Probiotics and Prebiotics - Their Use for Good Health

By James Collier, Nutrition Consultant

Bacteria colonise all external surfaces of the human body, one of the most favourable areas being the large intestine, where there is a large surface area, an abundant source of nutrition, a stable pH and stasis to favour fermentation. Hence certain strains flourish in this environment. Humans have evolved a symbiotic relationship with the normal bacterial flora; humans provide conditions for the bacteria to flourish and the bacteria help break down otherwise indigestible nutrients. The bacteria also assist in preventing gut infection, providing essential nutrients for colonocytes and aid detoxification of minor plant components (Hill 2002).

Foods containing probiotics and/or prebiotics are functional foods, which are any foods which, on top of their nutritional value per se, have been developed through research to have a function in good health.

What are Probiotics?
Probiotics are live strains of 'good' bacteria, which help our digestive system work efficiently, e.g. bifidus, lactobacillus and acidopilus. Schrezenmeier & De Vrese (2001) define a prebiotic as: 'A preparation or product containing viable, defined microorganisms in sufficient numbers, which alter the microflora of the host intestine and, by that, exert beneficial health effects on the host'.

They are found in live yoghurts, powders or specially formulated probiotic drinks which contain one or more of the strains of these 'good' bacteria. With food processing, pollution and antibiotic therapy, numbers of 'good' bacteria occurring naturally in our gut are reduced, and research has shown, by actively consuming the bacteria, the size of the colonies in the gut can be increased, which improves digestion. Moreover, the numerous studies have also shown that with optimal numbers of 'good' bacteria, the immune system is improved, increasing our ability to fight disease. Probiotics may also have a role in reducing the severity of allergies.

What are Prebiotics?
A prebiotic is a nutrient which specifically stimulates the growth of the naturally occurring microorganisms in the digestive tract, specifically Lactobacilli or Bifidobacteria. Examples are inulin, other fructo-oligosaccharides (FOS) and other soluble fibres found in pulses, fruit and some cereal products. These nutrients require a specific fructosidase enzyme to make them available for fermentation, which is only produced by bifidobacteria and some lactobacilli, thus these organisms are specifically stimulated.

Thus prebiotics exert the positive effects of probiotics, including helping digestion and the immune system, and, as they stimulate the growth of strains already present, they ensure the health benefits of the normal flora will be enhanced. This sounds very favourable, but much less work has been done on prebiotics than on probiotics.

The effect of a probiotic may be enhanced by having a prebiotic in the support medium; for example milk contains nutrients for lactic acid bacteria, and so many probiotics are milk-based.

What are the benefits of probiotics and prebiotics?
The main aim of both probiotics and prebiotics is to increase the colony size and resistance of the gut's natural flora, and more and more people are including them in their diet to promote good health. The results of this include a healthier digestive and possibly reduced incidence or severity of irritable bowel syndrome. Pro- and prebiotics also modify the immune function of the gut to help its ability to combat pathogenic bacteria. The list below lists claimed benefits of pro- and prebiotics:

  1. Gastro-intestinal
    • Help prevent infant and adult enteritis
    • Prevention of diarrhoea
    • Reduce severity of intestinal disease, possible benefits in inflammatory bowel diseases
    • Treatment of antibiotic associated diarrhoea
    • Reduce the need for antibiotic therapy
    • May help symptoms of irritable bowel syndrome
    • Improved lactose digestion in lactose sensitive individuals
    • Reduce risk of food poisoning
  2. Immune system
    • Modulate cytokine production
    • Modulate cell proliferation
    • Modulate macrophage activity
    • Enhancement of non-specific immune defence systems
    • Reduce severity of hypersensitivity
  3. Anti-carcinogens
    • Degrade nitrosamine compounds
    • Bind heterocyclic amines produced by pyrolysis of meat
    • Decreases levels of faecal enzymes involved in carcinogen activation
  4. Serum lipids
    Very large doses have indicated reduced total serum cholesterol
  5. Production of vitamins
    Production of additional B-vitamins
  6. General
    • Improved general health and well being
    • Reduced incidence of illness
    • Improved digestion and absorption of nutrients
    • Improved sports performance due to better health and digestive function

There have been studies demonstrating success in treatment of gut bacterial infections, in particular in treating antibiotic associated diarrhoea (Gorbach et al 1987). Most studies which have looked at the immunomodulating effects or probiotics have looked at non-specific immunity, including looking at macrophage and cytokine activity (Schiffrin et al 1997).

Fermented milk products containing probiotic strains have also been shown to modulate the ability to tolerate milk in lactose sensitive individuals. Increased probiotic strains in the gut are also potent producers of B-vitamins, thus more are available in the bowel for absorption. Other suggested health benefits include possible reduction in serum total cholesterol level and acting as anti-mutagens and anti-carcinogens. Unfortunately, these studies have merely been in vitro, though early reports of improved levels of certain beneficial enzymes have been indicated (Hill 2002).

All beneficial probiotics are lactic acid bacteria, for important reasons. Firstly, they are safe, and are not causal of food poisoning. They can also influence colonisation resistance, shown by animal and in vitro studies (Drasar & Roberts 1990). If Lactobacillus spp and Bifidobacterium spp are present in the colon in sufficient numbers to significantly augment those already present, they could protect from food poisoning, shown in vitro with Salmonella spp and Shigella spp. Also, although Clostridium spp are rapid growers in the gut, high levels of Lactobacillus and Bifidobacterium spp can suppress their growth and dilute their numbers. This could have significant clinical benefits, but further evidence is required.

Should we use probiotics and prebiotics?
The use of pro- and prebiotics to maintain healthy gut bacterial flora is increasing due to increasingly good evidence of their benefits to health and from marketing by manufacturers. However, there remains huge deficiencies in our understanding of these functional foods, and much more research is required to demonstrate benefits to clinical outcome and reduction in costs in the hospital setting. Benefits to health in general are apparent and consumption of probiotics from live yoghurts, special powders or probiotic drinks is increasing. More recently, live bacteria and FOS are being further added to nutritional supplement formulas and nutraceuticals. There is also significant interest in probiotics and prebiotics from the sports supplement industry.


Drasar BS, Roberts KA (1990). Control of the large bowel microflora. In Human Mircobiol Ecology (Ed Hill MJ, Marsh PD). CRC Press, Boca Raton pp87-110
Gorbach SL, Chang T, Goldin B (1987). Successful treatment of relapsing Clostridium difficile colitis with Lactobacillus GG. Lancet ii, 1519
Hill M (2002). Probiotics, prebiotics and health. Functional Nutrition 1(1) 5-8
Schrezenmeier J, De Vrese M (2001). Probiotics, prebiotics and synbiotics – approaching a definition. Am J Clin Nutr 73 (Suppl) 361s-364s
Schiffrin EJ, et al (1997). Immune modulation of blood leucocytes in humans by lactic acid bacteria: criteria for strain selection. Am J Clin Nutr 66(Suppl) 15s-20s