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For other articles and previous issues click here. August 1, 2005 Living
Bacteria — The Body’s Natural Defense It’s alive! And evidence is mounting that probiotics can play a more therapeutic role in gut health. At the microscopic level, the human body is colonized by millions of bacteria all jockeying for position—some intent on fostering disease and others inherently fending off diseases by improving health and wellness. The probiotic concept suggests that adding certain bacteria to our diets can encourage the beneficial microbial activities in our bodies. The Food and Agriculture Organization defines probiotics as “live microorganisms which when administered in adequate amounts confer a health benefit on the host.”1 Numbers and bacterial population types vary among the stomach, small intestine, and colon because different transit times and secretions affect numbers and composition of microflora. The most heavily colonized area of the human body, the large intestine, has been found to have the highest degree of metabolic activity.2 At birth, the large gut microflora is being established and teeming with strains such as Escherichia coli (E. coli). From infancy, diet plays a major role in determining development of types of bacterial species. Breast-fed vs. formula-fed infants show a marked difference in the predominant microflora. The fecal flora of breast-fed infants is so heavily dominated by the probiotic genus, Bifidobacterium, that it is considered the “gold standard” type of gut flora, which imparts excellent resistance to infection.2 On the other hand, in formula-fed infants, no one microbial group predominates—rendering the system less able to fight infection. In the human adult colon, research has shown that bacteria play a huge role in health maintenance. The adult colon is approximately 150 centimeters in length with a typical transit time of 24 to 72 hours—enough time for large numbers of bacteria to grow.3 The colon is a breeding ground for bacteria with roughly 100 grams of dietary residues from carbohydrates, proteins, amino acids, and lipids entering it daily. Thus, ample growth substrate is present for nourishing native colonic bacteria sources, such as mucus secretions and epithelial cells. Ninety percent to 95% of total cells in the body are thought to be large intestinal bacteria.3 It makes sense that gut bacteria affects health and disease as much as it does. According to Glenn Gibson, PhD, professor of food microbiology at The University of Reading, United Kingdom, “Probiotics prophylactically manage acute and chronic gut disorder; evidence is accumulating for a more therapeutic role, also. Higher levels of these beneficial organisms can thereby reduce the activities of more problematic pathogens—either present in the gut or transmitted in food and/or water.” Disease Proliferation and Health
Maintenance Consumption of specific strains of probiotics is associated with a range of health benefits, such as improvement of diarrheal conditions (acute infantile diarrhea, antibiotic-associated diarrhea, nosocomial infections), lactose intolerance, systemic infections, allergies, cancer, hypercholesterolemia, inflammatory bowel disease, and immunomodulation.4,5 Probiotics and Prebiotics In other words, says Gibson, “a prebiotic is a dietary ingredient that enters the gut and fortifies components of the indigenous flora seen as beneficial.” Global Historical Perspective The awareness and acceptance of beneficial bacteria differs globally. The U.S. thinking is less progressive in this area. “There is little understanding of ‘good’ cultures as we are more focused on bacteria as a pathogen,” says Mary Ellen Sanders, PhD, president of the International Scientific Association for Probiotics and Prebiotics. Asia and the European Union throw big money at research in the probiotics/prebiotics arena. “Europeans like fermented dairy products as reflected in higher consumption in Northern Europe; Asian people don’t mind talking about bowel health as they are much more intestinal and GI [gastrointestinal] health-oriented,” she explains. Active Cultures Some yogurt manufacturers disclose the exact strain of bacteria used in the product, but most do not. As Sanders points out, “most dairy products containing probiotics in the U.S. do not provide information to consumers on product- or strain-specific efficacy research, dose, or even strains used in the product.” Sanders is a big proponent of manufacturers providing information about the specific bacterial strains used. “Different strains of even the same species of bacteria may have different functions. Think of how different a Chihuahua and German Shepherd are even though they are of the same species,” she says. Approximately 80% of the yogurt manufactured in the United States contains Lactobacillus acidophilus added as a probiotic.7 Bifidobacterium strains are also added to some yogurts. The National Yogurt Association established a “Live Active Culture” seal that can be used on the label of any yogurt containing 108 viable lactic acid bacteria per gram at the time of manufacture. However, this seal does not tell the consumer anything about the level of probiotic bacteria added in addition to the yogurt starter cultures.7 Other dairy products that contain probiotic bacteria are culture-added fluid milks (eg, Sweet Acidophilus milk), some cottage cheeses, a few cheeses, and some nondairy milk-type beverages. Outside the United States, probiotic-containing food products include cheese, toddler formula, and juices.7 The FDA is open to allowing Streptococcus thermophilus and Bifidobacterium lactis in infant formula for those aged older than 4 months, but no such products are yet on the market in the United States. Functional Foods The role functional foods may play in enhancing human health is continuing to develop.8 There is currently no legal definition of functional food in the United States; however, it is frequently defined as foods that offer health benefits beyond basic nutrition.8 Embedded in any discussion of diet and health is the concept of functional foods; however, the question of optimal health is complicated by matters such as food composition patterns, food synergy, interactions among food components, and the impact of sustaining dietary patterns over the long term.8 Probiotics are widely recognized as functional ingredients for both food enhancement qualities and/or as a basis for dietary supplements. “I am more inclined to recommend functional foods containing probiotics than supplements. The advantage of food sources of probiotics is that they supply a combination of other nutrients besides probiotics and may also help ensure the survival of the probiotics in the intestinal tract,” explains Jeannie Moloo, PhD, RD, a registered dietitian in private practice in Roseville, Calif., and spokesperson for the American Dietetic Association. The lactic acid-excreting bacteria, such as lactobacilli (eg, L. casei, L. acidophilus, L. fermentum, L. johnsonii, L. plantarum, L. rhamnosus) or bifidobacteria (eg, B. longum, B. infantis, B. bifidum) are the most widely used in functional foods and supplements. Lactococci, streptococci, and yeasts such as Saccharomyces are also used in probiotic products. “Probiotics differ in their ability to resist gastric acid and bile acids and colonize in the intestinal tract,” emphasizes Moloo. Regulation of Probiotics and
Prebiotics Global efforts on the part of national regulatory agencies have improved with respect to ensuring that product claims are truthful and not misleading. The science of determining predictors for efficacy on human health is plagued with barriers. One large barrier to the development of biomarkers relevant to the study of probiotics is that the composition of the human gut flora is not fully characterized and the significance of the presence, absence, or certain levels of different genera, species, or strains of bacteria is not understood.9 Efficacy Evidence • In vitro evidence has been found to be a good first step in screening for probiotic safety and efficacy; these studies are useful for providing important strain characterization data. However, they have been found to be too simplistic and fail to successfully mimic the conditions in the human organism. • Animal model systems are important in gaining approval for human studies by institutional review boards, as only limited tests can be preformed in humans for ethical reasons. The weakness of this mode of evidence gathering is that there are anatomical, metabolic, and physiological differences between animals and humans. They work as indicators of efficacy, but usually the doses used in animal studies are not realistic for humans. • Human case studies are very general as they only take into account a single case. Results are likely to be biased toward specific cases and do not provide sufficient evidence of probiotic or prebiotic efficacy. They can raise public awareness but should always be confirmed by well-designed, randomized, double-blind, controlled trials. • Well-designed, randomized, double-blind, controlled human trials are the most effective ways to evaluate functional foods. The trick is defining the active ingredients of a product as it is sold in the marketplace because with time and storage conditions, the product may undergo changes. The other considerations are developing an appropriate placebo, adequately randomizing the study, and being able to reproduce the study at different sites. Long-term intervention studies are needed to observe the improvement of wellness. Most probiotic and prebiotic studies are short-term (less than 12-week) studies.9 Education “We need to keep in mind that most clinical studies have been small, making it difficult to draw conclusions regarding the efficacy of probiotics,” cautions Moloo. “Not all probiotics are alike and as a result, clinical benefits will differ among people. Probiotics differ in their ability to resist gastric acid and bile acids and colonize in the intestinal tract. What we know to date is that there are three general methods by which intestinal microflora can be altered: by taking antibiotics, prebiotics, or probiotics.” Adequate Dosing for Health Benefits “To me, there is no upper dose. Since the gut is so hugely competitive and there are millions of bacteria there already, the more the better as far as probiotics go,” advises Gibson. As far as prebiotics, the dosage ranges from 5 to 15 grams per day, with 8 grams per day on average. Future of Beneficial Bacteria
Experts contend that the future of probiotics warrants more research to confirm physiological benefits, identify mechanisms of action, and develop the technology to improve delivery of products that are attractive to the consumer. — Victoria Shanta-Retelny, RD, LD, is a practicing dietitian at Northwestern Memorial Wellness Institute in Chicago, a freelance food and nutrition writer, and a culinary spokesperson. References 2. Gibson GR. Bacteria for dinner: The rise of probiotics. School of Food Biosciences, The University of Reading, UK. 3. Gibson GR, Rastall RA. Which bacteria should we be feeding when we eat dinner: How and why? School of Food Biosciences, The University of Reading, UK. 4. Gill HS, Guarner F. Probiotics and human health: A clinical perspective. Postgrad Med J. 2004;80:516-526. 5. Teitelbaum JE, Walker WA. Nutritional impact of pre- and probiotics as protective gastrointestinal organisms. Annu Rev Nutr. 2002;22:107-138. 6. Gibson GR, Fuller R. Aspects of in vitro and in vivo research approaches directed toward identifying probiotics and prebiotics for human use. Journal of Nutrition. 2000;130:391S-395S. 7. Sanders ME. Probiotics: Considerations for human health. Nutr Rev. 2003;3(61):91-99. 8. Sander ME, Heimbach JT. Functional foods in the USA: Emphasis on probiotic foods. Food and Science Technology Bulletin. 2004;8:1-10. 9. Sanders ME, et al. Weight of evidence needed to substantiate a health effect for probiotics and prebiotics. Eur J Nutr. 2004;1-8. 10. Reid G, Sanders ME, Gaskins HR, et al. New scientific paradigms for probiotics and prebiotics. J Clin Gastroenterol. 2003;37(2):105-118.
— Source: Gibson GR. Bacteria for dinner: The rise of probiotics. School of Food Biosciences, The University of Reading, UK.
— Source: Gill HS, Guarner F. Probiotics and human health: A clinical perspective. Postgrad Med J. 2004;80:517.
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