Probiotics are a big and rapidly growing business, with annual global sales of products expected to rise to $42 billion by 2016. The term probiotic refers to dietary supplements (tablets, capsules, powders, lozenges and gums) and foods (such as yogurt and other fermented products) that contain “beneficial” or “friendly” bacteria. The organisms themselves are also called probiotics.
They are promoted to improve digestion, strengthen immunity, help in weight loss and even protect against periodontal disease, among other proposed benefits, as well as for general health. Will the friendly bacteria in these supplements and foods keep you healthy?
Proponents claim that probiotics (meaning “for life,” as opposed to antibiotics) confer health benefits primarily by rebalancing the normal microflora in the large intestine (colon). There are many general types of bacteria used as probiotics (two common ones are Lactobacillus and Bifidobacterium), and many different species as well as strains within species. They have different physiological effects—and thus possibly different health benefits (as well as possible risks). Some yeasts, such as Saccharmyces, can also act as probiotics.
Probiotic products may contain a single strain or many strains, and the number of organisms in a daily dose can range from 1 billion to more than 250 billion. Many manufacturers boast that their products contain unique probiotics and/or combinations of strains that make them even better for you—and often charge a premium price.
Probiotics: what the studies show
The large intestine is home to hundreds of trillions of bacteria. Fortunately, most are neutral or even beneficial, performing many vital body functions. For example, they help keep “bad” bacteria at bay, play a role in immunity, help us digest food and absorb nutrients and may even have anticancer effects. But will consuming them as probiotics in foods or capsules make a notable difference to your health—especially if you are already healthy? Here’s a look at the evidence.
Digestive problems. The best support for probiotics is for reducing diarrhea, especially some kinds of infectious diarrhea and diarrhea associated with antibiotic use. A 2010 review from the Cochrane Collaboration concluded that probiotics shorten episodes of acute infectious diarrhea. And in 2011, a Health Canada monograph stated that products containing certain probiotics (such as Lactobacillus rhamnosus GG) help manage acute infectious diarrhea and antibiotic-associated diarrhea.
A 2012 research review published in the Journal of the American Medical Association (JAMA) found that probiotics reduced the risk of antibiotic-associated diarrhea by 42 percent—but many of the studies had flaws, so these findings should be interpreted with caution. A 2013 Cochrane review of 23 trials also concluded that probiotics may be effective for preventing antibiotic-related diarrhea. However, the largest and best-designed study to date, published in the Lancet in 2013, found that probiotics were no better than a placebo in preventing diarrhea in older people taking antibiotics.
Some studies suggest that certain probiotic strains also help in mild to moderate ulcerative colitis (a type of inflammatory bowel disease) and possibly for bloating and gas in irritable bowel syndrome (IBS). If you have mild to moderate ulcerative colotis or IBS, probiotics may be a helpful adjunct treatment. One product that has some research behind it for irritable bowel conditions is VSL#3, a combination of eight different probiotic strains, to be used under a doctor's supervision.
A 2010 review of five controlled studies, published in the World Journal of Gastroenterology, found that certain strains of B. lactis and L. casei improved stool consistency and frequency of bowel movements in people with constipation.
Immunity and colds/flu. There’s a close connection between the bacteria in your colon and the immune system—and probiotics have been linked to enhanced immune responses (such as to flu vaccines). Several studies, including one published in 2012 in the British Journal of Nutrition, have found that certain probiotic strains boost measures of immune response—but whether this translates into any clinical benefits is uncertain. Studies have been inconsistent, for example, as to whether taking probiotics will actually curb colds and other upper respiratory infections. A 2011 Cochrane review concluded that probiotics may help prevent such infections, though there were limitations in the studies and no data for older people.
Weight loss. There’s little published clinical work showing that probiotics will help promote weight loss, as some manufacturers claim or imply. A study in the European Journal of Clinical Nutrition in 2011 found that people who drank fermented milk with a particular strain of Lactobacillus gasseri for 12 weeks had a reduction in abdominal fat and body weight, compared to those consuming a control drink. Another study, published in the Journal of Functional Foods in November 2012, found that people who consumed yogurt containing two “novel” strains of probiotics experienced small losses in body fat, but no changes in body weight.
Oral health. In addition to the microflora that reside in the large intestine, bacteria populate the mouth as well. An increasing number of probiotic lozenges and gums are thus being promoted for oral health—for example, to reduce periodontal disease, throat infections and bad breath. There’s preliminary evidence that certain strains may have some benefits, but commercial products may not have the same strains and formulations as those tested in published studies. Don’t expect these products to replace brushing and flossing.
Other uses. Many other claims are made for probiotics—that they lower blood pressure and cholesterol, alleviate skin conditions like eczema, treat ulcers and urinary tract infections, improve vaginal health, prevent colon cancer, ease anxiety and depression and ward off traveler’s diarrhea. Good evidence to support these claims is lacking.
Testing by ConsumerLab.com of 29 probiotic products in 2012 found that while all contained at least one billion organisms per daily dose ("an amount that may provide some benefit"), some had far lower amounts than claimed on the label.
Side effects: Probiotics are considered safe overall for healthy people; short-term side effects may include mild gas and bloating. But keep in mind that if they do have physiological effects, these may not always be good effects. Some may, at least in theory, overstimulate the immune system or adversely affect metabolic pathways such as carbohydrate metabolism. If you are immune-compromised, have certain bowel problems or are seriously ill in other ways, avoid probiotics unless your doctor has okayed their use. Probiotics should be used cautiously by pregnant women, infants and young children and never given to premature infants.
Bottom line: Probiotics are a promising field of research and may one day be used to treat or help prevent many disorders. But there’s not enough solid evidence to recommend their widespread use. Vague claims that probiotics "support good digestive health" are meaningless. Larger, longer and better studies are needed to test specific strains for specific conditions and to determine the proper doses and regimens.
Originally published March 2013. Updated March 2014.