Probiotics and prebiotics improve management of gut microflora.

We continue to come across indications that probiotics and prebiotics improve our general health. The majority of organisms found in the gut are benign. Some may even be helpful to the body. Bacteria in the colon respond generally to the available fermentable substrate. There is some interest in using our diet to specifically increase the number of health-promoting microbes in the intestine.

Probiotics and prebiotics are two mechanisms by which our health may be improved through fortification of selected bacteria in the gut. Some research has involved using intestinal isolates of bacteria as probiotics. Many species of microorganisms have been used, such as lactic acid bacteria, Bacillus spp. and such fungi as Aspergillus spp.

The positive impact associated with probiotics includes reductions in levels of cholesterol and triglycerides; protection against gastroenteritis; improved lactose tolerance; and stimulation of the immune system. The basis for improved digestibility of lactose in probiotics may involve lactase activity of the bacteria or a stimulation of the host's mucosal lactase activity.

The manner in which probiotics improve colonization resistance in the body may be due to the production of strong acids, other antimicrobial compounds, immune stimulation, the metabolism of toxins or the occupation of potential colonization sites. Studies have shown that probiotic supplementation can affect plasma cholesterol levels.

As you may know, prebiotics are nondigestible ingredients that beneficially affect the body by selectively stimulating the growth or activity of bacteria in the colon that can improve our health. Many potentially health-promoting microorganisms, such as bifidobacteria, already reside in the human colon. To be an effective prebiotic, a colonic food must neither be hydrolyzed nor absorbed in the upper part of the gastrointestinal tract. In addition, it must have a selective fermentation such that the composition of the large intestinal microbiota is altered in a healthier manner.

The prebiotic activity of fructose-containing oligosaccharides has been confirmed. Galactooligosaccharides are also good candidate prebiotics that seem to fulfill most of the associated criteria. Other carbohydrate-based molecules also may be prebiotics, including lactulose, which is used in pharmaceutical products to control constipation and as an additive in infant formula to stimulate lactobacilli.

One future possibility involves the use of biotechnology to improve prebiotic functionality. This may include the development of highly efficacious forms that function at low dosage. Novel oligosacharides may be enzymatically designed.

Further information. Glenn Gibson, The University of Reading, Food Microbial Sciences Unit, Department of Food Science and Technology, PO Box 226, Whiteknights, Reading RG6 6AP, England, U.K.; phone: [phone]; fax: [phone]; email: [e-mail].