Probiotics are living bacteria or other microorganisms that have beneficial health effects in people when they’re ingested. Probiotics have become very popular and many of my patients are taking probiotics to gain some health advantage, but enthusiasm for a concept is not the same as scientific proof of effectiveness.
Here’s the truth: Very few marketed probiotics have had their health benefits investigated scientifically and of the ones that have been studied, the reasons that they are of benefit are obscure. Here’s what you need to know if you’re thinking about starting probiotics.
What makes a healthy gut microbiome?
Studies in animals (where conditions can be manipulated experimentally) show that changes in the gut microbiome can have profound effects on body function and susceptibility to disease. Studies in humans suggest that the microbiome may be important in training our immune system, metabolizing what we eat and affecting how our body works.
In addition, the microbiome may have a role in the development of metabolic diseases, such as obesity or diabetes, and in the defense against gut infections, such as colitis due to Clostridium difficile. It may play an important role in inflammatory bowel diseases, like Crohn’s disease, and irritable bowel syndrome.
These conditions—and others—have been associated with a decrease in the diversity of the microbiome, but it is important to realize that association is not the same as causation. It may be that it is the entire ecosystem that determines the impact of the microbiome on our health rather than the presence or absence of any one specific organism.
Most probiotics lack research to back health claims
The idea that the billions of germs living in our intestines do us some good is a great concept, but proof that ingestion of specific probiotic strains has any health benefit is lacking for most conditions. Most of the studies that have been published are small studies in small groups of patients, and they are not necessarily conclusive.
Relatively few strains have been studied in any detailed way, and most seem to have limited effectiveness in managing specific disorders. Problems that have been said to benefit from probiotics include infectious diarrheas, irritable bowel syndrome, antibiotic-associated diarrhea and bloating.
What evidence of benefit is there?
The American Gastroenterological Association recently published a technical review of studies with probiotics and clinical guidelines derived from them. Although over 2400 scientific articles were reviewed, evidence of benefits was judged to be low, and the guidelines were conditional. For adults and children taking antibiotic therapy, there was evidence that some specific probiotics reduced the chance of developing Clostridium difficile diarrhea. For preterm newborns, specific probiotic cocktails are recommended to reduce the chance of developing necrotizing enterocolitis, but again, the recommendation was conditional.
Specific probiotics were recommended conditionally for treatment of “pouchitis,” inflammation of the surgically-constructed neorectum after colectomy. The AGA recommended against probiotics for acute infectious gastroenteritis, and recommended treatment only in clinical trials for inflammatory bowel disease and irritable bowel syndrome.
The bottom line on probiotics
Nevertheless, some people see great benefit from specific probiotics. Since there is little harm and rare serious complications from using probiotics in generally healthy people, it makes some sense to try one if you have a digestive problem that might benefit from treatment.
Be cautious though: probiotics are not interchangeable, so don’t assume that all have identical effects. The truth is that some of the products on the market may not even have living bacteria in them. Keep in mind, they are not regulated as drugs by the Food and Drug Administration and do not have to be of proven value to be sold. It is wise to talk to your doctor about which probiotic might give you the digestive health that you’re seeking.
Su GL, Ko CW, Bercik P, Falck-Ytter Y, Sultan S, Weizman AV, Morgan RL. AGA Clinical Practice Guidelines on the Role of Probiotics in the Management of Gastrointestinal Disorders. Gastroenterology. 2020 Aug;159(2):697-705. doi: 10.1053/j.gastro.2020.05.059. Epub 2020 Jun 9. PMID: 32531291.
Preidis GA, Weizman AV, Kashyap PC, Morgan RL. AGA Technical Review on the Role of Probiotics in the Management of Gastrointestinal Disorders. Gastroenterology. 2020 Aug;159(2):708-738.e4. doi: 10.1053/j.gastro.2020.05.060. Epub 2020 Jun 9. PMID: 32531292; PMCID: PMC8018518.