One of the fallacies that some of us who work in health care can fall into is the "If it works for one thing, it must work for everything." One of the things I hear thrown around as a cure-all for everything is yogurt. Constipated? Eat yogurt. Diarrhea? Eat yogurt. Taking antibiotics? Eat yogurt. Need to "build up" your immune system? Eat yogurt. Poor appetite? Eat yogurt. Appetite needs suppressing? Guess what, eat yogurt! And why are we supposed to eat yogurt? Because the "good bacteria" or the "active cultures" in it "helps restore the natural balance of the colon." This "good bacteria" is so important that even the yogurt haters or dairy intolerant can get probiotics in pill form, juice form, fermented tea form, etc. Let me first remind you that the scientific name for what you are referring to is "probiotics" which are defined as live microorganisms that are thought to be beneficial to the host organism. And not only are they supposed to "restore balance" to colon (whatever that means) but they have a host of other health related claims associated with them. What does the evidence say?
First of all, let's talk about the main home of the bacterial strains, your colon. According to Mark Crislip, MD, the colon contains a "metaphorical rainforest," meaning that it is a complicated, interactive system of hundreds of species of bacteria. This environment has now been termed a micro biome and is estimated to contain 100 trillion microbes. These lovely little microorganisms have a big job—that of filling up spaces in the lining of the bowel (mucosa) so that other pathogenic bacteria (aka "bad guys) can get a toe-hold there. Other jobs include helping us digest and absorb certain foods and even helping us make essential vitamins that we are normally unable to manufacture as humans. If you are a 12 year old boy or anyone else who finds jokes about flatulence amusing, you will be happy to know that our gut flora helps provide the source of your amusement. The mix of species that resides in our guts is constantly being replenished as there is always some fecal flora in or covering everything including the food and drink you consume, and the loved ones you hug (even the germ phobic ones). Some scientists have now estimated that there are at least three main enterotypes now, meaning that the mix of gut flora you have might eventually be categorized just like your blood type is. (1, 2)
Now let's take a look at the strains of probiotics found in yogurt and other related products. There is a fairly impressive amount of types of bacteria out there, and some of them even have names that sound similar to the type of flora found in humans. But here's the kicker; none of the strains found in the probiotic supplements are the same type as what's found in the human GI tract. They might do an excellent job of making cheese, or giving yogurt or buttermilk their distinct taste and texture, or giving Kombucha tea a fizzy finish, but they are still not the same as what's found in humans. And even though there are several types of bacteria in the probiotic products, they come no-where near the complexity of what we already have.
So if you are an average person that is not being treated for an infection or receiving chemotherapy for cancer, your digestive tract already has the proper amount of gut flora in it to crowd out any pathogens and it is being replenished by what you eat. It is unlikely you would need to eat yogurt or take any of the other probiotic options. Typically these products are going to be marketed as helping you "maintain gut health" or once again, "keep the natural balance of the colon" which means…..absolutely nothing. Your gut already has what it needs, and your daily food intake will keep replenishing it. For some people, they might even have increased bloating and flatulence because of the increase in foreign bodies (which if you are a 12 year old boy, might be a good way to win a contest). To focus on a daily probiotic intake would be like (once again quoting Dr. Crislip) "putting a putting green in the middle of a rainforest." In other words, it looks strange, it's probably expensive, and there really isn't any purpose to it.
I can think of at least one patient, and unfortunately some health care providers, that would immediately start crowing about how eating yogurt, etc once or twice a day made them have regular bowel movements. Unfortunately, many people are unaware that constipation is defined as less than three bowel movements per week, so if they fall into the "every other day" category they get panicky. Also, many of the people I work with take medications that do cause constipation, whether it be pain medication, psychiatric medication, etc. So, people will get told either by celebrity endorsers or even by their health care providers that they should eat yogurt (often a specific brand) in order to "speed up their intestinal transit time." Their consumption of yogurt most likely will speed up their intestinal transit time, but the reason it does so it that the body recognizes a foreign substance and does what the body normally does when it senses an invader—tries to get it out as quickly as possible. You didn't make any changes to your gut flora—you just got rid of an invader. Once you stop eating the yogurt you will likely have decreased transit time, but not because you "took aware what was restoring gut health," you just took away the invader. SkepticRD's evil sarcastic twin wants you to know that if you ate Salmonella, that would also "naturally" speed up your digestive tract as well. Now, if you do have painful constipation from your pain medicine that you have to take and you start eating a yogurt like Activia 1-3 times per day you will be spending $20-60 per month on average, get 70-210 calories per day that you likely don't need, and 11-33 net carbs per day that take away from your daily allowance (and that's for the lite version!). In contrast, you could go to your local drugstore and buy their brand of the commonly used Senna and pay about $10 for 100 tablets. So yes, the probiotics do help with constipation—but at a high cost in money and calories depending on your source. (To be fair, someone might also buy probiotic capsules and pay $6-12 dollars for 100 capsules. But, you often have to take more than one per day, and there is no regulation to guarantee the product has what it say it has in it).Now what if you catch some kind of infection and need to take antibiotics to clear it up? Won't the antibiotics wipe out your normal gut flora? Should you take probiotics when you start the treatment? Here there does actually seem to be some evidence to support that taking probiotics does help prevent antibiotic induced diarrhea. Now keep in mind that the probiotics that you are taking are not the same as what's found in your body normally, but you will at least be populating your colon with something that's not pathogenic. To go back to the rain forest analogy; if the land is cleared by fire you might as well plant something, hopefully something that doesn't make the soil quality worse. It will never be quite the same as what was there before. Keep in mind too, that if you already have diarrhea, there is little evidence that taking probiotics will help.
Speaking of diarrhea (told you this blog was full of bugs!), do probiotics help? If you have diarrhea from a "virus," a bacterial infection, a parasitic infection, or an inflammatory bowel disease like Crohn's disease, this is usually referred to as "inflammatory diarrhea" and you could actually make the problem worse. In this case, you can think of the lining of bowel as looking like your knee might look if you fell off your bike (also called "road rash"). If you already have the road rash, you want to make sure the cuts don't get any deeper right? And you are probably going to clean it up and bandage it to keep anything else from inflaming it more right? If you have inflammatory diarrhea then taking probiotics is akin to having someone sneeze all over your open wound and rubbing it in—you'll probably get a worse infection and further skin breakdown. You want to keep your bowel lining intact to keep the bugs from spreading to other parts of your body and to do that you keep the inflammation under control. There might also be a similar process that happens if you are an immunocompromised person like someone who has AIDS or has undergone treatment for cancer. If those foreign bacteria get out of your colon and into the rest of you blood stream your body now has to try to battle an infection it wasn't prepared for.
If you have survived the conversation about diarrhea, let's talk about one of the other reasons that people take probiotics; to "build their immunity." At least one yogurt company has used the tag line "70% of you immunity is in your digestive system." There is truth to this; people existed without refrigeration for thousands of years so chances are our bodies evolved to help us get rid of anything nasty we might have ingested. But I think many people hear "building your immunity" as "I'm not going to catch that cold that my kid brought home." Remember, ingesting foreign strains of bacteria does solicit an immune response in the colon to get rid of the things that shouldn't be there, but all that immune response is in an inflammation in the colon wall. Therefore, in this situation, boosting your immunity = more diarrhea, not that you won't get colds, etc. (Link)
Now some of you yogurt lovers are going to keep eating it because, well, you like it. To make sure you are actually getting some sort of health benefit from your hard earned money, however, try to find brands that have the least amount of sugar and the most protein and fat to help you get something that your body could actually use. Your average fruit flavored yogurt gives you about 30 gms of carb and 200+ calories from that added sugar. In contrast, a plain Greek yogurt might give you 6 grams of carb and 80-90 calories. Check your label, always!
Take home message—Your average person will not get any benefit from taking probiotics . In some cases, they might even do harm to your wallet or your health.