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Probiotics: An Old Story Takes on New Importance

By Betty Kamen, Ph.D.

In an age of aggressive antibiotics use, probiotics enhance not only digestion, but immune function as well.

Chances are that the term "probiotics" was not in Grandmother´s vocabulary, and she might have never heard of ƒlie Metchnikoff, the Nobel Prize-winning Russian scientist who "discovered" probiotics--those healthful microorganisms that set up shop in our digestive tracts.

What Grandmother probably did know, just like her mother before her, is that health is enhanced by eating fermented foods. She might have eaten sauerkraut, cottage cheese or yogurt, or perhaps she drank kefir, lassi or clabbered milk. If Grandmother lived in Asia, she might have enjoyed miso, tempeh, tamari, pickled daikon or kimchee. These fermented foods all promote better digestive health. She may not have known the mechanism, but she knew it worked.

Why do these foods work in our favor? Because they are excellent sources of probiotics: live bacteria that serve a protective rather than an antagonistic role in the human body. At home primarily in the intestinal tract, they are essential for proper digestion; they produce certain vitamins; they prevent the growth of pathogenic bacteria; and they help break down waste substances, toxins and invading organisms in the gut, to prepare them for elimination from the body. As such, probiotics improve immune function and overall health.

Probiotic literally means "for life," or supporting life. Our probiotic microorganisms are the essential "friendly" flora--especially, the "good" bacteria--that maintain the ecosystem in our bowel, or intestinal tract. Compare this concept with antibiotic drugs, which are designed to be "against life." Because antibiotics destroy "good bugs" along with the "bad bugs" (the pathogenic bacteria), we need to add probiotics to our diets if we have resorted to conventional antibiotics to treat infection, or if our immune systems have not been able to mount the necessary defenses to keep us healthy. We´ve heard this statement often, but what does it really mean? The answer lies in the vital role that intestinal tract flora play in our health.

A delicate balance

The human intestinal tract, or gut, is home to about 100 trillion bacteria of more than 400 species. Put all together, their total weight would come to almost four pounds. As with any highly populated society, some of the residents get along while others are antagonistic, but gut life goes pretty well as long as the "bugs" stay in their own neighborhoods, do their own thing and manage to keep competitors from moving in on their turf. A lot of areas of the gut are very densely "bug"-populated.

For example, in the colon (large intestine), several ounces of new bacteria are born every day and then leave through bowel elimination. Some of these guys are troublemakers. For example, a species of bacteria called Klebsiella pneumoniae occurs normally in the intestine, but if it escapes the gut it can cause serious respiratory infections. Others, such as species of Bifidobacterium, have probiotic effects: They produce a number of specialized acids which prevent colonization of the large intestine by invading bacteria, yeasts and some viruses; they help prevent toxicity from nitrates in foods; and they manufacture B vitamins.

Many bacteria also live in the small intestine, including the best known probiotics, the Lactobacillus species. These lactic-acid producing bacteria are important in acidifying the intestinal tract, as the Russian biologist ƒlie Metchnikoff discovered in the early 1900s. Intrigued by the relationship between the longevity of Bulgarians and their frequent consumption of cultured foods, especially yogurt, Dr. Metchnikoff researched these foods and was convinced that they help maintain the benign bacteria in the intestinal tract. He proposed that acid-producing microorganisms in fermented dairy products could prevent "fouling" in the large intestine, and thus lead to a prolongation of our life span. As hosts, we have an overall mutually beneficial, or symbiotic, relationship with most microflora. Dr. Metchnikoff also introduced the term dysbiosis (the opposite of symbiosis) to describe the state of imbalance in intestinal flora populations, which, he said, leads to disease.

When the natural balance of bugs in the gut is disturbed by events such as taking antibiotics or eating poor diets, our good bug neighborhoods can go bad. We can then experience malabsorption, which leads to malnutrition and immune system overload, and we end up chronically or acutely ill.

Conversely, having an adequate amount of acid-producing flora protects the gut from overgrowth of competing microorganisms. In fact, one of the reasons that probiotics are beneficial is that the acid they produce makes the gut environment hostile to disease-causing bacteria. Additionally, probiotic bacteria produce substances called bacteriocins, which are natural antibiotics that suppress populations of unfriendly flora. The fact is that we absolutely depend on certain bacteria--the friendly ones--to maintain many digestive and health functions. When the good guys are gone, parasites, unfriendly bacteria and yeasts, and certain viruses can grow out of control. Parasites also find it easier to take hold. For example, if you experience chronic fatigue, depression, stomach bloating, headaches, menstrual irregularities, skin rashes, low sex drive, joint or muscle pain, or other unexplained pain and digestive symptoms, you may be one of the millions of Americans afflicted by candidiasis, an overgrowth of the yeast Candida albicans. This occurs when the normal balance of intestinal bacteria is compromised.

While we usually think of probiotic bacteria as being only in the gut, we also host protective bugs in sites such as the oral cavity and the skin. This is why there are probiotic products for nose and upper throat (nasopharyngeal), skin and vaginal applications. Species such as L. plantarum, L. rhamnosus, L. paracasei, L. salivarius and L. acidophilus are common in human mucosa from the mouth to the rectum. But it is the flourishing of our friendly intestinal bugs that most affects our health.

A modern epidemic

What Metchnikoff could not have observed or predicted a century ago was how widespread dysbiosis and other digestive problems could become in a country such as ours in which the food supply is stable and plentiful, and malnutrition is thought to be "conquered." Amazingly, statistics tell us that up to one-half of our population has some type of gastrointestinal (GI) problem, including ulcers, gastritis, gastroesophageal reflux disease (GERD), gallstones, GI cancers and infections, irritable bowel syndrome (IBS), constipation and more.

Digestive problems are associated with many additional health conditions. You may be surprised to find out that ailments such as allergies, migraine headaches, asthma, eczema and other skin problems, vitamin deficiencies, chronic fatigue syndrome, certain eye problems, rheumatoid arthritis and other serious autoimmune disorders are linked to digestive ills. In fact, many alternative physicians are guided by the maxim, "All disease begins in the gut."

What is making digestive problems epidemic? Along with inadequate secretion of digestive enzymes, the primary cause is intestinal flora imbalance. The main causes of imbalance are high levels of chronic stress; foods low in nutritional value and fiber but high in sugars and processed components; the use of pharmaceuticals, especially the overuse of antibiotic drugs; and exposure to new microbes through, for example, travel and multiple sex partners. Other causes include inherited tendencies and a deficiency of gastric hydrochloric acid due to aging or compromised health.

Keep in mind also that gut bacteria are killed off by alcoholic beverages, preservatives in foods, chlorine in the water supply and many other substances. And don´t forget that "fast-food" eating habits--"inhaling" food without chewing and then washing it down with beverages that hamper digestion--make all digestive problems worse.

Digestion and immunity

Remember that, as a system, digestion is connected to other systems, including the immune system. The resident and transient friendly bacteria in our intestinal tracts--our "indigenous probiotics"--do more than maintain their neighborhoods. They are a front line in immune defense. In addition, they normalize serum cholesterol; they prevent and control gut infections; and they reduce the incidence of colon cancer and yeast infections. They also help the digestion of lactose; and they manufacture many vitamins, including some of the B-complex vitamins and vitamins A and K.

The major function of the intestinal tract is to digest and pass nutrients into the bloodstream to meet the body´s requirements for staying alive and healthy. Our indigenous probiotics have to work "24/7" to provide a constant defense against ingested toxins and unfriendly microorganisms in foods.

If these harmful substances aren´t intercepted, they can be absorbed through the intestinal wall into the body. When there isn´t an adequate or balanced population of intestinal flora (a state of dysbiosis), the intestinal wall becomes irritated and unable to discern exactly what should pass through. The result is increased intestinal permeability--called "leaky gut syndrome"--in which unnatural or harmful substances pass into the body and circulate in the bloodstream. Warning signs may include food allergies and intolerance, bloating, fluid retention, headaches, tinnitus, vertigo, brain fog, fatigue, weight gain, diarrhea and/or constipation, flatulence, IBS and other GI disturbances. This syndrome leads to a variety of health problems and has a crippling effect on normal immune defenses. When indigenous probiotic populations are imbalanced and leaky gut syndrome occurs, it is not only our digestion but also our immunity that is compromised. We often have an allergic response because our humoral immune defenses (the antibody producers) respond quickly to the foreign substances that pass through the leaky gut as antigens. But that´s not all. Our cell-mediated immune defenses, such as the ability of white blood cells to attack intruding organisms, are weakened, too. Research shows that the immunological activity of the gut-associated lymphoid tissue (GALT) represents approximately 60% of our immune system. (Lymph tissue traps and helps clear harmful toxins and pathogens.) The interaction of the GALT with immune-defense lymphocytes (a specific type of white blood cell) is very important. Clearly, then, the health of the intestinal wall is an important element in our total immunity.

Balance of intestinal flora is also associated with anticarcinogenic effects, one mechanism being detoxification. Studies show that milks fermented with certain probiotic strains are effective in deactivating certain risk factors of colon cancer. One strain of L. acidophilus, DDS-1, has been shown to inhibit the initiation of small tumors, possibly the result of an immune effect. The need to understand the relationship between intestinal health and cancer prevention is underscored by the fact that new colon cancer cases per year in the U.S. have reached about 150,000, and result in as many as 56,000 deaths annually. The recognition that digestive problems are epidemic brings home the importance of Dr. Metchnikoff´s century-old concept. Recent research confirms that probiotic Lactobacilli in the small intestine, and Bifido bacteria in the colon, strengthen the ability of immune cells in the gut lining to defend against harmful toxins, bacteria and allergens. Taking L. acidophilus and B. bifidum probiotic supplements concurrently can therefore help repopulate both the small intestine and the colon, and restore our intestinal environment to proper balance.

Probiotics to the rescue

The body´s need for probiotic bacteria, then, is an old story that takes on new importance today. Nearly every society has consumed some type of fermented food on a daily basis, and anthropologists theorize that this practice has been used widely by humans since prehistoric times. One reason is that fermentation is the safest and simplest way of preserving certain foods. Fermented milks are probably the best example of early "probiotics." In the hot climates of many countries, high temperatures would sour milk quickly. Eventually this process was done deliberately by heating milk and then cooling it to form a curd--in Turkish, a jugurt, which became "yoghurt."

Today, yogurt is produced in a more controlled process, with added live cultures of Lactobacillus acidophilus, Lactobacillus bulgaricus and other beneficial bacteria. Yogurt didn´t become popular in the U.S. until the late 1960s. At that time, the word acidophilus was so unfamiliar that people couldn´t remember it, let alone pronounce it. But after several decades (and many doses of antibiotics), the benefits of L. acidophilus and other "good bugs" have become clear. Nowadays, acidophilus and the umbrella term probiotics are part of our nutritional vocabulary.

As a vehicle for delivering probiotic bacteria, yogurt ranks high among consumers. It has been around long enough to convey a familiar, healthful image, and many brands taste delicious, thereby satisfying the palatability requirement. However, when sweeteners and flavors are added to yogurt, they can reduce its probiotic effect. Worse, when yogurt is pasteurized or heat-treated after culturing, most or all of the probiotic bacteria are killed. The yogurt label may say "contains live cultures," but you need to know whether live microbes were added after pasteurization. If microbes aren´t alive, they obviously cannot repopulate imbalanced intestinal neighborhoods.

Eaten alive

There is an important reason for the use of fermented dairy products as carriers of probiotic microbes. These foods are optimal environments for many probiotic microorganisms; thus, they can be adapted to ensure sufficient survival of added probiotic bacteria. Individuals who avoid dairy products because they are "lactose intolerant" may hesitate to try dairy-based probiotic foods. (Lactose intolerance, or lactose maldigestion, is the inability to break down lactose, a sugar, in the small intestine; so it passes into the colon, where bacteria feed on it, producing gas.) However, many people with lactose intolerance find that they have better tolerance of fermented milk products than plain milk. This is due to an enzyme in these products called §-galactosidase, which is known to reduce the symptoms of lactose intolerance.

Even so, some of the most effective probiotics are preparations of "liquid acidophilus"(usually found only in the refrigerated sections of natural food stores). These products combine L. acidophilus with other probiotic bacteria used in culturing yogurt, especially L. bulgaricus, L. caucasicus, S. thermophilus and others. The liquid preparations generally contain more concentrated and viable (live) cultures than yogurt.

A typical recommended amount to take might be at least one to two billion colony-forming units (CFUs) of microbes. But how many live and appropriate bacterial species and strains are available for you to ingest? A more essential measure of effectiveness than just the number of microbes is the actual probiotic effect the product exhibits. Try contacting the manufacturers of your favorite probiotics to ask whether this information is available. Also, a little self-test may work for you: It is said that if you take several times the usual amount of a probiotic, you´ll get temporary gas and bloating some hours later--a rather sure sign that the microbes in the product you ate were alive and well. Most probiotics available today boast large numbers of CFUs of live bacteria. But remember, to be effective, probiotic microbes must remain alive and vigorous in the medium in which they are offered. Probiotic makers have to consider many factors: the chemical composition of the culture medium; the possible interactions of microbes with each other and with the starter culture; the physical conditions of product storage; and the ability of different bacteria to survive shelf life. Probiotic foods and supplements containing live bacteria must be cooled during storage. Refrigeration is necessary to guarantee stability and high survival rates of microbes (unless new technologies are utilized to maintain viability, such as "hibernation"--leaving the bacteria in an inactive resting state until they are exposed to fluids).

Safety is also a factor in product quality. Because many of the bacterial species are originally isolated from infection sites, verification of the safety of commercial probiotic foods and supplements is important. The safety of probiotic microbes that have been used traditionally has been confirmed through a long period of experience. Various species of Lactobacillus, Leuconostoc, Pediococcus and others have been used extensively and safely in food processing. Today´s probiotic foods and supplements are mainly members of the genera Lactobacillus and Bifidobacterium.

There also a few "good" Streptococci, especially S. thermophilus. And there are Enterococcus faecium, Lactococcus cremoris and the yeast Saccharomyces boulardii. The risk of lactic-acid bacterial infection or fungal infection from S. boulardii subspecies is very low. One caveat concerns certain strains of L. rhamnosus, which still warrant surveillance and careful processing.

Another challenge is that microbes must survive after entering the GI tract. The main obstacles are gastric acidity and the action of bile salts. So, in determining how to deliver live microbes, probiotic makers must assess the microbes´ ability to tolerate bile and low stomach pH. They must also assess the "staying power" of the microbes--their ability to adhere to the intestinal mucous membranes--and the environment of the human intestinal tract, including typical oxygen content and water quality.

Just as unknowns in the culture medium can enhance or destroy probiotics, so can the gut environment. To protect the microbes from stomach acid, one new probiotic delivery approach involves surrounding the bacteria with gel-forming polysaccharides. The making of stable, viable probiotic products certainly takes more than tossing a batch of friendly microbes into a culture medium.

Another way to increase the viability and growth of ingested probiotics is to feed them prebiotics. These are food substances not digested by us, but instead utilized as food by probiotic microbes. Present evidence concerning the two most studied prebiotics--fructooligosaccharides (FOS) and inulin (types of plant-based sta ches)--indicates that they are resistant to digestion by gastric acid and pancreatic enzymes. By the way, FOS is known to help decrease triglycerides; stimulate absorption of several minerals (particularly calcium, magnesium, zinc and iron); to improve mineralization of bones; and to improve glucose control.

To alleviate serious bowel disturbances, to rebuild impaired health or immunity, or to reestablish healthy gut flora after antibiotics and other interventions, it is in one´s best interest to take probiotics daily, whether from a food or supplement source. Keep in mind that to obtain a continuous probiotic effect, one must continually consume additional exogenous (from an outside source) probiotic cultures, rather than rely on our endogenous supply to reproduce itself. The more serious one´s health problems, the more imperative it is to consult with qualified health practitioners, nutritionists and probiotic makers about the benefits of various probiotic strategies.

Some researchers say that the use of probiotics is one of the most important medical stories to emerge in nutrition and gut microbiology since the turn of the 19th century. Groups in Europe have long been working on either treating or preventing specific diseases with customized probiotics. New probiotic foods and supplements are showing up in U.S. pharmacies and natural food stores. For example, supplements containing soil-based microflora such as Bacillus laterosporus and Bacillus subtilis are becoming available and continue to be studied. In the future, expect to see more choices of viable probiotics, with additional species and strains of friendly bacteria added as research proves their probiotic efficacy.

Next issue: a survey of different probiotic products.

Many Beneficial Effects

L. acidophilus has long been used to help repopulate friendly intestinal bacteria and for a variety of other therapeutic applications. These include reducing the recurrence rate of infections such as urinary tract infections (UTIs), cystitis (bladder inflammation) and vaginal infections; alleviating IBS problems; and enhancing immune function.

Different probiotics not only modulate the immune response to harmful agents, but can also help normalize hypersensitivity reactions. New studies have demonstrated the effectiveness of probiotics in the management of food allergies. Probiotic therapy is known to reverse some immunologic disturbances characteristic of inflammatory conditions. Several ways that probiotics alter immune responses during the course of allergic inflammation in the gut are that they reduce the secretion of inflammatory substances; they make the intestinal gut less permeable; they normalize the composition of the intestinal microflora; and they enhance the production of beneficial immune cells. Oral introduction of L. casei and L. bulgaricus has been shown to activate the production of macrophages, cells that play an important role in immune defense.

Taking probiotics helps the body resist pathogens, including viruses, E. coli and intestinal parasites. Researchers at the University of California at Berkeley suggested that a cup of live-culture yogurt a day may help keep the bad bugs away. They had 60 people eat either a cup of live-culture yogurt, pasteurized yogurt, or no yogurt every day for a year. People who ate either type of yogurt had fewer colds and flu than those who ate no yogurt at all. Other research indicates that taking live-culture yogurt or supplementing with L. bulgaricus stimulates the production of higher-than-average levels of gamma-interferon, a crucial immune system component. Studies in the Netherlands have reiterated the finding that intestinal microflora have great influence on infectious diseases by proving that, in addition to controlling the growth of opportunistic microorganisms, friendly flora have a key role in stimulating the immune system.

Probiotics have shown beneficial effects against inflammatory bowel disorders, including ulcerative colitis and Crohn´s disease. In these cases, when we talk about probiotics, we can include another beneficial bug, a yeast named Saccharomyces boulardii. It is available in supplement form and has been found to be effective in reducing diarrhea and inflammation in Crohn´s disease and other conditions. S. boulardii has also been shown to prevent further recurrence of Clostridium difficile-associated diarrhea. And in a double-blind study of critically ill, tube-fed patients, the probiotic S. boulardii was found to prevent diarrhea.

Another example of probiotic effect is demonstrated by a change in the concentration of bacterial urease (enzymes that indicate the metabolic activity of gut microflora). Analyses of fecal urease concentrations have shown elevated levels in patients with juvenile chronic arthritis. In such inflammatory states, oral probiotic therapy has normalized fecal urease. Probiotic therapy appears to stabilize the gut microbial environment and prevent release of inflammatory substances, a response of the gut-associated lymphoid tissue that can disrupt intestinal integrity. Other studies indicate that fecal enzyme activities and stool consistency may improve after oral Lactobacillus GG administration.

While it is widely accepted that probiotics are important during and after a course of antibiotics, it is less known that probiotics are an essential part of treatment for candidiasis in both women and men. Candidiasis is a systemic infection, but it often reveals itself in women as a vaginal infection; in men, its telling signs include "jock itch," athlete´s foot and skin rashes. If you´re you still not concerned about how your friendly flora are doing, consider this: In Candida´s advanced stage, the yeast can colonize around internal organs, including the heart--a deadly phenomenon much more prevalent in men than in women.

Betty Kamen´s new book on female sexuality--She´s Gotta Have It!: Sexuality, Euphoria, Orgasm--is now available in bookstores and on her website at Betty Kamen, Ph.D., has been reporting breakthroughs in nutrition and medicine for more than 25 years. Many of Dr. Kamen´s newsletters and special reports on new products are also available on her website. You can sign up for a free daily online, one-line Table Talk Nutrition Hint by e-mailing your request to

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