May 2014 Issue
Betting on Beta-Glucans
By Densie Webb, PhD, RD
Vol. 16 No. 5 P. 16
Research suggests this type of fiber can improve blood glucose control, insulin resistance, and cholesterol levels.
Chances are that many of your clients aren’t getting enough fiber in their diets despite the constant admonitions to increase their consumption. What your clients may not know is that not all dietary fibers are created equal, both in terms of chemical structure and potential health benefits.
Soluble and insoluble fibers are the most commonly recognized categories of fiber, but each can be divided into many subcategories depending on the food source, molecular weight, and resistance to digestion. What’s more, their effects on health can be just as diverse.
One type of fiber that has received much attention lately is beta-glucan, a glucose polymer found in the cell walls of cereals (eg, oats, barley), certain types of mushrooms (eg, reishi, shiitake, maitake), yeasts, seaweed, and algae. A lesser amount is found in wheat, rye, and sorghum. Among these sources, barley typically has the highest beta-glucan content and oats the second highest. One and a half cups of cooked oatmeal or three packets of instant oatmeal provide 3 g of beta-glucans; 1 cup of cooked pearl barley contains approximately 2.5 g of beta-glucans.
Beta-glucans have been the subject of intensifying research because they may have beneficial roles in lowering insulin resistance and blood cholesterol, reducing the risk of obesity, and boosting the immune system to fight cancer.1,2
For the past eight years, health claims for beta-glucan–containing foods have been allowed in the United States, Canada, Sweden, Finland, and the United Kingdom. The health claims approved by the FDA and the European Food Safety Authority are based on research showing that consuming 3 g of beta-glucans per day, from either oats or barley, can lower blood cholesterol levels by 5% to 8%.3 Clients or patients with high cholesterol levels likely will see the greatest benefit.4 However, it isn’t clear whether beta-glucans can lower triglyceride levels.
While some studies have suggested that beta-glucans also may boost the immune system, increase satiety, help regulate blood glucose levels, and decrease the risk of developing some types of cancer, the research hasn’t been consistent enough to determine specific daily requirements for optimal health. Focusing on a recommendation for overall health is complicated by the fact that not all beta-glucans are created equal.
“Oat and barley foods have been shown to reduce the risk of glucose intolerance by slowing glucose absorption after a meal,” says Susan M. Tosh, PhD, a research scientist with Agriculture and Agri-Food Canada, an organization that provides information, research, and technology programs and policies related to food and agriculture. “One study followed more than 65,000 women for six years and found that dietary fiber, including beta-glucan intake, was inversely associated with the development of type 2 diabetes.5 Mushroom beta-glucans differ structurally and don’t affect glucose absorption.” However, a recent laboratory study suggested that beta-glucans from barley and mushrooms have the potential to decrease glycemic response between 20% and 25% and 17% and 25%, respectively.6
While some studies suggest that a boost in immunity markers occurs from consuming oat beta-glucans,7 most of the research on beta-glucans and immunity has been done on mushroom extracts, not oats or barley. Medicinal mushrooms, especially Coriolus versicolor (known as yun zhi in China), commonly are used in traditional Oriental medicine and have been for centuries.8,9 In the 1980s, the Japanese government approved the use of protein-bound polysaccharide (PSK), a beta-glucan compound found in mushrooms, for treating several types of cancers and for widespread use in cancer immunotherapy.9 Rather than directly killing cancer cells, these mushroom beta-glucans are thought to stimulate immune responses that damage cancer cells.8 However, because PSK is bound to a protein, pure beta-glucans that have been separated and purified may act differently than beta-glucans from food.10
While animal studies suggest that beta-glucans may be helpful as an adjuvant therapy,9,11 there’s no research that shows increasing intake of PSK or any other beta-glucans can help prevent cancer. Most of the research on PSK and Coriolus has been done in Japan, and most of it has been done on PSK isolated from mushrooms rather than on PSK-rich mushrooms as part of the diet. “I would recommend foods rich in beta-glucans for blood glucose control and lipid lowering,” says Joanne Slavin, PhD, RD, a professor of food science and nutrition at the University of Minnesota. “I’m not convinced that beta-glucans would change immune function.”
In other studies, researchers have examined the association between beta-glucans and weight. But whether consuming beta-glucan–rich foods aids in weight management isn’t clear. For example, one study found that consuming a beverage containing 2.5 g of beta-glucans resulted in significantly greater ratings of satiety than a fiber-free beverage.1,12 Another study found that overweight men who consumed 7 g/day of beta-glucans for 12 weeks experienced a significant reduction in body mass, waist circumference, and visceral fat compared with those in the placebo group.1,13
Research has suggested that a minimum of 4 to 6 g of beta-glucans are needed for appetite suppression.1 However, another study found that consuming 9 g/day of beta-glucans for 24 weeks had no significant effect on body weight.14 A recent review concluded that beta-glucans significantly increased satiety and reduced appetite compared with a diet containing no beta-glucans, although it didn’t always translate into decreased food intake in short-term studies.15
How Beta-Glucans Work
Many plant-derived polysaccharides, such as beta-glucans, regulate the immune system as they pass through the intestinal tract.16 Some beta-glucans interact with immune cells and stimulate the immune system directly.17
Viscous fibers such as psyllium, beta-glucans, and pectin may form a gel in the small intestine, which acts to delay nutrient absorption, slowing the delivery of glucose into the bloodstream and reducing the need for insulin. These fibers’ ability to lower postprandial glycemia and insulinemia, as well as cholesterol, has been established in numerous studies, but long-term effects are less well known. Bacteria ferment beta-glucans in the intestinal tract, producing short-chain fatty acids. These may stimulate insulin release from the pancreas and alter glycogen breakdown by the liver and therefore play a role in glucose metabolism and protect against insulin resistance.1 However, it’s unknown whether appetite suppression is the result of increased fullness or an effect of insulin regulation.15
Advice for Clients
Beta-glucans are present in various commonly eaten foods, and intake is believed to be safe for most people. However, if beta-glucans can stimulate the immune system, this could theoretically pose problems for people suffering from autoimmune conditions, such as multiple sclerosis, lupus, rheumatoid arthritis, asthma, and inflammatory bowel disease. Researchers don’t know what the effect of consuming large amounts of beta-glucans may be on these conditions. According to Gregory J. Berry, MBBS (SYD), MRCPych, a Sydney, Australia-based medical research analyst, “If a patient is going to proactively immunomodulate with these compounds, they should first consult with their physician.”
Slavin recommends that people increase their consumption of foods rich in beta-glucans, as long as they know they’re consuming concentrated sources of beta-glucans.
“Beta-glucans are the new frontier in medicine,” Berry says, but “much research still remains to be done.”
— Densie Webb, PhD, RD, is a freelance writer, editor, and industry consultant based in Austin, Texas.
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2. Thompson IJ, Oyston PC, Williamson DE. Potential of the beta-glucans to enhance innate resistance to biological agents. Expert Rev Anti Infect Ther. 2010;8(3):339-352.
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14. Pick M, Hawrysh Z, Gee M, Toth E, Garg M, Hardin R. Oat bran concentrate bread products improve long-term control of diabetes: a pilot study. J Am Diet Assoc. 1996;96(12):1254-1261.
15. Clark M, Slavin J. The effect of fiber on satiety and food intake: a systematic review. J Am Coll Nutr. 2013;32(3):200-211.
16. Ramberg J, Nelson E, Sinnott R. Immunomodulatory dietary polysaccharides: a systematic review of the literature. Nutr J. 2010;9:1-60.
17. Vetvicka V, Thornton B, Ross G. Soluble β-glucan polysaccharide binding to the lectin site of neutrophil or natural killer cell complement receptor type 3 (CD11b/CD18) generates a primed state of the receptor capable of mediating cytotoxicity of iC3b-Opsonized target cells. J Clin Invest. 1996;98(1):50-61.
18. Salmeron J, Manson JE, Stampfer MJ, Colditz GA, Wing AL, Willett WC. Dietary fiber, glycemic load, and risk of non-insulin-dependent diabetes mellitus in women. JAMA. 1997;277(6):472-477.