PROBIOTICS
By: Peilin Guo, MS, RD
Beneficial bacteria are considered the most commonly consumed functional foods worldwide. Although the words “culture” and “starter” are not well understood by many Americans, foods fermented with beneficial bacteria, such as yogurt, cheese, Kefir and sauerkraut have been a part of our diet since ancient times. Another term for beneficial bacteria is “probiotics.”
According to Schrezenmeir and de Vrese, fermented foods were expected to prolong the life span of Europeans as early as the 1800s. Metchnikoof was recognized as the true grandfather in understanding and conveying the health benefits of beneficial bacteria. Today, numerous scientific studies demonstrate that probiotic bacteria and foods fermented with beneficial organisms have a variety of health benefits.
Probiotic Basics
There are hundreds of different bacterial species inhabiting the human gut, most being anaerobic. Although the intestines of a fetus are free from bacteria, the colonization of newborns’ intestines starts immediately with delivery through the birth canal. The composition of intestinal microflora varies from one person to another depending on a person’s diet, age, medication, stress levels and physiological conditions. While Bfidobacterium infantis and B. breve are often the predominant friendly bacteria in infants, the proportion of bifidobacteria in breast-fed infants is higher than that of bottle-fed babies. Breast-fed infants, for example, have more Bifidobacterium and fewer Enterococci than formula-fed babies.
Among the hundreds of bacterial species in the human digestive tract, some are potentially pathogenic or putrefactive, while others (probiotics) are friendly. The term probiotics is derived from the Greek word meaning "for life.” This is in direct contrast to the term we are all familiar with, “antibiotics.” ”Lactic acid bacteria (LAB)” is also used for probiotic bacteria because most produce lactic acid. Currently, there is not a standard definition for probiotics. However, probiotics can be defined as:
“Viable organisms in a supplement or food form that exert health effects on the host when consistently ingested.”
Probiotic bacteria are usually Gram-positive, nonsporing and anaerobic. Probiotics are found in fermented or fortified foods, and also in supplements (see Table 1).
To qualify as probiotics, the organisms should meet the following criteria:
Be safe to the host after ingestion
Provide health benefits to the host
Be able to survive the transit through the stomach and upper small intestine in order reach the lower gastrointestinal tract and colon
Be produced in commercial scale, stored and delivered to the host intestine
Table 1. Organisms Considered as Probiotics and Their Sources
|
Probiotic Bacteria Species |
Major Distribution and Uses |
Note |
|
Lactobacillus |
Many species of this genus well documented. |
Commonly used in foods and supplements |
|
L. acidophilus |
Intestine and vagina; fermented milk drinks, feed additive, supplements |
Able to implant in the small intestine; documented therapeutic use |
|
L. bulgaricus |
|
Transient or non-implanting flora in human intestine |
|
L. breve |
Fermented foods, supplements |
|
|
L. casei |
Mouth, cheese, fermented milk, kefir, supplements |
Able to implant in the small intestine; documented therapeutic use |
|
L. jugurti |
Yogurt, fermented milk drinks |
|
|
L. helveticus |
Cheese, yogurt drink, kefir |
|
|
L. plantarum |
Fermented foods, supplements |
Able to implant in the small intestine |
|
L. rhamnosus |
Supplements |
Able to implant in the small intestine |
|
Bifidobacterim |
More than 30 species have been isolated. Most species in this genus are human origin. |
Strictly anaerobic; requires more complex carbohydrates as nutrients;
some species are well documented |
|
B. bifidum |
Intestine of humans, especially infants; fermented milk drinks, supplements |
High level in infants |
|
B. infantis |
Intestine of infants, fermented milk drinks, supplements |
Prevalent in infants |
|
B. longum |
Intestine of infants, fermented milk drinks, supplements |
In the lower small intestine of both adults and children |
|
B. adolescentis |
Intestine of adults |
|
|
Streptococcus |
Previously called Lactococci. |
Most commonly used in fermented foods |
|
S. lactis |
Butter, cheese, yogurt |
Transitory, do not implant in human intestine; produces nisin used mostly
for food preservation; Needs to be consumed constantly |
|
S. thermophilus |
Butter, cheese, yogurt |
Transitory, needs to be consumed continuously |
|
Pediococus |
Commonly used to ferment meat, sausages, silage |
A late comer in probiotic application |
|
P. acidilactici |
Meet, sausages |
|
|
Streptococcus |
|
|
|
Enterococcus faecium
(F.K.A. S. faecium) |
Has been used in supplements, but concerns have been raised due to its potential in communal infections. |
A normal habitant of the human gut |
|
Lactococcus |
|
|
|
L. diacetylactis |
Cultured butter milk, cultured cream, kefir |
Produces diacetyl; showing indication in probiotic uses |
|
Saccharomyces boulardii (yeast) |
Supplements; reported to be effective in minimizing infection-associated diarrhea |
|
Health Effects of Probiotics
The concept of probiotics was introduced by Metchnikoff in the early 1900s. However, scientific studies on the health benefits of probiotic bacteria did not begin until the 1960s. In recent years, there has been a dramatic increase in scientific work confirming the prophylactic and therapeutic effect of consuming foods or supplements that contain probiotics. Currently, probiotics are not only widely used by health food consumers, they have also attracted the interest of health care professionals, especially clinicians whose interest in antibiotics have diminished.
Friendly probiotic organisms protect the host in many ways. Among its many numerous benefits, probiotics are extraordinary for people who consume little fiber or fermented foods, are taking antibiotics, have repeated intestinal or vaginal infections, or travel frequently. For those who simply want to maintain their well-being or strengthen their intestinal immune system, probiotic products are something to strongly consider.
The effects and supporting studies and clinical trials include:
Reducing antibiotic-associated infections and diarrhea: Millions of antibiotic prescriptions are written annually for treating infection-related conditions. Diarrhea is a common side effect that follows antibiotic treatment. This vicious cycle normally continues. Stronger antibiotics are continuously developed for resistant pathogenic stains. Antibiotics are broad-spectrum killers that destroy both pathogens and beneficial bacteria residing inside the intestinal tract. Since pathogenic bacteria tend to develop a resistance to antibiotics quickly, they can grow uncontrolled, resulting in further infections. Probiotics such as L. acidophilus, B. longum and Saccharomyces boulardii are very promising in preventing and reducing antibiotic-associated diarrhea (AAD) caused by Clostridium difficile, Staphylococcus, Klebsiella and Candida species. Probiotics suppress the growth and propagation of pathogens. Hence, they reduce the incidence of severe diarrhea.
Reducing the incidence and severity of infections and diarrhea: Probiotic bacteria also reduces the primary infections in both experimental and clinical settings. In a double-blind, randomized trial with children attending day care, Hatakka and associates observed that children who consumed milk fermented with Lactobaciullus (rhamnosus) GG daily had significantly fewer days of absence from day care due to illness. There was also a reduction in the number of children suffering from respiratory infections with complications. Additionally, there was a reduction in antibiotic treatments for respiratory infection with the intake of a product containing probiotics compared to the control group.
Maintain intestinal microflora balance by displacing or diluting intestinal pathogenic flora: Probiotic microflora reduces the different infections and helps maintain intestinal microflora balance because:
It directly inhibits the pathogenic bacteria in the intestine by competing for nutrients and residing space
It creates an unfriendly low pH environment for pathogenic and putrefactive bacteria by producing organic acids, such as lactic acid, acetic acid, and propionic acid
It produces natural antibiotics, such as acidolin, acidophilin, bulgaricin and plantaricin (bacteriocines) and other substances that inhibit the growth of pathogens.
Decreasing toxic or carcinogenic metabolites and cancer risk: Although direct experimental evidence for cancer suppression in humans resulting from consumption of probiotics is lacking, there is a wealth of indirect evidence based largely on laboratory, in vitro or animal studies. Most of the reported data is on the development of colon cancer using the combination of both probiotics and prebiotics. The reported effects and proposed probiotic mechanism, such as Lactobacillus casei Shirota, on colon cancer development include:
Enhancing natural killer cytotoxicity
CD8 positive T lymphocytes
Binding
Degrading potential carcinogens
Decreasing metabolites of pathogenic or putrefactive bacteria (such as enzymes ß-glucuronidase, nitroreductase and glycocholic acid hydrolase.)
Modulate immune response: Intestinal microflora can have significant influence on immune response in addition to their effects on nonimmunologic gut defense. Probiotic bacteria modulates the host defense mechanisms by affecting both non-specific and modulating gut-associated immune function. Oral administration of different lactic acid producing bacteria such as L. acidophilus and L. casei affect the production of IgA producing cells, enhancing levels of interferon-alpha and polymorphonuclear cell phagocytic capacity. Probiotic bacteria can also suppress inflammatory response and is helpful in controlling intestinal inflammatory diseases. More and more studies show that there is a correlative or suggestive link between immune modulation and enhanced protection by probiotic bacteria. However, not all the probiotic strains have the same immunomodulatory effect.
Alleviating lactose intolerance: The inadequate amounts of the lactose digesting enzyme beta-galactosidase in the intestinal tract can cause diarrhea, abdominal cramping, bloating and other discomforts. This condition is known as “lactose intolerance” or “lactose maldigestion.” The effect of fermented milk and milk products in reducing lactose intolerance are well studied. Fermented milk products, such as yogurt, can improve lactose digestion in lactose maldigesters. This is accomplished by beta-galactosidase secreted by culture bacteria, the delayed gastric empty and slowing intestinal transit. Heat-treated yogurt tends to be less effective than fresh yogurt. In addition, fermented foods with probiotic bacteria tend to be more effective than probiotic supplements alone.
Other health effects: Additional physiological effects of probiotics have been documented or indicated, including the reduction of serum cholesterol, improving bowel regularity, reduction and protection of radiotherapy associated intestinal dysfunction, detoxification, treatment of food allergies, among others. However, more studies are needed before any conclusions can be made.
Safety
Probiotics, especially those belonging to Lactobacillus and Bifidobacterium genera, have a very good safety track record. There have been no reported drug-probiotic interactions. However, not all the species have the same influence on the host, and people with different physiological status or conditions will have various responses to organisms. There have been some isolated incidences in which beneficial bacteria have become infectious. Probiotics should not be recommend to people with compromised immune systems or with conditions prone to infections. People with these conditions should consult their physician before taking probiotic supplements or fermented foods.
Selecting Probiotic Supplements
The viability of probiotic organisms is very sensitive to temperature and moisture. They are usually unstable when non-refrigerated or exposed to moisture. Unless a product is specially manufactured with a systematic control procedure, such as strain selection, fermentation medium and environment, drying, encapsulation and coating, it should be refrigerated. Consumers should question products claiming “no refrigeration needed,” and ask for the documentation from the manufacturer.
Another issue is whether to take a probiotic product with a single strain or mixed strains. Since numerous microorganisms cohabitate in the human intestine and each probiotic strain has its uniqueness, there is a trend toward recommending the supplementation with mixed strains.
The suggested dose of live bacteria is 3 billion to 4 billion daily, but may vary with a person’s physiological conditions. Probiotic products can be found in health/natural food stores and selected supermarkets and drug stores. Probiotics are also available in fermented foods, such as yogurt (especially yogurt with three bacterial strains), acidophilus milk, capsules, tablets, powder and liquid.
Resources for Additional Information
Additional information can be found by searching Pub-Med/Medline online, one of the quickest and easiest ways to get research information about probiotics. Information can also obtained from manufacturers, such as the International Probiotic Association, Canadian manufacturer Institut Rosell and U.S. manufacturer Chr. Hansen Labs.
Peilin Guo, M.S., R.D., is the Vice President of Functional Foods, Clinical Research, and Asian Market Development Research for Jarrow Formulas, headquartered in Los Angeles, CA. She has developed a variety of nutritional and dietary supplements and holds a U.S. patent on a product for improving intestinal health.
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