|Year : 2014 | Volume
| Issue : 1 | Page : 39-42
Whole grains: Beyond fiber (Dr. Vandana Bambawale Oration at AIAAROCON-Pune on 9th February, 2013)
Shashank R Joshi
Lilavati and Bhatai Hospital, Mumbai, Maharashtra, India
|Date of Submission||15-Oct-2013|
|Date of Acceptance||31-Oct-2013|
|Date of Web Publication||30-Dec-2013|
Shashank R Joshi
Joshi Clinic, 12 Golden Palace, Turner Road, Bandra West, Mumbai 400 050, Maharashtra
Source of Support: None, Conflict of Interest: None
|How to cite this article:|
Joshi SR. Whole grains: Beyond fiber (Dr. Vandana Bambawale Oration at AIAAROCON-Pune on 9th February, 2013). J Obes Metab Res 2014;1:39-42
| Introduction|| |
There are four major classes of biomolecules - carbohydrates, proteins, nucleotides and lipids. Carbohydrates, or saccharides - which form a significant part of our diet as a major food source, are the most abundant of the four and have several roles in living organisms, including energy transportation, as well as being structural components of plants and arthropods. Carbohydrate derivatives are actively involved in fertilization, immune system, development of disease, blood clotting and development.
Carbohydrates are called so because the carbon, oxygen and hydrogen they contain are generally in proportion to form water with the general formula Cn (H 2 O) n. When multiple monosaccharides make a chain they form polymers. Carbohydrates can function as long-term food storage molecules, as protective membranes for organisms and cells and as main structural support for plants and constituents of many cells and their contents.
The National Institute of Nutrition - India (NIN), recommends a diet consisting of 60-70% carbohydrates.  Majority of these carbohydrates are consumed in the form of cereals, of which rice and wheat form the major source. 
All grains start life as whole grains. In their natural state growing in the fields, whole grains are the entire seed of a plant.  This seed (which is called a kernel) is made up of three key edible parts - the bran, the germ and the endosperm - that are protected by an inedible husk, which protects the kernel from assaults by sunlight, pests, water and disease. The bran is the major contributor of fibre and other phytochemicals in a grain. The germ is rich in vitamins, minerals and unsaturated oils, but forms a minute fraction of the wholegrain. The interior contains mostly the starchy endosperm, which is made of 50-75% starch; the endosperm also contains storage proteins and cell wall polymers. Comparatively, few vitamins, minerals and phytochemicals are located in this part of the grain, which provides stored energy for the germ - the seed's reproductive kernel that nestles inside the endosperm.
The advent of industrialised roller mills in the late 19 th century marked the entry of refined grains in our diet. Even though, refining makes the grain easier to chew, easier to digest and easier to store, there is a nutritional price to be paid for refined grains.
A growing body of research shows that returning to whole grains and other less-processed sources of carbohydrates and cutting back on refined grains improves health in myriad ways. These conclusions are supported by the effects of increased consumption of refined cereal products being associated with an increased risk of digestive disorders and various cancers.  However, this evidence is not sufficient to establish the relationship between high wholegrain consumption and reduced development of chronic diseases. These diseases are associated with our lifestyles and unbalanced dietary habits such as diets lacking in fibre. In recent times, the belief that it is not only fibre but the synergistic action of fibre and other bioactive compounds present in the grain that provides protective benefits is strengthening. Few physiological mechanisms are established, however, the precise mechanisms involved are far from being elucidated. 
This review is an attempt to summarise the possible physiological mechanisms involved.
| Whole Grains and Diet|| |
Grain-based foods contributes maximum to the Indian diet. In addition to fibre, whole grains contain vitamins and minerals along with other phenolic compounds and bioactive phytochemicals that synergistically reduce the risk of chronic diseases. Over the past few decades various governmental, scientific and non-profit organisations have recommended whole grains as part of a healthful diet. 
While the standards for whole grain are different in each market. India has not acknowledged whole grain definitions as yet. Definitions have been proposed by various regulatory/legal bodies in few countries. The definition by the US Food and Drug Administration (FDA), 1999 for whole grain foods states "For purposes of bearing the prospective claim, the notification defined 'whole grains' as foods that contain 51% of total weight or more whole grain ingredient(s) by weight". This definition was debated upon by the European Whole Grain Task force in 2008 and stated that "Using total weight gives advantage to products sold by dry weight such as crackers and ready-to-eat cereal. Because foods like breads have a proportionally high water content, even some breads made with all whole grain flours, but containing significant amounts of nuts, seeds and fruit would fail to meet the 51% by weight rule".  Till date, even though there is no international consensus for a whole grain product, each country maintains its own set of definitions and standards.
In 2005, US Dietary Guidelines advised an increase in consumption of whole grains - "three or more ounce equivalents", each day as part of a healthy diet.  In 2007, Canada's Food Guide also underwent a revision and recommended that at least half of the grain products consumed in a day should be whole grain.  In Australia as well, Go Grains - in collaboration with the International Life Sciences Institute, convened an expert panel to establish an Australian daily target for wholegrain intake. After reviewing the scientific evidence, the expert panel agreed that 48 g of whole grains each day is an achievable, evidence-based Daily Target Intake for adults, teens and older children.  Grain Foods also form the base of the Food Guide Pyramid, which recommends consuming 6-11 whole grain servings per day.  Even in the recently devised Dietary Guidelines for Indians developed by the NIN cereal-based foods form the base of the food pyramid.  The incorporation of whole grains as part of healthy diets by various institutions showcases the acceptability of the goodness of whole grains.
| Whole Grains and Fibre|| |
Majority of the health benefits of whole grains is attributed to the fibre content and the physiological mechanisms of fibre in managing satiety, fecal bulking, digestive viscosity, short-chain fatty acids (SCFA) production and/or reduced glycaemic response.
Fibers, especially the soluble ones, increase the viscosity of the alimentary bolus and hence lengthen the gastric-emptying and intestinal-transit times. In addition, the rate of starch digestion by pancreatic amylases is delayed by soluble fibers in vitro - an effect, which is related to the viscosity of the fibres which may delay the interaction of the enzyme with its substrate. This mechanism limits the postprandial rise in plasma glucose concentration by reducing the rate of carbohydrate absorption from the gastrointestinal tract. 
Of all the dietary fibres, the cholesterol-reducing property of β-glucan (a form of soluble fiber) from oats is most extensively studied. β-glucan in oats encapsulates bile acid as mixed micelles and aids their excretion. This increase in drainage of bile acid from liver can induce a reduction in serum cholesterol.  Evidence suggests that some of the soluble fibres bind to bile acids or cholesterol during the intraluminal formation of micelles. The resulting reduction in the cholesterol content in liver cells leads to an up-regulation of low-density lipoprotein (LDL) receptors, which in turn increase clearance of LDL-cholesterol.
Other beneficial effects of fibre include: inhibition of hepatic fatty acid synthesis by products of fermentation (production of short-chain fatty acids such as acetate, butyrate and propionate), changes in intestinal motility, fibers with high viscosity cause reduced absorption of macronutrients leading to improved insulin sensitivity, increased satiety and long lasting inhibition of hunger. 
Dietary fibres also help manage obesity because they are known to increase satiety and hence manage caloric intake. They are thought to impact on satiation (the satisfaction of appetite during feeding that marks the end of eating and satiety (inhibition of hunger as a result of having eaten), because of their properties of adding bulk (satiation) and producing viscosity (satiety).
Pre-abosrptive factors such as gastric distention, effort and time required for chewing are important for improving satiation. For this reason, the bulking and textural properties of fibre make it an attractive ingredient for enhancing satiation. Adding bulk to the diet with fibre will also reduce the energy density of the diet. Satiety signals are generated both pre- and post-absorption. Viscous soluble fibres may be useful because they prolong the intestinal phase of nutrient digestion and absorption. This means that there is a longer time over which macronutrients can interact with the pre-absorptive mechanisms of satiation and satiety, as well as prolong the time course of post-absorptive signals. 
However, many of the scientific studies and meta-analyses have shown that products made of whole grain are associated with lower prevalence of non-communicable diseases and this benefit is attributed to the whole grain and not to fibre alone. Hence, it is now being recognised that not only fibre but other bioactive compounds present in whole grains act synergistically to provide the required health benefits.
| Whole Grains and Nutrients|| |
Physiological mechanisms behind this protection are complex since grain cereals are a package of bioactive compounds - each one having its own positive physiological effects.  Even though a lot remains unraveled - especially the synergism of these various mechanisms, the few recognised mechanisms of these nutrients are highlighted.
Omega-3 fatty acids, i.e. alpha-linolenic acids, are known for their positive effects on blood clotting, thrombosis and inflammation.  It is known to have anti-atherosclerotic effect via inhibition of oxidative-stress-mediated CD40L - a protein known for its pro-thrombotic properties and suppresses levels of arachidonic acid and eicosanoids in tissue. , Certain sulfur compounds are known for their antioxidant property. In whole grains, the most prevalent sulfur compounds are reduced glutathione (glutathione sulfhydryl; GSH), methionine and cysteine, of which, methionine is supplied predominantly in a cereal-based diet.  Methionine - a precursor of S-adenosylmethionine, is a universal methyl donor  that may possess some antioxidant activity.  GSH, on the other hand, is a strong antioxidant known to detoxify certain toxic electrolyte metabolites of xenobiotics and of reactive oxygen intermediates generated intracellularly and at sites of inflammation. , Cysteine is an antioxidant and also a constituent of metallothionein - another potent antioxidant. 
There are other types of indigestible carbohydrates such as resistant starches (RS), lignans and some oligosaccharides known to have certain positive physiological effects. RS are known to decrease glycemia, promote lipid oxidation and have some prebiotic effects. RS have been shown to increase fat oxidation in humans - probably by an increase in SCFA production that inhibits glycolysis in the liver, making the body more dependent on fat-derived sourced as fuel - this effect has been associated with a concomitant decrease in carbohydrate oxidation and fat storage. ,, Oligosaccharides are known to decrease glycaemia and have cholesterol-lowering effects because of its link with SCFA production in the colon.  Lignins, on the other hand, exhibit antioxidant property due to the presence of phenolic hydroxyl groups. It reduces bile acid absorption by acting as bile salt sequestrating agent. Besides it also reduces fat absorption and increases cholesterol turnover. ,,,
In addition, there are various vitamins and minerals present in cereals known for their positive functions and other polyphenols known for their antioxidant properties. Along with this there are certain specific compounds present in cereals such as gamma-oryzanol in rice and avenanthramides in oats that provide additional nutritional and health benefits.  Since all of these components in whole grains work synergistically to provide the overall protective benefits, their synergistic mechanisms are yet to be elucidated. Nutrigenomics could possibly be looked upon to study complex physiological effects of the whole grain "package". Interventional studies are therefore needed to move a step forward in the understanding of the mechanisms involved in whole grain cereal protection. 
| Whole Grain Challenges|| |
Since whole grains are known to have so many beneficial effects, it seems prudent to increase wholegrain consumption on a regular basis. To help consumers increase their whole grain intake, it is important for manufacturers to optimise flavour, colour and texture of foods made with whole grain ingredients to improve palatability. It is also important that the formulation and processing of foods made with whole grains is different and sometimes develop technologies that can be more challenging compared to refined grain foods. To increase palatability of whole grain foods the easiest options that the food industry opts is to add sugar and sodium in the foods; hence, another challenge that the industry faces is to develop products with lower sodium and sugar content.
To help increase whole grain intake, it is important to customise the inclusion level and type of whole grain ingredients used in different grain-based foods and food components. For this purpose, having certain guidelines on the prescribed levels of whole grain would be of great help. Other strategies would be to develop new types of foods, as well as to popularise less-familiar grains and in Indian context revisit grains used in traditional cuisines.
Controlling grain-growing conditions, such as the use of appropriate fertilisers, may improve the mineral profile of the grains, as well, using certain plant-breeding techniques may lead to production of nutritionally superior grains. Besides growing conditions applying specifically designed technologically advanced processes may also help in improving the nutritional quality of whole grains.
| Conclusion|| |
Whole grains provide protective benefits not just because of their fibre content, but because of the synergy between various macro- and micronutrients they contain.
While there are recommendations of daily intake of whole grain in various countries, India is yet to consolidate recommendations for an Indian diet. Therefore, there is a need to develop specific Indian recommendations for the intake of whole grains. It is essential for the government, health organisations, medical fraternity and institutions to form an expert panel and identify ideal whole grain intake based on available scientific evidence.
In the current scenario where there is no definite Indian Guidelines/recommendations on the whole grain intake, credible existing guidelines should be considered. As pointed out it the article, the US FDA guidelines should be considered since they are globally recognised and are of a good repute. They state that 51 % of the total cereal intake should comprise of whole grains. Products abiding to this simple yardstick should be included in the daily diet.
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| Authors|| |
Shashank R. Joshi