In the final part of our gut health series, NutraIngredients.com reviews the science behind the 'friendly bacteria' and the prebiotics fibres that 'fuel' them.

The gut health market is dominated by probiotics and prebiotics. As science continues to expand our understanding of the effects of modulating the intestinal microflora we see that beneficial gut health may only be the tip of the iceberg.

Definitions

According the FAO/WHO, probiotics are defined as "live microorganisms which when administered in adequate amounts confer a health benefit on the host". Prebiotics are "nondigestible substances that provide a beneficial physiological effect on the host by selectively stimulating the favourable growth or activity of a limited number of indigenous bacteria".

Prebiotics are defined as: "A selectively fermented ingredient that allows specific changes, both in the composition and/or activity in the gastrointestinal microflora, that confers benefits upon health wellbeing and health." (2004)

Probiotics

Specific strains of probiotic bacteria exert different effects, and a generalisation of the category would be inaccurate and misleading. The effects of probiotic strains on gut health is well established, and an example of this ever-growing area involved a meta-analysis in The Lancet (2007, Vol. 369, pp. 1614-1620).

Australian reviewers reported that the risk of necrotising enterocolitis, one of the most common gastrointestinal problems in premature babies, may be cut by 74 per cent by probiotic supplementation.

However, in an editorial Parma University's Carlo Caffarelli and Sergio Bernasconi offered a note of caution that is applicable across the probiotic category.

"The analyses were based on clinical trials that tested different probiotics, such as Lactobacillus acidophilus, L casei GG, L bulgaricus, Bifidobacterium bifidum, B breve, B infants, B lactis, Streptococcus thermophilus, and Saccharomyces boulardii. Each strain is believed to have specific immunomodulatory properties," they said.

In terms of boosting immune function, Lactobacillus fermentum was recently reported to boost the immune health of long distance runners, protecting them from respiratory illnesses. The Lactobacillus strain was associated with an enhancement in the activity of T cells, key players in the immune system (Br. J. Sports Med., doi 10.1136/bjsm.2007.044628)

In the human study of its kind, scientists at the Institute of Food Research (IFR) reported that Lactobacillus casei Shirota may modulate the immune response to grass pollen, and help hay fever sufferers (Clin. Exp. Allergy, doi: 10.1111/j.1365-2222.2008.03025.x)

An improvement in the immune function of white blood cells in alcoholics has also been reported by a small study by researchers at University College London. This study also used Lactobacillus casei Shirota supplements (J. Hepatology, doi: 10.1016/j.jhep.2008.02.015)

Another area with considerable research, and yet apparently overlooked because of the nature of the condition, is bacterial vaginosis, a problem that affects about 30 per cent of women between the ages of 14 and 49.

Extensive research by Gregor Reid from the Canadian R&D Centre for Probiotics at the Lawson Health Research Institute, and The University of Western Ontario, led to the conclusion that the combination of two particular strains - GR-1 (Lactobacilli rhamnosus) and RC-14 (Lactobacilli reuteri) - provide the greatest benefit for the relief and prevention of bacterial vaginosis.

Probiotic strains have also been reported to reduce abdominal pain and nausea/vomiting linked to stress (Nutr. Res., Jan. 2008, Vol. 28, pp. 1-5), constipation (Nutr. J., 2007, 6:17 doi:10.1186/1475-2891-6-17), and diarrhoea (British Medical Journal, doi:10.1136/bmj.39231.599815.55).

Prebiotics

The most extensive research to date is with the inulin-type fructans, non-digestible carbohydrates that reach the colon intact and are hydrolysed by specific 'positive' members of the colon microflora.

At 5th Orafti Research Conference in 2006, co-chair of the conference, Professor Allan Walker from Harvard Medical School, told NutraIngredients.com: "Prebiotics potentially may be more relevant [for health] than probiotics."

The reported health benefits of prebiotics relate to improving bones health, reducing the risk of colorectal cancer, boosting immunity, and enhancing satiety and aiding weight management.

In terms of bone health, studies with animals (J. Nutrition, Vol. 132, pp. 3599-3602; Br. J. Nutr., Vol. 88, pp. 365-377) and humans (Am. J. Clin. Nutr., 2005, Vol. 82, pp. 471-476) have shown that inulin/ oligofructose supplementation to a diet results in more absorption of calcium, accumulation of bone mineral and improved trabecular network structure.

Colon cancer is an area that has a growing but already significant number of animal studies linking prebiotic and/or probiotic intake to a risk reduction. The results of the EU-sponsored SynCan project show that the combination of pre- and probiotics (BeneoOrafti's Synergy1 plus Lactobacillus GG and Bifidobacteria) could favourably shift the populations of faecal bacteria, with larger populations of protective bacteria and reduced numbers of cancer-promoting bacteria. (Am. J. Clin. Nutr., 2007, Vol. 85, pp. 488-496).

Despite being early days for the possible benefits in immune health, a number of studies have already been published that show a significant effect of prebiotics in human health. Such an effect is due to impact of non-digestible carbohydrates like inulin and oligofructose on metabolic functions in the intestine, which in turn impact on local immune cells in this area, and particularly on the gut-associated lymphoid-tissue, which plays a role in the immune system. Most of the data in this area comes from rats and mice, however.

As obesity levels continue to rise around the globe, the study of food components for weight management is gaining momentum. Several studies have reported that daily supplement of prebiotic inulin and oligofructose may help in the maintenance of an appropriate body weight and BMI.

Indeed, a study, published in the Journal of Pediatrics (Sept. 2007, Vol. 151, pp. 293-298), reported that the prebiotics supplements of inulin/oligofructose (eight grams, BeneoSynergy1, Orafti) resulted in a much lower increment in BMI over the one year, compared to the control group. Body weight and body fat mass were also significantly lower in the prebiotic group, compared to the controls.

Expanding this area, a breakthrough paper published in Nature in December 2006 reported that microbial populations in the gut are different between obese and lean people, and that when the obese people lost weight their microflora reverted back to that observed in a lean person, suggesting that obesity may have a microbial component.

At a recent scientific symposium organised by the Beneo Group, Dr. Nathalie Delzenne from the Catholic University of Louvain in Belgium and Dr. Robert Welch from the University of Ulster presented results from animal and human studies, respectively, which indicated the potential of prebiotic supplementation to regulated food intake.

IBD and IBS are chronic inflammatory conditions of the intestine that affect about 0.5 per cent of the populations in the Western World, and well-established science has shown that the diseases arise in some people due to a lack of tolerance to gut bacteria. It is no wonder therefore that prebiotics have emerged as an interesting avenue of study for these diseases and conditions. While the application of prebiotics in this area is seen as promising, Glenn Gibson said that the number of studies in this area remains relatively small.