Beta-Glucan-Rich Barley Helps Control Sugar

Barley Is the Best Source of Fiber Beta-Glucan-Rich Barley Helps Control Blood Sugar The viscous, soluble fiber reduces glucose and insulin levels as well as cholesterol levels By Will Block magine that you and your elephant, George, are on safari in the Kalahari Desert, and you get hopelessly lost. There’s no one around to help you—not even a Bushman. You have water with you, but no food, and the only vegetation far and wide is some scrubby trees. Days go by, and you’re starving—your body desperately needs more of its chief source of chemical energy, glucose. © iStockphoto.com/Cay-Uwe Kulzer You watch enviously as George calmly nourishes himself by eating the trees. You know they consist mainly of cellulose, a complex carbohydrate, and cellulose molecules consist entirely of . . . glucose! The glucose molecules are linked end-to-end to form the long cellulose polymers, which bond together to form tough fibers. The rest of the wood consists mainly of hemicelluloses (complex carbohydrates that contain glucose as well as other sugars) and lignins (complex polyphenols), both of which also help make wood hard and strong. So much glucose—so near, and yet so far. You know you can’t digest cellulose to get the glucose, as George can, and even if you could, you couldn’t eat the wood—it’s too tough, and you forgot to bring your Swiss army knife with its built-in wood shredder. You’d have to dissolve the wood in water to be able to get it down. But cellulose is, of course, insoluble as well as indigestible (to humans). Just as you start fantasizing about elephant meat (No! Not George!), a bush pilot spots you, and you’re saved. Whew! Insoluble Fiber Is Beneficial . . . So what did we learn from that story? That most dietary fiber consists of glucose in polymeric form, but it has no nutritional value because we can’t digest it. Also, whether or not something is water-soluble can make a heck of a difference. It certainly makes a difference inside you, where dietary fibers have traditionally been classified as either insoluble or soluble (both kinds of fiber are found in virtually all plant sources, although their compositions and proportions vary widely). The insoluble fiber, mainly cellulose, provides roughage, which softens and bulks up your stools and speeds them on their way through your colon. That’s beneficial, because the faster that stuff moves along, the less chance there is of your becoming constipated or developing diverticulosis (small outpouchings in the colon wall, where stagnant fecal matter can get trapped, causing the painful inflammation called diverticulitis). © iStockphoto.com/Vika Valter It was formerly thought that the roughage-induced fast-forwarding of feces would help prevent colorectal cancer by minimizing the chances of bacterial activity and chemical reactions that could produce potentially carcinogenic toxins. A number of significant recent studies, however, have failed to substantiate this belief—but the question is not settled. It is generally accepted, though, that fiber’s promotion of frequent elimination (which is more important than simple regularity) is a good thing. . . . But Soluble Fiber Is Even More Beneficial For insoluble fiber, that’s about it—there appear to be no other significant health benefits. That leaves soluble fiber, which has two major health benefits beyond the fast- forwarding effect: it reduces serum cholesterol levels, which helps prevent cardiovascular disease (CVD), and it reduces postprandial (after-meal) serum glucose levels and, therefore, serum insulin levels, which helps prevent type 2 diabetes. There is even a feedback of sorts between these two effects, because diabetes is a major risk factor for CVD (as well as other serious diseases), so preventing the former helps prevent the latter. Soluble fiber also reduces blood pressure, another way to help prevent CVD. Soluble fiber may have yet a third benefit, and it’s an important one: weight control. Although the results of scientific studies in this domain are mixed, there is evidence that a diet high in fiber (particularly from whole grains) can prevent weight gain or promote weight loss.1 This is especially true if the food source has low values of the glycemic index (a measure of the rate at which glucose from the digestion of carbohydrates enters your bloodstream) and the glycemic load (the more important measure of the overall glucose burden imposed on your bloodstream from a given meal). Barley Is Rich in Soluble Beta-Glucan One food—barley—stands out not only for being high in fiber (and in B-vitamins and various minerals, especially chromium) but also for having an extremely low average glycemic index (25), and a relatively low average glycemic load (11) to boot. Barley is rich in a viscous, soluble fiber called beta-glucan, which lowers serum cholesterol, glucose, and insulin levels and may contribute to weight loss.2 (Bear in mind that glucose and insulin levels always increase after a meal, and the reduction we’re talking about is a reduction in the amount of that increase.) One recently developed barley cultivar turned out, unexpectedly, to have about twice as much beta-glucan as normal barleys and about three times as much as oats (the only other significant source of beta-glucan).* That cultivar is called Prowashonupana, and among cereal grains, it has become a health superstar. (For more on beta-glucan and Prowashonupana, see the two sidebars; and for background information on all the topics being discussed here, see “Lowering Cholesterol with Beta-Glucan-Rich Barley” in the July 2007 issue.) *A cultivar is a race or variety of a plant that has been created or selected intentionally and maintained through cultivation, like grape varietals. Different cultivars can have widely differing characteristics. What Is Beta-Glucan, Anyway? Although not usually considered a gum, beta-glucan is closely related to gums, which are viscous, sticky, water-soluble, complex carbohydrates exuded by certain types of plants and algae. Many are used in the food, pharmaceutical, cosmetics, and other industries. Some natural gums you may have heard of are gum arabic, guar gum, and xanthan gum. In the food industry, gums are used as thickening and gelling agents, emulsifiers, and stabilizers. Like starch and cellulose, gums are polysaccharides, or complex carbohydrates, which are polymers of monosaccharides—simple sugars, such as glucose, fructose, galactose, xylose, arabinose, and mannose. The endless variety of polysaccharides comes not only from the variety of sugars (and their derivatives, such as glucosamine) that can form polymeric chains, but also from the different ways in which individual sugar molecules can be linked to each other to form those chains. A tiny portion of an immensely large beta-glucan polymer, which may contain up to about 1,000,000 glucose monomers. The properties of polysaccharides, including their solubility and their digestibility, thus depend not only on their molecular composition but also on the exact type of chemical linkages between the individual sugar molecules. Chemists use a system of Greek letters and Arabic numerals to designate certain aspects of these linkages. Greek letters, eh? As in β-glucans (beta-glucans)?* Yes, but there are also α-glucans (alpha-glucans). The distinction between the alpha and beta types of polysaccharides is extremely important. Starch, for example, is an insoluble polysaccharide consisting entirely of glucose molecules linked in the alpha configuration (an alpha-glucan)—and because it’s alpha, it’s digestible. The starch in plants is the principal source of glucose for our biochemical energy needs: when we digest starchy foods (“carbs”), the starch molecules are broken down to yield a great deal of glucose. *As with most types of biological polymers, there are many beta-glucans; the particular group of beta-glucans we’re interested in here is usually referred to in the singular, for simplicity. Cellulose, the principal constituent of plants’ cell walls, is identical to starch in being composed entirely of glucose monomers. But there’s one critical difference: the glucose molecules are linked in the beta configuration, which makes cellulose indigestible to humans (but not to many animals, which have the appropriate enzymes for the job). Technically, cellulose is a beta-glucan, but it’s not called that, to avoid confusion with the class of compounds that we do call beta-glucan(s). The confusion is eliminated if we use those Arabic numerals we mentioned, but the details of that system are too technical to discuss here. When Mother Nature modifies the structure of cellulose slightly (the numerals tell the tale), we get what is commonly called beta-glucan. Like cellulose, beta-glucan forms itself into long fibers, but unlike cellulose fibers, these ones are soluble, and they produce a very viscous, gel-like solution in our intestines. The way to achieve that is to eat barley or oats, the only two major sources of beta-glucan. Here’s another important point: whereas cellulose is totally indigestible, beta-glucan is somewhat digestible—not in the small intestine, however, where most digestive processes occur, but in the large intestine. There it gets fermented to short-chain fatty acids, which can be absorbed into the bloodstream, and it’s believed that these acids may inhibit cholesterol synthesis in the liver. Unlike cellulose, therefore, beta-glucan has both nutritional and medicinal value. Cellulose, by the way, was discovered in 1834 by the French chemist Anselme Payen. By calling it cellulose (because it existed in cell walls), he set the fashion for using the “ose” suffix in the naming of carbohydrates. One year earlier, he had set the fashion for using the “ase” suffix in the naming of enzymes, when he discovered and named diastase, the first enzyme to be prepared in concentrated form. Diastase, which catalyzes the conversion of starch to simple sugars, is found in malt, which comes from grain—usually barley. Prowashonupana—The Indians that Never Were Prowashonupana (“Prowash” for short) was developed during the 1980s by Robert F. Eslick, a plant breeder and agronomist at Montana State University who sought to improve barley for the benefit of Montana growers. He identified numerous genes that favorably altered various characteristics of Compana and Betzes, two barley varieties that are well adapted to Montana’s growing conditions. Through selective cross-breeding (applied genetics), he produced a number of new barley cultivars, including Prowashonupana, which turned out, to his surprise, to be exceptionally rich in beta-glucan. This caused quite a stir in barley circles. Commercial development of Prowashonupana began in 1996, but it has been grown on a large scale—mostly in Montana and other northern plains states—only since about 2002. But how did Eslick come up with that exotic name? It sounds vaguely Indian—could it be the name of a little-known tribe that once lived in Montana, or perhaps a traditional Indian name for Montana, meaning “Place Where Good Barley Grows”? (Actually, barley isn’t native to the Americas—Columbus brought it here.) No, a search through all known American Indian terms will come up dry. The truth is more prosaic. The name Prowashonupana was imaginatively cobbled together from English words that are relevant to barley:* *We are indebted to Dr. Christine Fastnaught, Technical Manager, Phoenix AgriResearch, Fargo, ND, for this information. She was a coauthor of the successful petition to the FDA to include barley in the labeling claim for the cardiovascular health benefits of beta-glucan soluble fiber. Pro – Protein. This cultivar is high in protein, mostly of a type called hordein (from the botanical name for barley, Hordeum vulgare), which is closely related to the gluten found in wheat, rye, and barley itself. Wa – Waxy starch. The starch in regular barley grains consists of two alpha-glucans; both consist entirely of glucose molecules, but they’re linked in different ways. About 25% is amylose (a straight-chain polymer), and about 75% is amylopectin (a branched-chain polymer). Barley grains that carry the “waxy” gene, however, are incapable of producing amylose, so their starch consists of 100% amylopectin. This gives the kernels’ interior a soft, waxy consistency, and it confers a variety of benefits for barley producers and their customers in the food and other industries. Sho – Short awns. In cereal-grain terminology, awns are the slender, bristly “hairs” at the tip of the plant. Barley awns can be very short to very long, depending on the variety. Nu – Nude. That’s right, there’s nude barley out there in plain sight of the children. It’s also called naked barley, but the term now preferred by most botanists is “hulless.” It’s not that hulless varieties don’t have the same kind of tough, hard hulls as are found in regular barleys—they do, but the hulls adhere to the kernels only weakly and come off easily in the combine during harvest, just as wheat hulls do. This desirable outcome yields the “nude” kernels with the outer bran layer intact, i.e., the whole grain. Unlike oats, in which most of the beta-glucan is concentrated in the bran, barley’s beta-glucan is distributed throughout the entire kernel, so even if the bran is polished off to make pot barley or pearl barley, there’s plenty of beta-glucan left to provide the health benefits. Pana – Compana. This barley variety was the parent of Prowashonupana, which carries the genes that were selected for in the cross-breeding experiments. Other new cultivars were based on the Betzes variety. There are many new waxy hulless varieties of barley with desirable properties. As invented names go, that one is pretty clever, no? Perhaps some Plains Indians should adopt it as their name for “really good barley that’s naturally rich in beta-glucans and that can help us be healthier and lose weight.” Beta-Glucan Is Very Viscous An extremely important factor in beta-glucan’s physiological effects is its high viscosity, which is related primarily to the length of its polymeric chains, each of which contains from about 20,000 to 1,000,000 glucose molecules.3 In the intestines, the viscous, gelatinous beta-glucan solution slows the digestion of foods and the absorption of nutrients, such as glucose—two good ways to minimize the glycemic index. These properties make beta-glucan-rich foods particularly well suited to patients who are obese or diabetic.4 The viscous beta-glucan may also prevent, to a degree, the absorption of some nutrients, including dietary cholesterol, and it may increase the conversion of cholesterol to bile acids (which, like cholesterol, are steroids).These actions may explain, at least in part, beta-glucan’s cholesterol-lowering effect. Barley Lowers Cholesterol Levels In last month’s article, we saw the results of a study in which naturally beta-glucan-rich barley flour made from Prowashonupana significantly reduced cholesterol levels in 12 healthy young men following a low-fat meal. Even regular barley is beneficial in this regard, however. Recently, researchers at the United States Department of Agriculture demonstrated that barley significantly reduced total cholesterol, LDL-cholesterol (the “bad cholesterol”), and triglycerides (fats), and it increased HDL-cholesterol (the “good cholesterol”), in 18 moderately hypercholesterolemic men who were on a low-fat, heart-healthy diet.5 They found that the results improved with increasing amounts of soluble fiber (beta-glucan) from barley and concluded that “These results indicate that the addition of barley to a healthy diet can reduce risk of cardiovascular disease.” Both beta-glucan and resistant starch significantly reduced postprandial glucose and insulin levels. The greatest effect was obtained, as expected, when the two were combined. Subsequently, the same USDA research group found similar effects of barley on total cholesterol and LDL-cholesterol (but not on triglycerides or HDL-cholesterol) in a group of 25 mildly hypercholesterolemic men and women on a low-fat, heart-healthy diet.6 And a study by researchers at the University of Minnesota and Cargill, Inc., showed reductions in total cholesterol and LDL-cholesterol, with no change in HDL-cholesterol and mixed results for triglycerides, in a group of 155 hypercholesterolemic men and women who received foods that had been enriched with barley beta-glucan.7 Barley Also Lowers Glucose and Insulin Levels Numerous studies have investigated the effects of beta-glucan on postprandial serum glucose and insulin levels, which must be kept under control if you wish to avoid type 2 diabetes, and especially if you already have type 2 diabetes or its common precursor condition, insulin resistance. Most such studies have shown a glucose-lowering effect of beta-glucan in diabetic patients but not in healthy individuals. Even if that were always true (but it’s not, as we are about to see), it would be reasonable to assume that healthy individuals might still benefit from beta-glucan-rich foods (notably barley) in terms of reducing their risk of developing insulin resistance. In any case, several recent studies have shown that beta-glucan can reduce glucose and insulin levels in healthy people too. Researchers in Italy gave 10 healthy young adults crackers and cookies made from whole wheat (which contains negligible amounts of beta-glucan) or barley (rich in beta-glucan).8 They found that the barley products elicited more favorable metabolic responses, resulting in lower values of the glycemic index, than the wheat products. Glucose and insulin levels were significantly lower with barley than with wheat, but there was no difference in triglyceride levels. In another study, researchers in New Zealand gave 18 healthy young men a high-carbohydrate breakfast that included a food or a beverage fortified with a highly enriched barley beta-glucan product.9 They found that the subjects’ glycemic response was significantly improved with the food, but not the beverage. With food, it’s presumed that the highly viscous beta-glucan decreases the mobility of glucose (and other) molecules in the intestine, thus retarding their absorption. The water in the beverage, however, would dilute the beta-glucan, diminishing its viscosity and allowing more rapid absorption of the glucose from the digested carbohydrates. Finally, the same USDA research group mentioned above studied the effects of both barley beta-glucan and a type of relatively indigestible starch called resistant starch on glycemic function in 20 middle-aged women—10 normal-weight and 10 overweight.10(Resistant starch is high in amylose and low in amylopectin; most starches have the opposite proportions of these two alpha-glucans.) They found that both beta-glucan and resistant starch significantly reduced postprandial glucose and insulin levels, with the greatest effect being obtained, as expected, when the two were combined. Eat the Humble Grain Be glad you’re not an elephant—trees are hard on the teeth, and they probably don’t taste very good either (but who knows?). Fortunately, barley is easy to eat, and its nutty flavor can be a treat. Best of all, it contains our good friend beta-glucan, whose solubility, viscosity, and relative indigestibility work together in wondrous ways to improve our health and help protect us from cardiovascular disease and diabetes. We should all look upon—and eat—the humble grain with newfound respect. References 1.    Higdon J. Fiber. Linus Pauling Institute, Corvallis, OR, 2005. 2.    Kim SY, Song HJ, Lee YY, Cho KH, Roh YK. Biomedical issues of dietary fiber β-glucan. J Korean Med Sci 2006;21:781-9. 3.    Fox GJ. High viscosity cereal and food ingredient from viscous barley grain. U.S. Patent 6238719, May 29, 2001. 4.    Lifschitz CH, Grusak MA, Butte NF. Carbohydrate digestion in humans from a β-glucan-enriched barley is reduced. J Nutr 2002;132:2593-6. 5.    Behall KM, Scholfield DJ, Hallfrisch J. Lipids significantly reduced by diets containing barley in moderately hypercholesterolemic men. J Am Coll Nutr2004;23:55-62. 6.    Behall KM, Scholfield DJ, Hallfrisch J. Diets containing barley significantly reduce lipids in mildly hypercholesterolemic men and women. Am J Clin Nutr2004;80:1185-93. 7.    Keenan JM, Goulson M, Shamliyan T, Knutson N, Kolberg L, Curry L. The effects of concentrated barley β-glucan on blood lipids in a population of hypercholesterolaemic men and women. Brit J Nutr 2007;97: 1162-8. 8.    Casiraghi MC, Garsetti M, Testolin G, Brighenti F. Post-prandial responses to cereal products enriched with barley β-glucan. J Am Coll Nutr 2006;25:313-20. 9.    Poppitt SD, van Drunen JDE, McGill AT, Mulvey TB, Leahy FE. Supplementation of a high-carbohydrate breakfast with barley β-glucan improves postprandial glycaemic response for meals but not beverages. Asia Pac J Clin Nutr2007;16:16-24. 10. Behall KM, Scholfield DJ, Hallfrisch JG, Liljeberg-Elmståhl HGM. Consumption of both resistant starch and β-glucan improves postprandial plasma glucose and insulin in women. Diabet Care 2006;29:976-81. Will Block is the publisher and editorial director of Life Enhancement magazine.