Benefits of Probiotics Remain Unproven
Health Letter, July 2017
By Sarah Sorscher, J.D., M.P.H.
In recent years, interest in the human microbiome has exploded, opening up future possibilities for medical treatment. The trillions of tiny microbes — referred to as the microbiome —living within our gut, on our skin, in our mouth and nose, and on other parts of our bodies weigh more than one pound in adults. These microbes offer profound health benefits, helping us process nutrients, driving out harmful organisms, and even modifying the body’s immune response to disease.[1],[2]
The food and dietary supplement industries have been swift to capitalize on the excitement around microbes by selling products that contain probiotics, or live microorganisms purported to improve health by altering the microbiome. Industry currently pulls in an estimated $35 billion per year worldwide from these products, a number that is projected to balloon to over $50 billion by the end of the decade.[3]
Although naturally occurring microbes undoubtedly play an important role in human health, no probiotic has been approved by the Food and Drug Administration for medical treatment, and there is very little high-quality scientific evidence that backs up claims that probiotics can be used successfully to treat or prevent disease.[4] Learn which claims have been tested in clinical trials — and why many probiotic supplements are very likely a waste of money.
Cultivating the microbiome
A typical human body contains trillions of single-celled organisms, most of which are bacteria found in the gut,[5],[6] which outnumber human cells by 10 to 1. This collection of microbes begins colonizing the body at birth and evolves over time, varying between individuals.[7]
The makeup of the microbiome can be affected by an individual’s behavior, with poor eating habits possibly associated with negative changes and the growth of harmful bacteria.[8] By contrast, eating a diet rich in fruits and vegetables may contribute to a healthy, diverse microbiome by offering beneficial bacteria the food they need to thrive.
Evidence for benefits of probiotics
One source of evidence of benefits from probiotics comes from studies involving gastrointestinal conditions, including diarrhea.[9] A number of randomized controlled clinical trials have tested probiotics for treating the kind of diarrhea that can occur when the normal microbial balance of the gut is disrupted. This can occur when a person takes antibiotics, is exposed to new harmful microbes while traveling, or undergoes radiation therapy to the pelvis or abdomen for cancer. These trials have provided limited evidence that probiotics can shorten the duration of infectious diarrhea,[10] reduce the chances of having diarrhea while travelling,[11] and help prevent diarrhea that often occurs during pelvic radiation treatment for cancer.[12]
However, these studies have varied greatly in terms of the dosages and species of bacteria used.[13],[14] Also, not all studies have identified a benefit. In 2013, the distinguished medical journal The Lancet published results from a high-quality randomized controlled trial involving nearly 3,000 elderly subjects who were being treated with antibiotics. That study found that treatment with probiotics did not decrease overall diarrhea rates, nor did it help prevent diarrhea caused by the harmful bacterium Clostridium difficile.[15]
Probiotics also have been studied for other gastrointestinal conditions. The bacterium Helicobacter pylori is a common cause of stomach ulcers, which often are treated with antibiotics accompanied by a drug used to suppress stomach acid, like esomeprazole (NEXIUM). Several randomized controlled trials, again involving multiple dosages and strains of probiotics, have suggested that adding these supplements to the typical antibiotic and stomach acid treatment may increase the chances of successfully eliminating H. pylori and avoiding the side effects of diarrhea and nausea that are common with standard H. pylori treatment. However, these data were also not conclusive.[16],[17],[18] ,
Researchers also have explored whether probiotics are effective in treating the symptoms of irritable bowel syndrome (IBS). Several studies, one of which was funded by the probiotics industry,[19] have appeared to show that probiotic supplementation may improve the symptoms of IBS, including pain, bloating and flatulence.[20],[21],[22] Yet this research is limited because many of the studies have suffered from possible bias, some have failed to show benefits and no specific probiotic strain and dosage has consistently proven effective for this condition across multiple trials.[23]
Probiotics also have come up short for other gastrointestinal conditions. Although patients with Crohn’s disease and ulcerative colitis have been shown to have less microbial diversity in the gut,[24] reviews of probiotic treatment for such patients generally have found insufficient evidence that probiotics have a significant benefit.[25],[26]
There is even less evidence of benefit for conditions in other areas of the body. The microbiome may play a role in diabetes[27] and obesity,[28] allergies,[29] and respiratory infections.[30] Yet, so far, research in these areas is too preliminary to recommend taking probiotics for these conditions.
| Don’t Believe the Label’s Description of the Contents
Some manufacturers of probiotics may attempt to distinguish their products by including specific strains (such as Lactobacillus or Bifidobacterium) or dosages (such as 250 milligrams or 5-10 billion “CFU”) that have been used successfully in clinical trials.[31] Yet one recent study showed that only 1 out of 16 probiotic products contained all of the specific strains advertised and that there is significant variation between lots of the same product.[32] A 1997 study by an Italian research team found similar problems.[33] |
What You Can Do
Although naturally occurring microbes undoubtedly play a substantial role in human health, there is still very little high-quality evidence that probiotic supplements are useful in preventing or treating medical conditions. In addition, many probiotics do not contain the ingredients advertised on the label (see text box).
Based on current evidence, the best way to promote a healthy microbiome is to feed your trillions of tiny biological companions well by eating well yourself. A diet rich in fiber from a variety of fruits, vegetables and whole-grain foods may help maintain microbial diversity and generally contribute to heart and digestive health.[34],[35] Avoiding unnecessary use of antibiotics will also prevent adverse changes to your microbiome.
Be sure to talk with your doctor before taking a probiotic, and never substitute one of these products for a treatment that your doctor recommends.
References
[1] National Institutes of Health. NIH Human Microbiome Project defines normal bacterial makeup of the body. June 13, 2012. https://www.nih.gov/news-events/news-releases/nih-human-microbiome-project-defines-normal-bacterial-makeup-body. Accessed April 10, 2017.
[2] Neish AS. Microbes in gastrointestinal health and disease. Gastroenterology. 2009;136(1):65-80.
[3] Scudellari M. Probiotics come with bold health claims, but the science is shaky. STAT. January 21, 2016. www.statnews.com/2016/01/21/probiotics-shaky-science/. Accessed April 10, 2017.
[5] National Institutes of Health. NIH Human Microbiome Project defines normal bacterial makeup of the body. June 12, 2012. https://www.nih.gov/news-events/news-releases/nih-human-microbiome-project-defines-normal-bacterial-makeup-body. Accessed April 10, 2017.
[6] Schneiderhan J, Master-Hunter T, Locke A. Targeting gut flora to treat and prevent disease. J Fam Pract. 2016;65(1):33-38.
[7] Clauson ER, Crawford P. What you must know before you recommend a probiotic. J Fam Pract. 2015;64(3):151-155.
[8] Simpson HL, Campbell BJ. Review article: dietary fibre-microbiota interactions. Aliment Pharmacol Ther. 2015;42(2):158-179.
[9] Schneiderhan J, Master-Hunter T, Locke A. Targeting gut flora to treat and prevent disease. J Fam Pract. 2016;65(1):33-38.
[10] Allen SJ, Martinez EG, Gregorio GV, Dans LF. Probiotics for treating acute infectious diarrhoea. Cochrane Database Syst Rev. 2010;Issue 11. Art. No.:CD003048.
[11] McFarland LV. Meta-analysis of probiotics for the prevention of traveler’s diarrhea. Travel Med Infect Dis. 2007;5:97-105.
[12] Hamad A, Fragkos KC, Forbes A. A systemic review and metaanalysis of probiotics for the management of radiation induced bowel disease. Clin Nutr. 2013;32(3):353-360.
[13] Allen SJ, Martinez EG, Gregorio GV, Dans LF. Probiotics for treating acute infectious diarrhoea. Cochrane Database Syst Rev. 2010; Issue 11. Art. No.:CD003048.
[14] McFarland LV. Meta-analysis of probiotics for the prevention of traveler’s diarrhea. Travel Med Infect Dis. 2007;5:97-105.
[15] Allen SJ, Wareham K, Wang D, et al. Lactobacilli and bifidobacteria in the prevention of antibiotic-associated diarrhoea and Clostridium difficile diarrhoea in older inpatients (PLACIDE): a randomised, double-blind, placebo-controlled, multicentre trial. Lancet. 2013;382(9900):1249-1257.
[16] Szajewska H, Horvath A, Kolodziej M. Systematic review with meta-analysis: Saccharomyces boulardii supplementation and eradication of Helicobacter pylori infection. Aliment Pharmacol Ther. 2015;41(12):1237-1245.
[17] Sachdeva A, Nagpal J. Effect of fermented milk-based probiotic preparations on Helicobacter pylori eradication: a systematic review and meta-analysis of randomized-controlled trials. Eur J
Gastroenterol Hepatol. 2009;21(1):45-53.
[18] Wang ZH, Gao QY, Fang JY. Meta-analysis of the efficacy and safety of Lactobacillus-containing and Bifidobacterium-containing probiotic compound preparation in Helicobacter pylori eradication therapy. J Clin Gastroenterol. 2013;47(1):25-32.
[19] Han K, Wang J, Seo JG, Kim H. Efficacy of double-coated probiotics for irritable bowel syndrome: a randomized double-blind controlled trial. J Gastroenterol. 2017;52(4):432-443.
[20] Moayyedi P, Ford AC, Talley NJ, et al. The efficacy of probiotics in the treatment of irritable bowel syndrome: a systematic review. Gut. 2010;59(3):325-332.
[21] Ford AC, Quigley EM, Lacy BE, et al. Efficacy of prebiotics, probiotics, and synbiotics in irritable bowel syndrome and chronic idiopathic constipation: systematic review and meta-analysis. Am J Gastroenterol. 2014;109(10):1547-1561.
[22] Didari T, Mozaffari S, Nikfar S, Abdollahi M. Effectiveness of probiotics in irritable bowel syndrome: Updated systematic review with meta-analysis. 2015;21(10):3072-3084.
[23] McKenzie YA, Thompson J, Gulia P, Lomer MC. British Dietetic Association systematic review of systematic reviews and evidence-based practice guidelines for the use of probiotics in the management of irritable bowel syndrome in adults (2016 update). J Hum Nutr Diet 2016;29(5):576-592.
[24] Kostic AD, Xavier RJ, Gevers D. The microbiome in inflammatory bowel disease: current status and the future ahead. Gastroenterology. 2014;146(6):1489-1499.
[25] Doherty GA, Bennett GC, Cheifetz AS, Moss AC. Meta-analysis: targeting the intestinal microbiota in prophylaxis for post-operative Crohn’s disease. Aliment Pharmacol Ther 2010;31(8):802-809.
[26] Naidoo K, Gordon M, Fagbemi AO, et al. Probiotics for maintenance of remission in ulcerative colitis. Cochrane Database Syst Rev 2011; Issue 12. Art. No.:CD007443.
[27] Razmpoosh E, Javadi M, Ejtahed HS, Mirmiran P. Probiotics as beneficial agents in the management of diabetes mellitus: a systematic review. Diabetes Metab Res Rev. 2016;32(2):143-168.
[28] Park S, Bae JH. Probiotics for weight loss: a systematic review and meta-analysis. Nutr Res. 2015;35(7):566-575.
[29] Osborn DA, Sinn JK. Prebiotics in infants for prevention of allergy. The Cochrane Library. 2013. Cochrane Database Syst Rev. 2013; Issue
3. Art. No.:CD006474.
[30] Cochrane commentary: probiotics for prevention of acute upper respiratory infection. Explore 2015;11(5):418-420.
[31] Schneiderhan J, Master-Hunter T, Locke A. Targeting gut flora to treat and prevent disease. J Fam Pract. 2016;65(1):33-38.
[32] Lewis ZT, Shani G, Masarweh CF, et al. Validating bifidobacterial species and subspecies identity in commercial probiotic products. Pediatr Res. 2016;79(3):445-452.
[33] Canganella F, Paganini S, Ovidi M, et al. A microbiological investigation on probiotic pharmaceutical products used for human health. Microbiol Res. 1997;152(2):171-179.
[34] Simpson HL, Campbell BJ. Review article: dietary fibre-microbiota interactions. Aliment Pharmacol Ther. 2015;42(2):158-179.
[35] Mayo Clinic. Dietary fiber: Essential for a healthy diet. September 22, 2015. www.mayoclinic.org/healthy-lifestyle/nutrition-and-healthy-eating/in-depth/fiber/art-20043983. Accessed April 4, 2017.