A Probiotics Primer

A Probiotics Primer

This section is compiled by Frank M. Painter, D.C.
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From the June 1999 Issue of Nutrition Science News

By David Wolfson, N.D.

Ever since Louis Pasteur formulated the germ theory of disease in the late 1800s, humans have been locked in mortal combat with microorganisms. The zealous use of antibiotics, disinfectant chemicals and sanitary packaging attests to our fear and loathing of all things microbial. In this age of antisepsis, it seems ironic that each of our intestinal tracts harbors tens of trillions of bacteria. This number, by some estimates, exceeds the total number of cells making up the human body. Even more ironic is that many of these bacteria are beneficial. Probiotic--or life-enhancing--organisms within the intestinal tract perform such a wide variety of physiological functions that they have been likened to an accessory organ.

To understand how probiotics influence health, it is important to understand how they function within the intestinal tract. The following is an overview of several major characteristics and functions of probiotic organisms.

Pathogen antagonism.   Perhaps the most important function of probiotic organisms is to limit the growth of pathogenic organisms. These potentially harmful microbes naturally reside in the human intestinal tract but do not overpopulate when sufficient numbers of probiotic organisms are present. Probiotic bacteria not only compete with these pathogens for nutrients and space, they also secrete substances--lactic acid and other organic acids, hydrogen peroxide, and potent antibiotic agents known as bacteriocins--that inhibit the growth of harmful organisms. [1,2] Many studies demonstrate the ability of probiotics to antagonize pathogenic microbes [3,4] and treat the intestinal infections caused by these harmful organisms. [5-7]

Lactobacillus bacteria reside mainly in the small intestine, bifidobacteria in the large.

Food digestion.   Probiotic organisms contribute to the digestive process by secreting enzymes that help break down foods. [8,9] Probiotics help digest food in the gut in the same way they partially digest the carbohydrates, proteins and fats in milk to create yogurt (in fact, people who are lactose intolerant can often tolerate yogurt because the lactose has already been partially broken down). Improved digestion can benefit anyone with impaired secretion of hydrochloric acid, bile, and pancreatic or intestinal enzymes.

Short-chain fatty acid (SCFA) production.   Among the most important by-products of probiotic metabolism are SCFAs. SCFAs, such as lactic acid, provide up to 70 percent of the energy required by intestinal epithelial cells and have been used therapeutically for disorders such as inflammatory bowel disease. [10] Intestinal cells appear less capable of being a protective barrier without the energy provided by SCFAs.

SCFAs provide additional health benefits by making intestinal pH more acidic. Because most intestinal pathogens do not grow well in an acidic environment, their populations are kept in check. In addition, lower intestinal pH facilitates absorption of minerals such as calcium, magnesium and zinc. [11,12] Lowering intestinal pH may also help lower colon-cancer risk. Studies have shown that low-risk groups typically have a lower fecal pH, while high-risk groups tend to have a higher fecal pH. [13,14]

Immune enhancement.   Probiotic flora have a profound effect on immune function by enhancing both the cell-mediated and humoral branches of the immune system. Research studies show that probiotic organisms increase numbers of circulating white blood cells, [15] stimulate phagocytosis, [16] elevate levels of antigen-specific antibodies [17] and increase production of such cytokines as gamma-interferon. [18] One recent Lancet study of 4,718 women associates low levels of lactobacilli in the vaginal tract with increased incidence of HIV-1 in younger women. [19] Findings like these drive home the importance of maintaining healthy flora to ensure proper immune function.

Food-allergy reduction.   The intestinal lining prevents movement of toxic/allergenic materials into the bloodstream. An imbalance of intestinal flora can contribute to increased intestinal permeability--the so-called "leaky gut syndrome." Intestinal hyperpermeability has been implicated in a variety of diseases including hypersensitive reactions to foods. [20] A recent landmark study in the Journal of Allergy and Clinical Immunology made clear the connection between intestinal flora and food allergy. Using a strain of Lactobacillus rhamnosus, researchers observed clinical improvements in a test group of 10 infants with food-allergy-related dermatitis. After a one-month trial, infants on the probiotic supplement showed significant improvements in their condition compared to infants given placebo. The authors conclude that enhanced intestinal barrier function leading to decreases in antigen translocation were responsible for the clinical improvements seen in the infants. [21]

Anticarcinogenic activity.   Research is uncovering anticarcinogenic activities that can be partially explained in terms of functions already discussed, such as lowering intestinal pH, reducing populations of toxin-producing bacteria, and enhancing immune function. The organic acids produced by probiotics also have a mildly stimulating effect on gut peristalsis, [22] hastening the removal of potentially carcinogenic toxins from the intestinal tract. Recent research has even shown that cell-wall components of certain probiotic organisms may promote specific immunological activity against malignant cells. [23] In one animal study, Bifidobacterium longum was shown to inhibit mammary and liver carcinogenesis. [24] This study is exciting because it suggests the anticarcinogenic activity of probiotics may extend beyond the intestinal tract.

Making the Sale

Helping customers choose a probiotic supplement can be tricky. Numerous products are on the market, all packaged differently, promising different benefits, containing different types and numbers of organisms, and all with different price tags. To make sense of the array of products, advise customers to consider the following:

Species.   The most reliable and well-researched probiotic organisms belong to either the lactobacillus or bifidobacteria genera. I recommend products that contain one or more species from both genera for coverage in both the small and large intestine (see sidebar). Other beneficial species include Streptococcus thermophilus (an organism frequently found in yogurt) and Enterococcus faecium (not to be confused with the pathogenic Enterococcus faecalis). Products containing these organisms can be helpful but should also contain lactobacillus and bifidobacteria species.

Refrigeration.   My advice is to avoid unrefrigerated products. Probiotics are living organisms that die at a much faster rate when not refrigerated. A recent study by the National Nutritional Foods Association in Newport Beach, Calif., found that about 50 percent of the probiotics available in retail stores contained significantly fewer viable bacteria than claimed on the label. [25] A big part of this problem is lack of refrigeration. This does not mean unrefrigerated organisms will die immediately, but over the course of weeks or months, and especially at warmer temperatures, significant numbers of probiotic organisms will die.

Desiccants.   Another factor that leads to rapid die-off in powdered probiotic products is moisture. Exposure to moisture occurs every time the container is opened. To help minimize moisture damage, some manufacturers add a small desiccant bag to the product. If the probiotic you sell does not contain a desiccant, I recommend you either carry another product, call the company and recommend they adopt this inexpensive practice or recommend customers add their own desiccant to the product after opening it. Desiccant can be found at some photographic equipment stores or industrial supply houses.

Stability.   Freeze-drying is another method of maintaining product stability. This process, also called lyophilization, is a standard, accepted practice in the probiotics industry. Properly done it does not cause significant harm to the organisms. Products that are not freeze-dried, such as liquid probiotics supplements or yogurt, have a much shorter shelf life. If your customers think it will take longer than a few weeks to finish the supplements, recommend they purchase a powdered, freeze-dried product.

Potency.   Probiotics are usually measured in numbers of organisms per gram. High-potency products typically contain 4 billion or more organisms per gram. If the product is encapsulated, the label should provide some indication of how many organisms each capsule contains. An expiration date on the label should indicate how long the product will retain its stated potency.

Fructo-oligosaccharides.   Some probiotic products contain a type of nondigestible carbohydrate known as fructo-oligosaccharides (FOS). I believe these products have a distinct advantage over other products. FOS can be considered a prebiotic--a nutritional substance that preferentially feeds probiotic organisms, enabling them to outpace the pathogens and, ultimately, leads to a beneficial balance of good and bad flora. FOS are so effective at increasing numbers of intestinal bifidobacteria that some researchers believe taking a prebiotic is as effective at replenishing intestinal flora as is taking a probiotic. [26]

Means to an End

Once your customers have decided which product to buy, they'll probably want to know how to take it. How a probiotic is taken depends on why it is being taken. If the primary reason for taking the probiotic is to aid digestion, it should be taken with meals. But if the goal is to have the probiotic reach the lower intestinal tract, I recommend it be taken between meals with a full glass of water because water dilutes the acids of the stomach and moves the organisms quickly into the intestinal tract. Of course, probiotics can be used for both purposes by taking some with meals and some between meals.

The next question you are likely to hear is how much to take. Since probiotics are generally nontoxic, the dose can vary widely, but here are some guidelines to recommend. If the probiotic is being taken for maintenance or preventive purposes, a reasonable dose would be between 1 billion organisms two or three times weekly and 4 billion organisms daily. For therapeutic purposes, such as fighting an intestinal infection, coping with an illness, or after a course of antibiotics, an effective dose would be 5 billion to 10 billion organisms two or three times daily. These doses are for adults and children older than 12. For younger children, recommend your customer consult with a health care practitioner.

Given their broad spectrum of benefits, it seems likely that probiotic supplements will one day be considered as important to daily nutrition as vitamins, minerals and antioxidants.


Bacterial Allies


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23. Miller-Catchpole R. Bifidobacteria in clinical microbiology and medicine. In: A. Bezkorcvainy, editor. Biochemistry and physiology of bifidobacteria. Boca Raton (FL): CRC Press; 1989. p 179-99.

24. Reddy BS, et al. Inhibitory effect of Bifidobacterium longum on colon, mammary, and liver carcinogenesis induced by 2-amino-3methylimidazol-[4,4-f]quinoline, a food mutagen. Cancer Res 1993;53(17):3914-8.

25. National Nutritional Foods Association. Minutes of the Probiotics Interest Group Meeting. Las Vegas, NV, 1993.

26. Gibson GR, et al. Dietary modulation of the human colonic microbiota: introducing the concept of prebiotics. J Nutr 1995;125(6):1401-12

David Wolfson, N.D., is a naturopathic physician, nutrition educator and writer, as well as a consultant to the natural products industry

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