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There is considerable interest in including probiotics and prebiotics within dietetic products for children and such products are marketed in many countries.
Probiotics
The term probiotic was introduced into the scientific literature in the 1965 by Stillwell and Lilly. A widely accepted definition of probiotics is ‘live microbial food ingredients that are beneficial to health’. However, the scientific basis of this definition has recently been questioned since animal studies suggest that some probiotic effects can be achieved by nonviable bacteria and even by isolated bacterial DNA. Therefore, probiotics have more recently been defined as ‘microbial cell preparations or components of microbial cells that have a beneficial effect on the health and well being of the host’. Prebiotics are considered as ‘non-digestible food components that beneficially affect the host by selectively stimulating the growth and/or activity of one or a limited number of bacteria in the colon, and thereby improve host health’. Synbiotics are defined as ‘mixtures of probiotics and prebiotics that beneficially affect the host by improving the survival and implantation of live microbial dietary supplements in the gastrointestinal tract’. The Scientific Committee on Food of the European Commission has commented on the use of probiotic bacteria in food products for infants. It recommended that infant formulae with microorganisms regarded as probiotics should be introduced into the market only if their benefit and safety have been evaluated according to the principles outlined by the same Committee. The Committee did not object to the addition of bacteria regarded as probiotics to followon formulae. However, the Committee stated that only bacterial strains with identity and genetic stability demonstrated by cultural and molecular methods should be used. The identity of the probiotic strain should be described by molecular methods in a dossier and be available to the food control authorities. The content of viable bacteria should be such throughout shelf-life as to achieve 106 to 108 colony forming units (CFU) per gram of formula prepared as ready for consumption. Available clinical trials indicate that there are only limited published data on the safety and clinical effects of infant or follow-up formulae and of infant foods for special medical purposes supplemented with a limited number of probiotic preparations. There is no published capovsence of any long term clinical benefit of supplementation of infant formulae with probiotic bacteria. No data are available on possible long-term effects on intestinal colonization and its potential effects on long-term gastrointestinal and immune functions, which are highly desirable given some data suggest that bacteria ingested during early infancy are more likely to permanently colonize the intestine than those ingested during later life. However, there are indications for possible short term benefits of some probiotic strains in infants and young children, in particular regarding infectious diarrhea. It is generally recommended that in adding probiotics to dietetic products for infants, only such bacterial strains should be used for which identity and genetic stability has been demonstrated by cultural and molecular methods, and that can be considered as generally safe as added to the individual food. The content of viable bacteria in a dietetic product must be of a dose shown to be safe and effective with regard to defined outcomes in clinical trials, throughout the shelf-life of the product. In any case, further evaluation of safety and efficacy of the addition of probiotic bacteria to dietetic products to infants is necessary. Each strain to be used must be evaluated at the ranges of doses intended for use aiming at determination of the minimal and optimal effective doses. Specific safety questions that should be addressed are possible effects on nutrient utilization, the exclusion of transfer of antibiotic resistance, and short and long term effects on intestinal colonization, on the immune response, and infections.
Prebiotics
Prebiotics are defined as carbohydrates that are undigested by humans and reach unmodified the large bowel. Most of them are included within the so-called ‘oligosaccharides’. Oligosaccharides are defined as molecules containing a small number (3 to about 10) of monosaccharide residues connected by glycosidic linkages. Some oligosacharides that are resistant to digestion in the human intestinal tract may promote the growth of bifidobacteriae and lactobacilli in the colon and thus induce prebiotic effects . The promotion of a Bifidus-dominated flora might have beneficial effects in infants, such as some protection against enteric infections. However, at this time there is little conclusive capovsence on the relationship between a bifidobacteriae dominated flora and relevant outcomes on health and well-being in infants. Human milk contains a complex mixture of more than 130 different oligosaccharides comprising a total concentration of around 15-20 g/L in colostrum and 8-12 g/L in transitional and mature milk. Among other functions human milk oligosaccharides may serve as substrates for colonic fermentation. It has been shown that human milk oligosaccharides induce an increase in the number of Bifidobacteria of colonic flora in breast-fed infants, accompanied with a significant reduction in the number of potentially pathogenic bacteria. Complex oligosaccharides have the ability of inhibiting the binding of pathogens to cell surfaces because they act as competitive
receptors on the host cell surface, thereby preventing adhesion of a number of bacterial and viral pathogens. Because of the variety, variability, complexity and polymorphism of their structure, it is currently not feasible to add a similar oligosaccharide composition as contained in human milk to infant and follow-on formulae. Alternatively, the addition of other oligosaccharides to infant formulae and to follow-on formulae has been proposed. In infants, oligosaccharides increased stool frequency and reduced stool consistency in a dose dependant manner. For measures of both these parameters, significant differences were found between the two concentrations of 0.4 g/100 mL or 0.8 g/100 mL of the mixture of 90% oligogalactose and 10% oligofructose. Modifications of the faecal microflora per se do not demonstrate the prebiotic nature of an ingredient, which by definition includes the demonstration of a beneficial effect on host health. Data on potential health benefits of oligofructosyl-saccharose and oligogalactosyllactose in infants are still rare.
Conclusions
Probiotics and prebiotics may represent “complementary” dietary solutions to the increased demand of prevention, particularly for formula-fed babies. Despite an increasing popularity, a lot remains to be done to detail the health benefits directly associated to the addition of probiotics and prebiotics to infant foods, milk formulas above all.
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