Overview
The term “beta-glucan” refers to a class of soluble fibers found in many plant
sources. The best documented use of beta-glucan involves improving heart health;
the evidence for benefit is strong enough that the U.S. Food and Drug
Administration (FDA) has allowed a “heart healthy” label
claim for food products containing substantial amounts of beta-glucan. Much weaker
evidence supports the potential use of certain beta-glucan products for modifying
the activity of the immune system.
Requirements and Sources
Beta-glucan is not an essential nutrient. It is found in whole grains (especially oats, wheat, and barley) and fungi such as baker’s yeast, Coriolus versicolor, and the medicinal mushrooms maitake and reishi.
Different food sources contain differing amounts of the various chemical constituents collectively called beta-glucan. Grains primarily contain beta-1,3-glucan and beta-1,4-glucan. Fungal sources contain a mixture of beta-1,3-glucan, and purified products containing only the 1,3 form are also available.
Therapeutic Dosages
For improving total and LDL cholesterol, studies have found benefit with beta-glucan at doses ranging from 3 to 15 grams (g) daily. However, benefits have been seen more consistently at the higher end of this range, and one carefully designed study found no benefit at 3 g daily.
Beta-glucan products can contain molecules of various average lengths (molecular weight). Some manufacturers claim superior benefits with either high or low molecular weight versions. However, one study failed to find any difference between high molecular weight and low molecular weight beta-glucan for normalizing cholesterol and blood sugar levels.
Therapeutic Uses
A substantial, if not entirely consistent, body of evidence indicates that beta-glucan, or foods containing it (especially oats), can modestly improve a person’s cholesterol profile. The most reliable benefits have been seen regarding levels of total cholesterol and LDL (low-density lipoprotein, or bad) cholesterol. Modest improvements of up to 10 percent have been seen in studies. Possible improvements in HDL (high-density lipoprotein, or good) cholesterol have been seen only inconsistently. It is thought that beta-glucan reduces cholesterol levels by increasing excretion of cholesterol from the digestive tract. This affects two forms of cholesterol: cholesterol from food, and, more important, cholesterol from the blood “recycled” by the liver through the intestines. However, virtually all studies involved oats and were conducted by manufacturers of oat products; independent confirmation remains minimal.
Beta-glucan may also modestly improve blood
pressure levels, though not all studies agree. In addition,
beta-glucan may help limit the rise in blood sugar that occurs after a meal. This
could, in theory, offer heart-healthy benefits, especially in people with
diabetes.
The other primary proposed use of beta-glucan products involves effects on the
immune system. Test tube, animal, and a few controlled studies in humans suggest
that beta-glucans can alter various measurements of immune function. In the
alternative medicine literature, these effects are commonly summarized as
indicating that beta-glucan is an “immune stimulant.” This description, however,
is an oversimplification. The immune system is extraordinarily complicated and, as
yet, incompletely understood. At the current level of scientific understanding, it
is not possible to characterize the effects of beta-glucan more specifically than
to say that it has “immunomodulatory” actions, or that it is a “biological
response modifier.” These intentionally unsensational terms indicate that it is
known that beta-glucan affects (modulates) immune function, not that it improves
immune function. Some of the immune-related effects seen in studies include
alterations in the activity of certain white blood cells and changes in the levels
or actions of substances, called cytokines, that modulate immune
function.
Based on these largely theoretical findings, as well a small number of very
preliminary human trials, various beta-glucan products have been advocated for the
treatment of conditions as diverse as allergic rhinitis, cancer,
infections, and sepsis (overwhelming infection following major trauma,
illness, or surgery). However, the evidence for actual clinical benefit remains
highly preliminary.
One study failed to find that beta-1,3-glucan (in topical gel form) was helpful
for treatment of actinic keratosis, a form of sun-induced precancerous changes
seen in aging skin. Another study found that it had no significant effect on
periodontal disease (gingivitis), an inflammation of the
gums caused by bacteria found in dental plaques.
Safety Issues
Beta-glucan, as a substance widely present in foods, is thought to have a high
margin of safety. However, if it really does activate the immune system, harmful
effects are at least theoretically possible in people with conditions in which the
immune system is overactive. These include multiple
sclerosis, lupus, rheumatoid arthritis, asthma,
inflammatory
bowel disease, and hundreds of others conditions. In
addition, people taking immunosuppressant drugs following organ transplantation
surgery could, in theory, increase their risk of organ rejection. However, there
are no reports as yet to indicate that any of these hypothetical problems have
actually occurred. Maximum safe doses in young children, pregnant or nursing
women, or people with severe liver or kidney disease have not been
established.
Bibliography
Davy, B. M., et al. “Oat Consumption Does Not Affect Resting Casual and Ambulatory 24-H Arterial Blood Pressure in Men with High-Normal Blood Pressure to Stage I Hypertension.” Journal of Nutrition 132 (2002): 394-398.
Jenkins, A. L., et al. “Depression of the Glycemic Index by High Levels of Beta-glucan Fiber in Two Functional Foods Tested in Type 2 Diabetes.” European Journal of Clinical Nutrition 56 (2002): 622-628.
Jenkins, D. J., et al. “Soluble Fiber Intake at a Dose Approved by the U.S. Food and Drug Administration for a Claim of Health Benefits: Serum Lipid Risk Factors for Cardiovascular Disease Assessed in a Randomized Controlled Crossover Trial.” American Journal of Clinical Nutrition 75 (2002): 834-839.
Keogh, G. F., et al. “Randomized Controlled Crossover Study of the Effect of a Highly Beta-glucan-Enriched Barley on Cardiovascular Disease Risk Factors in Mildly Hypercholesterolemic Men.” American Journal of Clinical Nutrition 78 (2003): 711-718.
Kirmaz, C., et al. “Effects of Glucan Treatment on the Th1/Th2 Balance in Patients with Allergic Rhinitis.” European Cytokine Network 16 (2005): 128-134.
Onning, G., et al. “Consumption of Oat Milk for Five Weeks Lowers Serum Cholesterol and LDL Cholesterol in Free-Living Men with Moderate Hypercholesterolemia.” Annals of Nutrition and Metabolism 43 (2000): 301-309.
Pins, J. J., et al. “Do Whole-Grain Oat Cereals Reduce the Need for Antihypertensive Medications and Improve Blood Pressure Control?” Journal of Family Practice 51 (2002): 353-359.
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