Trillions of bacteria naturally occur in the intestines, and most help protect the body from disease. These protective bacteria are called probiotics. Foods that nourish these "good" bacteria are termed prebiotics. A number of factors can upset the balance between the levels of "good" and "bad" bacteria. There is evidence that consuming foods that are rich in "good" bacteria and foods that nourish these bacteria may help maintain a healthy balance of bacteria in the body and help improve certain disease conditions.
The body has four lines of defense against infection: skin, mucosal lining, immune system, and gut microflora, sometimes referred to as gut microbiota. Research has shown that adding "friendly" bacteria to the diet will improve the health of gut microflora and may help protect both the lining of the intestinal tract and the immune system. Probiotics are defined as live microbial food ingredients that have a beneficial effect on human health, when ingested live and in sufficient numbers. It is now common practice to add probiotics, similar to bacteria already present in the body, to fermented foods such as yogurt.
Knowledge of the health benefits of probiotics can be traced back many years when a Nobel Prizewinning scientist and director of the Pasteur Institute, Elie Metchnikoff, hypothesized that Bulgarian peasants owed their health and longevity to the consumption of fermented milk products containing lactobacillus, a probiotic bacterium. By 1997, the use of probiotics was becoming well established in Europe, with fermented dairy products accounting for 65% of the European "functional food" market. Health conscious Americans are the fastest-growing segment of consumers of probiotic foods.
Different Types of Probiotics
The two most common bacteria added in the production of probiotic foods are lactobacilli and bifidobacteria. There are numerous species of lactobacilli and bifidobacteria; the main species thought to have probiotic characteristics are L casei, B lactis, L johnsonii, B breve, L bulgaricus, B animalis, L rhamnosus, B infantis, L reuteri, B longum, and L acidophilus.
Today there are more than 70 lactic acid bacteriacontaining products worldwide, including sour cream, buttermilk, yogurt, powdered milk, and frozen desserts. More than 53 different types of probiotic milk products are marketed in Japan alone. Probiotics have traditionally been consumed as fermented dairy products such as yogurt. They have also recently been incorporated into drinks and, in the future, may be found in fermented vegetables and meats. They are also being marketed as dietary supplements in tablet, capsule, and freeze-dried preparations.
Health Effects of Probiotics
The health of the gut largely relies on the balance between good and bad bacteria, and probiotics may help the gut prevent an imbalance in which there are too many harmful bacteria. Most of the research on probiotics has been conducted through small clinical studies or epidemiological studies. This research has shown that probiotics may be promising as treatments for a number of diseases and conditions, including lactose intolerance, diarrhea secondary to antibiotic use or E coli infections, other gastrointestinal infections, vaginal candidiasis infections, and lactose malabsorption due to chemotherapy. Research has reasonably well established that probiotics improve the body's ability to resist intestinal infection and improve digestion. Only limited evidence, however, suggests that probiotics have cholesterol-lowering benefits, reduce the risk of cancer, produce vitamins, or reduce the risk of urogenital infections other than Candida. Although there is relatively little harm in taking probiotics, more research is necessary to establish a firm basis for using probiotics for specific health benefits.
Prebiotics: The Companion Nutrient
Gut microflora need an environment in which to thrive. Dennis T. Gordon, PhD, Professor and Chair of the Department of Cereal Science at North Dakota State University, explains, "Fermentable dietary fiber is a source of prebiotics and the necessary energy source for our intestinal microbiota." According to an article titled Protective Nutrients and Functional Foods for the Gastrointestinal Tract in the American Journal of Clinical Nutrition (75:789-808), by Christopher Duggan et al of Children's Hospital, Boston, inulin and oligofructose are the two most commonly studied prebiotics. Both inulin and oligofructose are found naturally in many fruits and vegetables as well as in whole-grain foods. They are also widely used commercially to add fiber to foods without adding bulk.
Health Effects of Prebiotics: Most of the research on the potential health benefits of prebiotics has been done in animal or in vitro studies. Studies of inulin have shown that it may have a promising role to play in providing relief from constipation and suppressing diarrhea. Some studies also suggest a possible benefit for reduced risk of osteoporosis through increased calcium absorption, reduced risk of atherosclerosis through decreased cholesterol and triglycerides, and improved insulin response, thus leading to reduced obesity and possibly type 2 diabetes.
Consuming Prebiotics and Probiotics
Prebiotics and probiotics are safe to eat and have many positive health benefits. Eating a combination of prebotic and probiotic foods (or symbiotic foods, those that contain both prebiotics and probiotics) may provide the most health benefits. Prebiotic and probiotic products are now widely available. Manufacturers formulate their products with different types and amounts of probiotic bacteria. Most work best when refrigerated or vacuum-packed to preserve the freshness of the bacteria.
Currently, there are no established recommended consumption levels of prebiotics and probiotics for beneficial effects. More research is needed to determine who will benefit most from consumption of those foods and who should potentially avoid them. Nutrition scientists also recommend that immunocompromised individuals (eg, the young, the elderly, or patients with AIDS, Crohn's disease, or enteric infection) should check with their doctor before consuming probiotics and prebiotics. As always, it is important that individuals not self-diagnose any health condition but speak to their health care professionals for advice on the nutritional component of any treatment plan.
The Future of Probiotics and Prebiotics
Dr. Gordon sums up the current state of the science by saying, "Probiotics are helping us to not only understand but also improve intestinal health. Emerging research is also revealing an important supporting role for prebiotics." The determination of specific strains of beneficial bacteria may help address various gastrointestinal diseases including Crohn's disease and ulcerative colitis, irritable bowel syndrome, and infections in the stomach and small intestine. Research may also find ways for probiotics to improve tube feedings and infant formula as well as improve the nutritional health of the elderly.
This article is adapted from Food Insight, published by the International Food Information Council, Washington, DC.