The scientists reviewed research that had looked at the ability of bacteria from dairy products such as yoghurt, fermented with probiotic bacterial cultures, to reduce the unpleasant symptoms associated with gastrointestinal conditions like lactose intolerance, constipation, diarrhoeal diseases, colon cancer, inflammatory bowel disease and food allergies.
While they did not conclude that the reported results were incorrect or misleading, they found inconsistencies which they attributed to differences in the strains of bacteria used, the routes of administration, or a lack of an objective definition of 'gut health'.
Probiotics are based on the notion that there is such a thing as a normal healthy microflora. However, the Boston team led by Osker Adolfsson, noted that: "normal healthy microflora had not been defined except perhaps as a microflora without a pathogenic bacterial overgrowth."
The group therefore advocated further studies to substantiate past findings either through animal models and clinical trials. They were specifically interested in ascertaining whether beneficial effects were age-specific and to investigate the mechanisms through which yoghurt works.
It would also be of particular interest to the burgeoing functional food industry, which markets probiotics as improving 'gut health', for scientists to discover what really are the defining characteristics of a healthy gut.
This research is published in the American Journal of Clinical Nutrition (Vol. 80 (2), 2004).
Meanwhile, IA Abd El-Gawad and colleagues from Cairo University, Egypt, reported this week in the British Journal of Nutrition, Vol. 92 (1), 2004, that probiotic yoghurt and soya yoghurt significantly prolonged the lives of mice with tumours.
The scientists found that the mice fed with yoghurt containing bifidobacterium lactis Bb-12 or B. longum Bb-46 out lived those fed products without the probiotic bifidobacteria.
Probiotics is one of the fastest growing functional food markets worldwide. Europe's probiotics market is set to more than triple in value over the next six years, according to Frost & Sullivan, to reach $137.9 million (€118.5m) in 2010.
A recent study of the UK market by KeyNote found that it grew by 10.8 per cent in value terms for the 12-month period ending October 2003, after a substantial 24.7 per cent growth in the previous year to October 2002 - still well above the growth of equivalent traditional products.
KeyNote suggested this growth was thanks to significant education campaigns, designed to teach the concept of 'good bacteria'.