Frequency of constipation has been linked with poor mood, possibly because of gastric discomfort and bloating. Probiotics – live beneficial bacteria added to food or drinks – are
known to relieve constipation. British researchers brought these two aspects together in order to test the impact of a probiotic drink on mood and bowel habits.

124 healthy subjects were recruited into the study and asked to take a daily probiotic drink or a dummy (placebo) product for 3 weeks. During this time, mood and psychological tests were
carried out. Diaries of bowel habit were also kept. The study was double-blind, meaning that neither the subjects nor researchers knew which person was receiving which type of drink.

Before the study began, subjects who rarely experienced constipation were more likely to describe their mood as clear-headed, elated and confident. At the end of the study, no significant
changes in mood across the whole sample were seen, and there were no changes in the reported frequency of bowel movements. This contradicts other studies which have found improvements in bowel
habits following regular consumption of probiotic drinks. However, in this study, the lack of result may have been influenced by the relatively low incidence of constipation at baseline.

When subjects were divided into ‘good mood’ and ‘poor mood’ groups based upon their initial tests, consuming probiotics for 3 weeks did appear to increase feelings of
happiness in subjects from the ‘poor mood’ group.

The authors concluded that the probiotic-containing yoghurt drink improved mood in subjects whose mood was initially poor, but had no impact on bowel habits.

For more information see
Benton D et al (2007). Impact of consuming a milk drink containing a probiotic on mood and cognition. European Journal of Clinical Nutrition, vol 61: pp 355-361.