Have you considered adding probiotics so called “good” bacteria or yeast—to your diet to regulate your digestion, strengthen your immunity, lose weight, or improve your eczema? If so, you’re not alone. The sale of foods and supplements that contain probiotics has grown exponentially and is likely to continue to rise. This year annual sales are expected to reach about $42 billion globally. But before you add probiotic containing products to your cart, you should know what the research says they can and cannot do for you.
The gastrointestinal (GI) tract is home to trillions of beneficial bacteria and yeast that help in digesting food, clearing harmful microorganisms from the digestive system and maintaining overall gut health. These “good” microorganisms also enhance immunity to infections.
In recent times, however, improved hygiene and increased consumption of processed and sterilized foods has significantly reduced the amount of beneficial bugs that the contemporary human gut contains. Some researchers believe that the resulting change in balance between good and bad microorganisms in the gut may predispose us to more GI ailments as well as more immune and allergic conditions than our ancestors faced. Thus, the hypothesis goes, consuming probiotic products, which contain live microorganisms, will help repopulate the gut with beneficial bugs which, in turn, will help restore the balance.
Other scientists contend that this “hygiene hypothesis” is an oversimplification. They note that some probiotic products contain too few microbes to make a difference, especially considering the number that survive the trip through the GI tract and make it to the large intestine, which contains the vast majority of the microbes. (There is no consensus regarding the minimum number of microorganisms needed to ensure adequate colonization, but estimates indicate that it would take at least several billion.) Moreover, probiotics must be consumed regularly to maintain the balance.
Others propose that probiotics produce beneficial effects by stimulating the immune system or producing antibacterial compounds that keep harmful bacteria from multiplying out of control. And still others contend that probiotics work in a variety of ways and that the mechanisms of action may vary by the type of bacteria.
Clearly more investigation is needed before researchers fully understand how probiotics work. In the meantime, a growing body of scientific evidence suggests that probiotics can indeed be beneficial in certain situations. That said, there are hundreds of different genuses (such as Lactobacillus), species (such as infantis) and strains (usually a combination of letters and numbers) of probiotics, and different types and combinations have been found to be beneficial for different conditions. Not surprisingly, not every type or combination has been studied, and some types that have been studied may not be available commercially. With those caveats in mind, here’s what the latest research shows.
Which claims are credible?
There’s mounting evidence to support the value of probiotics in preventing and relieving certain GI problems and, perhaps, in boosting immunity. The research supporting other claims is weaker.
• GI upsets. Evidence supportive of probiotic use is strongest for GI problems, including diarrhea associated with the use of antibiotics, the symptoms of irritable bowel syndrome (IBS) and infection with Clostridium difficile (a bacteria that can cause recurrent diarrhea in people in hospitals and nursing homes). For example, a 2012 meta-analysis of 84 studies looking at 11 probiotic species and combinations found that they were generally beneficial for the treatment and prevention of diarrhea caused by antibiotics and C. difficile, but not for Traveler’s diarrhea. This research review, which was published in Plos ONE, also found that probiotics were useful for IBS symptoms.
Similarly, a 2013 Cochrane review of 23 studies involving more than 4,000 adults and children found that short-term use of probiotics, when taken in conjunction with a course of antibiotics, reduced the risk of developing C. difficile-associated diarrhea by 64 percent. The authors of a 2012 JAMA review of 82 studies primarily involving Lactobacillus-based products found that probiotics reduced the risk of antibiotic-associated diarrhea by 42 percent.
It’s worth noting, as the authors of these reviews did, that some of the studies included in the various analyses may be flawed; for example, they may not have described the strains used or indicated the potency of the tested product, and some may have been industry sponsored. Consequently, the findings should be considered in that context.
This is particularly true given the results from a well-designed randomized trial—the gold standard of studies—published in 2013 in The Lancet. The study, which involved nearly 3,000 hospitalized older people receiving antibiotics, found that taking a probiotic supplement containing strains of L. acidophilus, Bifidobacterium bifudum and B. lactis for 21 days was no better than a placebo in preventing antibiotic-associated diarrhea or C. difficile infection.
Of note, the PLoS ONE review discussed above also reported that L. acidipholus and B. infantis failed to show significant positive effects. But the JAMA review— which, with few exceptions, analyzed studies involving two other lactobacillus strains (L. rhamnosus or L. casei)—pointed out that results may vary by strain or species of probiotic.
• Upper respiratory infections. There is some evidence, though not terribly strong, that probiotics may reduce the chances of developing a cold or other acute upper respiratory tract infections. In a 2011 Cochrane report, researchers analyzed the results from 10 trials involving more than 3,000 children and adults in which the participants consumed yogurt or probiotic supplements for at least one week. The analysis revealed that people who consumed probiotics were less likely to develop an upper respiratory tract infection than those who didn’t. It wasn’t clear, however, whether the use of probiotics cut the duration of the infection. It’s also not known whether the findings apply to older adults, since none of the studies measured the effect of probiotics on people who were beyond middle age.
• Weight loss. Although some manufacturers say or suggest that their products promote weight loss, few published studies support that claim. One study that did show a benefit was published in 2013 in the British Journal of Nutrition. The investigators found that people who drank fermented milk with a particular strain of Lactobacillus gasseri for 12 weeks lost more abdominal fat and body weight than their counterparts who consumed a drink that did not contain the probiotic. However, they note that regular consumption might be necessary to maintain the effect.
• Other uses. Probiotics have been reported to be helpful for a variety of conditions, including high blood pressure and cholesterol, eczema, ulcers, urinary tract infections, anxiety, depression and colon cancer. For now, however, scientific substantiation of these claims is lacking.
Before you buy
In general, probiotics are safe for healthy people to consume. However, if you have a chronic or serious illness, particularly if your immune system is compromised due to a medical condition or to a medication you’re taking, talk to your doctor first.
If your goal is to fight a specific illness for which probiotics have demonstrated some efficacy, be sure that the product you choose has the particular species and strain of organism that’s been shown to be effective.
Your health care provider may be able to provide guidance regarding the best species and strains to buy for a certain condition. Also, for the greatest benefit, be sure to buy a reputable brand of product, store it appropriately to protect the live cultures and don’t use it beyond the expiration date on the package.
If you simply want to improve your digestion, some dietitians recommend that you consume traditional probiotic-containing foods on a regular basis. Fermented dairy foods like yogurt and kefir with live, or active, cultures; aged cheeses; sauerkraut or kimchi (fermented sauerkraut), miso, tempeh and soy beverages are all good choices.