Many bacteria flourish in the digestive tract, including Lactobacillus and Bifidobacterium varieties. The maintenance of healthy intestinal flora aids digestion and boosts the immune system. Claims have also been made that good intestinal function may reduce the risk of colorectal cancer.
Probiotics (literally “pro life” or “for life”) are dietary supplements which contain potentially beneficial bacteria and yeasts. The rationale behind them is that antibiotics, stress, illness and a variety of other causes reduce the number of intestinal flora in the digestive tract. Danone claimed that weather changes may have be among them on the now-defunct UK Actimel site.
Probiotic products aim to deliver extra intestinal flora to the gut to aid with digestion, which may engender temporary colonies of bacteria that assist the body’s natural flora. However, if the conditions which lead to the depletion of the intestinal flora persist, their benefits will be short-lived, which may be why Danone recommends that its probiotic yoghurt Activia is eaten at least once a day.
A healthy level of intestinal flora can also easily be ensured by maintaining a diet with a good level of prebiotics, which occur in such foods as raw oats, unrefined wheat, artichokes and chicory. The benefits of a single kind of bacteria being added to the gut are also brought into question by the fact that there are millions of different kinds of bacteria in the gut already. The Activia site for the USA used to provide a PDF Scientific Summary For Health Care Professionals which has since been taken down. Danon are specifically targeting healthcare professionals to ask them to prescribe Activia.
There is emerging evidence that probiotics may help elderly patients recover from surgery quicker by countering some effects of antibiotics, but there is also evidence that probiotics can be dangerous for patients with acute pancreatitis : Probiotics may be useful in some medical settings, and may be extremely harmful in others
The BBC has recorded an excellent radio programme about gut bacteria, including a discussion of the fundamental uncertainty about the very specific advertised claims for probiotics.