From probiotics to prebiotics and a healthy digestive system

Ingestion of probiotics can be recommended as a preventative approach to maintaining intestinal microflora balance and thereby enhance 'well-being'. Undoubtedly, probiotic bacteria will vary in their efficacy. The literature indicates positive results in over 50 human trials with prevention/treatment of infections the most frequently reported. In theory increased levels of probiotics may induce a 'barrier' influence against common pathogens. Mechanisms of effect are likely to include the excretion of acids (lactate, acetate), competition for nutrients and gut receptor sites, immuno-modulation and the formation of specific antimicrobial agents. An alternative, or additional, approach is the prebiotic concept. This takes the view that probiotics are present indigenous to the gut and that a rational approach towards increasing their numbers would be to consume food ingredients (carbohydrates) that have a selective metabolism in the lower gut. A prebiotic is 'a nondigestible food ingredient that beneficially affects the host by selectively stimulating the growth and/or activity of one or a limited number of bacteria in the colon that can improve the host health.' In particular, the ingestion of fructo-oligosaccharides, galacto-oligosaccharides, and lactulose has shown to stimulate bifidobacteria in the lower gut.

A practical approach to a multi-level analysis with a sparse binary outcome within a large surgical trial

Objectives: To assess the potential source of variation that surgeon may add to patient outcome in a clinical trial of surgical procedures. Methods: Two large (n = 1380) parallel multicentre randomized surgical trials were undertaken to compare laparoscopically assisted hysterectomy with conventional methods of abdominal and vaginal hysterectomy; involving 43 surgeons. The primary end point of the trial was the occurrence of at least one major complication. Patients were nested within surgeons giving the data set a hierarchical structure. A total of 10% of patients had at least one major complication, that is, a sparse binary outcome variable. A linear mixed logistic regression model (with logit link function) was used to model the probability of a major complication, with surgeon fitted as a random effect. Models were fitted using the method of maximum likelihood in SAS((R)). Results: There were many convergence problems. These were resolved using a variety of approaches including; treating all effects as fixed for the initial model building; modelling the variance of a parameter on a logarithmic scale and centring of continuous covariates. The initial model building process indicated no significant 'type of operation' across surgeon interaction effect in either trial, the 'type of operation' term was highly significant in the abdominal trial, and the 'surgeon' term was not significant in either trial. Conclusions: The analysis did not find a surgeon effect but it is difficult to conclude that there was not a difference between surgeons. The statistical test may have lacked sufficient power, the variance estimates were small with large standard errors, indicating that the precision of the variance estimates may be questionable.

The potential therapeutic benefits of consuming 'health-promoting' fermented dairy products: a brief update

Despite the publication of a few contrary indications, the general consensus seems to be that the regular consumption of probiotic cultures, perhaps accompanied by 'prebiotic' compounds, improves the healthy operation of the digestive system of a typical consumer. Whether other benefits follow is a more contentious issue, especially for a given individual. Nevertheless, the dairy industry needs to be aware of the various ideas that are currently being explored, and this brief review seeks to summarize some recent findings.