climate. It requires more moisture for its growth. Oats is predominantly grown in American and European countries, mainly Russia, Canada and the United States of America. Oats are grown in temperate regions. They have a lower summer heat requirement and greater tolerance of rain than other cereals, such as wheat, rye, or barley, so are particularly important in areas with cool, wet summers, such as Northwest Europe and even Iceland. Oats are an annual harvest, and can be planted either in autumn (for late summer harvest) or in the spring (for early autumn harvest). [5]

It was used mostly for animal feeding and to some extent as human food. The use of oats as animal feed has declined steadily owing to emerging use and interest in oats as human health food. Oats consumption in human diet has been increased because of health benefits associated with dietary fibers such as beta-glucan, functional protein, lipid and starch components, and phytochemicals present in the oat grain. [6]

In the year 1997, USFDA approved the use of a health claim "3g/day of oat Beta- glucan may help lower blood total and low-density lipoprotein (LDL-C) cholesterol". [7] Over all consumption of oats has increased in the recent years due to its nutritional benefits; presence of Beta-glucan, antioxidants like Avenanthramides, vitamin E (tocotrienols and tocopherols). [8]


  Oats versus Other Grains Top


Compared with other cereals (wheat, rice, barley, buckwheat, and rice), oats contain higher content of protein, and the composition of oat amino acid is more reasonable [Table 1]. Moreover, the levels of crude fat, showing the nutritional and functional potential, in oats are much higher than that of other cereal grains, which leads oat to become an excellent source of functional food. Oat lipids are rich in polyunsaturated fatty acids, Vitamin E, and plan sterols. Judd and Truswell [9] concluded that both the lipophilic and lipophobic components of oat play a major role in decreasing serum cholesterol in humans. However, there is no information about the effect of these components other than beta-glucan in oat on the reduction of serum cholesterol in animals or humans. Moreover, oats are therapeutically active against diabetes, high blood pressure, inflammatory state, and dyslipidemia rather than other grains which are predominantly insoluble such as wheat or rice. This makes oats a unique cereal.
Table 1: Comparison of oats with other cereals


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In oats, there are more than 20 distinct forms of avenanthramides (AVEs) differing in the substituents of the acid rings, but the three major forms are A, B, and C. They help in reduction of coronary heart disease (CHD) as they posses anti-inflammatory and antiproliferative properties and also cause vasodilation, anti-itch and cytoprotection effects. A randomized placebo-controlled three-way crossover study was conducted to determine the bioavailability and bioactivity of AVE A, B, and C in healthy older adults with 1-week washout period. Six free-living patients were asked to consume 360 ml skim milk alone (placebo) or containing 0.5 or 1 g avenanthramide-enriched mixture (AEM) extracted from oats. Plasma samples were collected over a 10-h period. The bioavailability of avenanthramides (AV-A) was 4-fold larger than that of avenanthramides (AV-B) at 0.5 g AEM dose. Thus, oats AV are bio-available and increase antioxidant capacity in healthy older adults.

Another beneficial compound found in oats is tocols also known as Vitamin E. These are natural antioxidants in grains that may benefit human and animal health. It includes both tocopherols and tocotrienols. They help in scavenging of free radicals, thereby helping in lowering the cholesterol levels. Certain trace elements such as flavonoids, saponins, lignans, and sterols are found in oat grain, but in minor quantities. These compounds are bioactive and possess antioxidant properties.


  Value and Functionality Capture of Oats Top


Oats is a multifunctional grain. Its uses include animal feed, human food and raw material for food, health care, and cosmetic products. [Figure 1] shows the value pyramid and functionality of oats. The major components of oats that contribute to its functions include protein, oil, starch, and beta-glucan. [10]
Figure 1: Value pyramid

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  Nutrient Composition of Oats Top


Oats are unique among the cereals. It consists of a large amount of total proteins, carbohydrates, i.e., starch crude fat, dietary fiber (nonstarch), unique antioxidant, and vitamins and minerals [Table 2]. They also contain a varied range of phenolic compounds including ester-linked glycerol conjugates, ester-linked alkyl conjugates, ether- and ester-linked glycerides, anthranilic acids, and AVEs. These compounds possess high level of antioxidant activity. These antioxidants are concentrated in the outer layer of the kernel in the bran fraction of the oat grain. The nutritional benefits of oat have attracted attention from researchers worldwide and have resulted in the increased interest of food industry in using oats as food ingredient in various food products including infant food, oat milk, beverages, breakfast cereals, and biscuits. Whole grain oat contains considerable amount of valuable nutrients such as proteins, starch, unsaturated fatty acids, and dietary fiber as soluble and insoluble fractions. Oat also contains micronutrients such as Vitamin E, folates, zinc, iron, selenium, copper, manganese, carotenoids, betaine, choline, sulfur-containing amino acids, phytic acid, lignins, lignane, and alkyl resorcinols. Although wheat and rice are consumed in considerably higher quantities worldwide than oat, oat has the advantage that it is consumed as a whole grain cereal normally than its processed products. Increasing recognition is now being given to the consumption of whole grain cereals due to the pro-phylactic benefits they provide. [11]
Table 2: Composition of oats fiber and beta-glucan (g/kg dry weight)


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  Health Claim on Oats Top


The USFDA has allowed a health claim for an association between consumption of diet which is high in oat meal, oat bran, or oat flour, and reduced risk of CHD. This represents the first health claim for a specific food under the Nutrition Labeling and Education Act (1990) and follows on the long history of investigation and controversy. The claim is based on many clinical studies that concluded oat products may reduce serum cholesterol levels, a risk factor in CHD. Beta-glucan is accepted as a main active ingredient, but this does not imply that any source of beta-glucan is allowed; the health claim is especially for oat bran, rolled oats (oatmeal), and oat flour, and does not hold true for other sources of beta-glucan such as oats products or barley. [12]

The European Food Safety Authority (EFSA) approved the following health claim for food containing beta-glucan derived from oats or oat bran, or mixtures of nonprocessed or minimally processed beta-glucans: "Regular consumption of beta-glucans contributes to maintenance of normal blood cholesterol concentrations in the body of the consumer." Like that of FDA, EFSA has also concluded that an intake of 3 g beta-glucans per day was the minimum dose. The EFSA also stated that the intake could be distributed over one or more servings, without giving any lower limit for the beta-glucan content of food products.

Health claims regarding the association between cholesterol-lowering and soluble fiber from oat products/oat beta-glucan (OBG) have been approved by the food standards agencies worldwide (United States: US Food and Drug Administration; Canada: Health Canada; Europe: European Food Safety Authority; Australia and New Zealand: Food Standards Australia New Zealand; Malaysia: Ministry of Health Malaysia). [13],[14],[15],[16],[17]


  Processing of Oats Top


Oats are processed to make it palatable and also to improve nutrient availability as shown in [Figure 2]. Oat kernel is largely nondigestible and is thus milled to make it suitable for human consumption and absorption.
Figure 2: Processing of oats

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There are few steps followed while milling oats:

  1. Dehull - It helps to expose the groat
  2. Exposure to heat - The heat processing helps to inactivate the enzymes that cause rancidity and help in developing flavor
  3. Cut/flake/roll/grind - Oat groats are cut, rolled, ground, or flattened. These groats of varying sizes are used to make oat flakes/oat flour/oatmeal or as an ingredient in products such as cookies/bread/bars, etc.

  Glycemic Index of Various Forms of Oats Top


During processing of oats, this cereal undergoes change in physical characteristics which may influence serum glycemic response. According to a systemic review, the effect of different processes on acute postprandial glycemic response, quantified using glycemic index (GI) measurements. [Table 3] below shows variety of oats and its glycemic index (GI).
Table 3: Variety of Oats and GI values


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The data revealed that steel-cut and large-flake oats have low GI value whereas muesli and granola have medium but quick-cooking oats, and instant oatmeal (IO) fell in the category of high GI value.

The analysis establishes that differences in processing protocols and cooking practices modify the glycemic response to foods made with whole-grain oats. Smaller particle size and increased starch gelatinization appear to increase the glycemic response [13] (Tosh and Chu, 2015).

The effects of various commercial hydrothermal processes (steaming, autoclaving, and drum drying) on the levels of selected oat antioxidants were investigated. Steaming and flaking of dehulled oat groats resulted in moderate losses of tocotrienols, caffeic acid, and the AVE Bp (N-(4'- hydroxy)-(E)-cinnamoyl-5-hydroxy-anthranilic acid), while ferulic acid and vanillin increased. The tocopherols and the AVEs Bc (N-(3',4'- dihydroxy-(E)-cinnamoyl -5-hydroxy-anthranilic acid) and Bf (N-(4'- hydroxy-3'- methoxy)-(E)- cinnamoyl-5-hydroxy-anthranilic acid) were not affected by steaming. Autoclaving of grains (including the hulls) caused increased levels of all tocopherols and tocotrienols which were analyzed except beta-tocotrienol, which was not affected. Vanillin, ferulic, and p-coumaric acids also increased, whereas the AVEs decreased, and caffeic acid was almost completely eliminated. Drum drying of steamed rolled oats resulted in an almost complete loss of tocopherols and tocotrienols, as well as a large decrease in total cinnamic acids and avenanthramides. The same process applied to whole meal made from groats from autoclaved grains resulted in less pronounced losses, especially for the avenanthramides which were not significantly affected. [18]


  Effect of Cooking on Oats Top


The effects of cooking, baking, and drying on the extractability of OBG were comprehensively evaluated by Johansson et al. Cooking was found to release more soluble beta-glucan whereas baking decreased the amount of soluble beta-glucan probably due to enzyme activity in the flour toward beta-glucan. Drying (overnight at 60°C) decreased the amount of soluble beta-glucan both in bread and fermentate, but not in porridge. All processing conditions did not influence the ratio of cellotriosyl to cellotetraosyl residues in soluble beta-glucan molecular structure. [19] Major viscosity losses in oat gum have been observed during centrifuging, which produce high shear damage to beta-glucan residues (Wood et al. 1989). Extrusion processing at high temperature might decrease the molecular weight of beta-glucan. [20] The cholesterol-lowering effect of OBG depends on its viscosity in the small intestine and therefore its molecular weight. A high molecular weight means it can be released from the food matrix during digestion and form a viscous gel inside the small intestine.


  Cholesterol Reduction with Oats Top


According to scientific research results it has been known to scientists for over 2 decades that ß-glucan (oat ß-glucan) has strong cholesterol and triglyceride lowering properties leading to reduced cardiovascular diseases. [21]

By the early 1960s, Groot et al. had observed the cholesterol-lowering effects of rolled oats in humans. Since then, many human studies have confirmed this health benefit. From the meta-analysis of 20 trials, incorporating oat products into the diet was found to cause a modest reduction in blood cholesterol levels, and large reductions were observed in hypercholesterolemic subjects, particularly when a dose of 3 g or more of soluble oat fiber was employed. [22]

Behall et al. (1997) reported that 2.1 g of ß-glucan per day reduced total cholesterol levels by 9.5%. [23] The studies of Anderson and colleagues first brought the potential cholesterol lowering effect of oats to public attention, showing that oat bran reduced total serum cholesterol in hypercholesterolemic subjects by as much as 23%with no change in high density lipoprotein (HDL) cholesterol.

A recent meta-analysis, which included 25 studies on oat products, found that 3 g of soluble fiber from oats (three servings of oatmeal, 28 g each) reduced total cholesterol and low-density lipid by approximately 0.13 mmol/L (i.e., 2%).

A meta-analysis of 67 controlled trials of dietary soluble fiber as a single intervention showed that the effects on total cholesterol and LDL cholesterol levels were modest. For example, the addition of three 28 g servings of oats per day decreases LDL cholesterol levels by 5 mg/dL (0.13 mmol/L).

A systematic review of literature was extracted from Embase, Medline, and the Cochrane Library, which identified 654 potential articles. Seventy-six articles describing 69 studies met the inclusion criteria. Most studies lacked statistical power to detect a significant effect of oats on any of the risk factors considered: 59% of the studies had less than thirty subjects in the oat intervention group. Out of 64 studies that assessed systemic lipid markers, 37 (58%) and 34 (49%) showed a significant reduction in total cholesterol (2-19% reduction) and LDL cholesterol (4-23% reduction), respectively, mostly in hypercholesterolemic subjects. Few studies (three and five, respectively) described significant effects on HDL cholesterol and TAG concentrations. Long-term dietary intake of oats or oat bran has a beneficial effect on blood cholesterol.

A meta-analysis published in the American Journal of Clinical Nutrition shows that daily consumption of at least 3 g OBG reduces cholesterol levels. This effect was observed in lean, overweight, and obese male and female adults, with and without type-2 diabetes, across 28 randomized controlled trials.

The cholesterol-lowering effect of oat products has been attributed specifically to OBGs. In a subsequent study, oat gum containing 80% of beta-glucans significantly reduced the total and LDL cholesterol levels of hypercholesterolemic human subjects without effects on plasma HDL cholesterol, suggesting that beta-glucan could be the major component of oats responsible for the overall cholesterol-lowering effect. [24]

A systematic review of observational studies also supported the fact that increased oats consumption has a beneficial effect on serum cholesterol concentration, particularly in hypercholesterolemic subjects. This is consistent with a rigorous meta-analysis by Ripsin et al. (90) which concluded that about 3 g/day of soluble fiber from oat products can lower total cholesterol by 0·13-0·16 mmol/L, with a greater reduction in individuals with higher initial cholesterol concentrations. A 1% reduction in total cholesterol or LDL cholesterol is associated with a 2-3% or 1% decreased risk, respectively, of CHD. The magnitude of the effect found in the present review (3-6% for total cholesterol and 4-8% for LDL-cholesterol when considering studies with a sufficient sample size) would translate to a 6-18% decrease in CHD risk, which would equate to a substantial health benefit at a population level.

The soluble fiber in oats helps lower total and LDL cholesterol, but scientists now say that the cardiovascular health benefits of oats go beyond fiber.

Eleven top scientists from around the globe presented the latest findings on the powerful compounds found in oats in a scientific session in Dallas, TX. Scientists described research on the diverse health benefits of oats and emphasized the growing evidence that the type of phenolic compound AVE-found only in oats-may possess antioxidant, anti-inflammatory, anti-itch, and anti-cancer properties. The culmination of the studies suggests that oat AVEs may play an important role in protecting the heart.

Mechanism of cholesterol reduction

A study on 4-week-old Wistar rats was conducted to understand the mechanism of cholesterol reduction with oats consumption. Rats were divided into six groups of 7 rats each with similar mean body weights and serum cholesterol concentrations. Rats were fed with the experimental diets containing 10% oats flour for 30 days. The results indicated that dietary oat improved hypercholesterolemia by increasing the excretions of fecal bile acids, and this improvement was not only related to beta-glucan, but also attributed to the lipids and proteins. Oat proteins decreased serum total cholesterol and LDL cholesterol contents due to their low lysine/arginin and methionine/glycine ratio. The co-existence of oleic acid, linoleic, Vitamin E, or plant sterols accounted for the hypocholesterolemic properties of oat lipids.

The mechanism by which oat-soluble fiber lowers blood lipids is probably related to its ability to either reduce the absorption of cholesterol and bile acids or delay lipid digestion, although two recent studies suggest that oats may also reduce LDL oxidation due to the presence of various phenolic compounds. In addition, oatmeal has been shown to prevent the constriction of arteries, an early sign of heart disease, when served with a high-fat meal. Beta-glucans decrease the absorption and re-absorption of cholesterol, bile acids, and their metabolites by increasing the viscosity of the gastrointestinal tract contents. [25]

The mechanism for beta-glucans to lower LDL is considered to be mediated by bile acids binding property of beta-glucans. Therefore, beta-glucans increase the exclusion of bile acids, and this, in turn, activates cholesterol 7 alpha-hydroxylase and upregulates low-density lipoprotein receptor, and thus increase the transport of LDL into hepatocytes and the conversion of cholesterol into bile acids as seen in [Figure 3].
Figure 3: Action of oats against dyslipidemia

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Other soluble dietary fibres that are resistant to digestion by human enzymes such as pectins, guar gums, psyllium can also have similar effects. [26],[27] The advantages for beta-glucans are that they exhibit high viscosities at very low concentration (1%) and are stable with pH. The viscosity determined by water solubility and molecular weight has been shown to affect the hypocholesterolemic effect of beta-glucans. [28] Thus, different structure of beta-glucans may have different properties to cause viscosity. Some betaglucans may have no effects. It is important to characterize what sort of structure features are essential for lowering lipids and antidiabetic effects. [29]


  Oats and Prebiotic Effect Top


Beta-glucan present in oats has been shown to stimulate the growth of bifido bacterium and lactobacillus in a dose-dependent manner and also inhibit Enterobacillus growth in the colon in a study conducted on mice. [30] The contents of short-chain fatty acids in the colon were significantly higher in mice fed with OBG compared to those fed with the controlled diet. Shen et al. (2006). [30] indicated that prebiotic effects of OBG were associated with their molecular weight. Another study conducted on rats where rats were fed with oat bran diets and results showed that there was an increase in the content of lactobacilli and bifido bacteria in fecal flora as compared with other group which was fed fiber-free diets. [31]

Kedia et al. [32] compared the fermentation ability of oat fractions (pearling, whole flour, and bran) by human Lactobacillus strains in vitro. Oat fractions with a high concentration of soluble fiber have resulted in greater growth of Lactobacillus reuteri, Lactobacillus plantarum, and Lactobacillus acidophilus. The 1-3% of pearling oat sample containing the highest amount of soluble fiber and beta-glucan had the greatest fermentation ability, and the nondigestible components of this fraction treated with an in vitro digestion model also showed the greatest growth of the three lacto bacillus strains.

Mechanism of oats as a prebiotic

Oligosaccharides produced from beta-glucan have been demonstrated to act as selective factors, favoring growth of at least some known probiotic bacterial strains. The favorable effect on colon function is based partly on the enhanced production of microbial mass with good water retention properties, partly by the bulking effect of the insoluble components of the fiber. Soluble dietary fiber has been found to increase the fermentation activity in the large intestinal bowel because of the production of butyric acid, also accelerates the growth and colonization of some strains of probiotic bacteria, has been found to increase the production of microbial mass and thereby aids the removal of nitrogen via stool. Increases the wet weight of feces, thus decreases the constipation problems. Short-chain fatty acids formed used as energy source for colonic mucosa as shown in [Figure 4]. Effect of beta-glucans in increasing caecal and colon mass, by increasing the resistance of starch to digestion, and hence altering the amount of fermentable material reaching the caecum.
Figure 4: Mechanism of oats as prebiotic effect

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  Oats and Diabetes Top


OBG plays a role in modulating the metabolic effects observed after fiber-rich meals. As a soluble fiber with viscous characteristics, it affects gastric emptying, gut motility, and nutrient absorption, which are reflected in lower postprandial glycemic and insulin responses.

The benefits of oats have been officially endorsed by the American Dietetic Association (ADA). According to a 1996 report from the ADA, oat consumption does improve glucose control by moderating the large blood glucose spikes that cause metabolic upsets among diabetics.

Blood sugar control can be determined by the cooking time of a cereal, in this case the longer cooking time (of oats) more thorough is the breakdown of cell wall, therefore, the rate at which beta- glucans enters the blood stream is faster; once it enters the blood stream, it stimulates insulin production. Low glycemic index of oats may help in regulating blood sugar levels. The quantity of oats and cooking time work together to deliver the best possible glycemic control.

A study revealed the efficacy of beta-glucans from oats which helped in slowing down the blood sugar levels. According to this study, dietary oats were compared with mixed-food diets containing other water-soluble fibers. The results showed that the mixed food diet did not match the effectiveness of daily servings of ordinary whole oats in controlling postmeal blood sugar.

A beta-glucan-rich diet was tested against the American Diabetic Association's recommended diet for type-2 diabetics. About 16 males with well-controlled type-2 diabetes were split into two groups of 8, one assigned to continue with the ADA's diet, the other fed a modified low-calorie diet featuring OBG sweetened by sucrose and fructose. Both groups maintained their diets for 4 weeks while exercising 60 min each day. Glucose, along with body mass index (BMI) and other measures was monitored. Both diets reduced participant's weight, BMI, lipid profile, and basal glucose. The significant difference was that the beta-glucan-rich diet outstripped the ADA diet in controlling metabolic and other nonweight body changes, the most reason is that oats should figure importantly in the diet of every person suffering type-2 diabetes.

Another study investigated the postprandial effect of 2 oat products, namely flaked oats (muesli) and boiled oat flakes (oat porridge), in healthy subjects. Both products had a similar GI effect as white bread, while intake of boiled oat kernels tested at the same time gave lower glucose and insulin responses. Tappy et al. (1996) [33] gave diabetic subjects a cooked extruded oat bran concentrate for breakfast at different doses (4.0, 6.0, and 8.4 g beta-glucan). The maximum increases in plasma glucose for the oat bran meals were 67%, 42%, and 38%, respectively, compared with a continental breakfast (35 g available carbohydrates). Other studies also showed, that when a more concentrated oat extract is consumed in cooked, boiled, or baked form, it lowers the glucose and insulin responses. [34]

Tapola et al. (2005) [35] in their study, "glycemic responses of oat bran products in type-2 diabetic patients" also concluded the same when they studied volunteers with type-2 diabetes fed on oat bran flour, oat bran crisp, and a glucose load providing 12.5 g glycemic carbohydrate (series 1) and 25 g glucose load alone, and 25 g glucose load with 30 g oat bran flour (series 2). In both series, oat bran products rapidly lowered postprandial glucose concentrations than after the 12.5 g or 25 g glucose load during the 1 st h, but the glucose concentration was greater at 120 min after the oat bran products ingestion than after the glucose load. This decrease of glucose absorption will decrease insulin release and thereby attenuate pancreatic insulin response. Therefore, OBG has a greater effect at lowering peak glucose absorption concurrently with an attenuated insulin response, which has a high significance in control and prevention of type-2 diabetes. [21],[36]

Mechanism of oats in diabetes

The potential reduction of glycemic response following ingestion of dietary fiber has led to proposals which implicate that the amount and quality of fiber increased the intrinsic viscosity of the food in combination with fluids and hence the gastrointestinal environment; maintenance of physical integrity of the food material and incomplete starch gelatinization. Beta-glucans delay gastric emptying, gut motility, and the intestinal absorption of nutrients such as digestible carbohydrates [Figure 5]. Higher levels of fermentable material in the caecum will lead to increased short-chain fatty acid levels in the caecal contents. This "bulking" effect of dietary fiber may be a consequence of increased water holding capacity of fiber-rich foods, and thus reducing postprandial hyperglycemia and insulin secretion. This provides health benefits for those with type-2 diabetes, and is also associated with reduced risk of developing the disease and insulin insensitivity. Other notable, but less well-documented effects of beta-glucans include the diminished absorption of nutrients, prolonged postprandial satiety, and increased stool bulk and relief of constipation.
Figure 5: Mechanism of action of oats against diabetes

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  Obesity and Blood Pressure Top


Weight loss is often advocated as a first-line treatment for hypertension and hypercholesterolemia, and the identification of weight-loss diets likely to maximize the effects on blood pressure and blood lipids is of considerable importance. In a study, a hypocaloric diet-containing oats were given for over 6 weeks. It resulted in greater decreases in SBP, total cholesterol, and LDL cholesterol than did in a similar diet without oats. In this normotensive population, a hypocaloric diet-containing oats were associated with a decrease in SBP of 6 mm Hg and a net advantage over the control diet of 25 mmHg. Many studies have shown beta-glucans reduced body weight. [37],[38] For example, Sanchez and Colleagues et al. (2008) showed the lowering of body weight effect of oat bran beta-glucan at the concentration of 10%. [39]

According to Anderson (1990) and Malkki, and Virtanen (2001) [26],[40] the diet which is rich in soluble fiber can affect fullness (satiety) and promote weight loss for a number of reasons including a slower rate of meal intake, a delay in gastric emptying, elevation of cholecystokinin (a gut hormone correlated with prolonged satiety), and production of gas and short-chain fatty acids by fermentation of the fiber in the colon. A study was conducted to examine the effect of two types of oatmeal and an oat-based ready to eat breakfast cereal (RTEC) on appetite and assessed differences in meal viscosity and beta-glucan characteristics among the cereals. About 48 subjects were enrolled in a randomized crossover trial. Subjects consumed isocaloric breakfast meals containing instant oatmeal (IO), old fashioned oatmeal (SO) or RTEC in random order at least a week apart. Starch digestion kinetics, meal viscosities, and beta-glucan characteristics for each meal were determined. IO and SO had higher beta-glucan content, molecular weight, gastric viscosity, and larger hydration spheres than the RTEC, and IO had greater viscosity after oral and initial gastric digestion (initial viscosity) than the RTEC. IO and SO improved appetite control over four hours compared to RTEC.

Oat compounds provide various opportunities for incorporating oats in functional food products. There is a great need to determine the bioavailability of antioxidants from oat and other food sources and to determine various effects on human and animal health. Oats contain very interesting components including antioxidants and beta-glucan. Oat, being a convenience food material consumed by humans irrespective of the age, requires more scientific attention to justify and modify its nutraceutical status in geriatric as well as pediatric diets. Research and development are further needed to determine novel functional compounds in oat to extract these components in fractions that can be incorporated in food products.

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Conflicts of interest

There are no conflicts of interest.

 
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    Figures

  [Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5]
 
 
    Tables

  [Table 1], [Table 2], [Table 3]


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Oats versus Othe...
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