Probiotics are supplements containing bacteria. Probiotics have been found to be good for certain conditions (such as antibiotic-induced diarrhea), but woo-meisters frequently make extravagant and unsubstantiated claims about their being able to "boost the immune system" and "replenish the gut flora", and the like.
Since probiotics, like many other nutritional supplements, are practically unregulated, the actual contents of the pills can differ substantially from what's on the label. One study has shown that probiotics often contain bacteria not listed on the label and do not contain species that are listed on the label.
In a nutshell
- Probiotics, Mark Crislip, Science-Based Medicine.
- Rapid determination of the bacterial composition of commercial probiotic products by terminal restriction fragment length polymorphism analysis, J Pediatr Gastroenterol Nutr. 2008 May;46(5):608-11. doi: 10.1097/MPG.0b013e3181660694.