There is now fair evidence to suggest that probiotics reduce certain constipation-related symptoms.
A new study looked at a specific strain of probiotics: Lactobacillus casei as a treatment for functional constipation in otherwise-healthy subject. There was a small but significant improvement in constipation severity at week 4 – this was seen to grow over time.
For some reason the authors used a milk drink containing a mix of sugar, skimmed milk powder, glucose, calcium, vitamins, and permitted flavourings. This would not have been especially useful in patients with lactose intolerance – interestingly, they did exclude patients with milk protein allergy.
However, some studies show that multi-strain probiotics have greater efficacy than single strains, including strains that are components of the mixtures themselves – so it might have been better for the authors to do a multi-strain probiotic. It may also have been useful to compare the result with a probiotic capsule that would have not contained the sugar and glucose and skimmed milk powder that the drink contained.
The Study: Journal of Gastroenterology and Hepatology. Effects of a Probiotic Fermented Milk on Functional Constipation: A Randomized, Double-blind, Placebo-Controlled Study.Mena Mustapha Mazlyn, Lee Hun-Leong Nagarajahl Arshad Fatimah, A Karim Norimah, Khean-Lee Goh. J Gastroenterol Hepatol. 2013;28(7):1141-1147.
other refs: European Journal of Nutrition. Health benefits of probiotics: are mixtures more effective than single strains?
C. M. C. Chapman, G. R. Gibson, I. Rowland February 2011, Volume 50, Issue 1, pp 1-17