Presumed Safety of Probiotics Questioned

In certain medical conditions, probiotic supplements may actually make things worse.

If you’ve ever made sauerkraut at home, you know you don’t have to add any kind of starter bacteria to get it to ferment, because the lactic acid-producing bacteria are already present on the cabbage leaves themselves out in the field. This suggests that raw fruits and vegetables may not only be a source of prebiotics—that is, fiber—but also a source of “novel” probiotics. 

As I discuss in my video Culture Shock: Questioning the Efficacy and Safety of Probiotics, researchers have since worked on characterizing these bacterial communities and found two interesting results. First, “the communities on each produce type were significantly distinct from one another.” Indeed, the tree fruits harbor different bacteria than veggies on the ground, and grapes and mushrooms seem to be off in their own little world. So, if these bugs do indeed turn out to be good for us, this would underscore the importance of eating not just a greater quantity but also a greater variety of fruits and veggies every day. And, second, the researchers found that there were “significant differences in [microbial] community composition between conventional and organic” produce. “This highlights the potential for differences in the microbiota [or bacteria] between conventionally and organically farmed produce items to impact human health”—but we don’t know in what direction. They certainly found different bacteria on organic versus conventional produce, but we don’t know enough about fruit and veggie bugs to make a determination as to which bacterial communities are healthier.

What about probiotic supplements? I’ve talked before about their potential benefits in my videos Preventing and Treating Diarrhea with Probiotics and Gut Feelings: Probiotics and Mental Health, but there appears to be publication bias in the scientific literature about probiotics. This is something we see a lot with drug companies, where the sponsor, such as the supplement company paying for its own probiotic research, may not report negative results. It won’t publish it, as if the study never happened. In that case then, doctors just see the positive studies.  

As you can see at 2:00 in my Culture Shock: Questioning the Efficacy and Safety of Probiotics video, using fancy statistical techniques, researchers estimated that as many as 20 unflattering studies “with smaller or deleterious results” were simply MIA. They just weren’t published. What’s more, even in the studies that were published, even when the authors were directly sponsored by a yogurt company, for example, “very commonly conflicts of interest are not reported…”

There’s also been concerns about safety. A review for the government’s Agency for Healthcare Research and Quality concluded that there’s “a lack of assessment and systematic reporting of adverse events in probiotic intervention studies,” so while “the available evidence in RCTs [randomized controlled trials] does not indicate an increased risk [for the general public]…the current literature is not well equipped to answer questions on the safety of probiotic interventions with confidence.”

Let’s talk about the study that freaked people out a bit. Acute pancreatitis, sudden inflammation of the pancreas, is on the rise and can become life-threatening in some cases, as bacteria break through our gut barrier and infect our internal organs. Antibiotics don’t seem to work, so how about probiotics? They seemed to work on rats. If you cause inflammation by cutting the rats open and “mechanically damaging” their pancreas, not only do probiotics show “strong evidence for efficacy,” but there were “no indications for harmful effects…” So, half the people with pancreatitis got probiotics, and the other half got sugar pills. As you can see at 3:37 in my video, the mortality rates shot up in the probiotics group compared to placebo within ten days. More than twice as many people died on the probiotics. Thus, probiotics for acute pancreatitis probably aren’t a good idea, and, even further, probiotics “can no longer be considered to be harmless”…

The researchers were criticized for not cautioning patients about the risk before they signed up for the study. (The study subjects were told probiotics had a long history of safe use with no known side effects.) In response to the criticism, the researchers replied that there were no known side effects—until their study.

At the start of this blog, I alluded to my Preventing the Common Cold with Probiotics? video.


Perhaps it would be safer and more effective to focus on fostering the growth of good bacteria by feeding them prebiotics (fiber and resistant starch). Learn more:

In health, 

Michael Greger, M.D.

PS: If you haven’t yet, you can subscribe to my free videos here and watch my live presentations:

Should You Get an Annual Physical Exam?

What are the risks and benefits of getting a comprehensive annual physical exam and routine blood testing?

The model of getting an annual physical exam dates back nearly a century in American medicine, but recently, many health authorities “have all agreed that routine annual checkups for healthy adults should be abandoned”—yet, the majority of the public still expects not only a comprehensive annual physical exam, but also extensive routine blood testing. “Given the gap between patients’ enthusiasm for and [the new] guidelines’ skepticism about annual head-to-toe examinations, what are physicians to do?” As I discuss in my video Is It Worth Getting an Annual Physical Exam?, “first, we must educate patients about preventive practices of proven and unproven benefit.” For example, the only routine blood test currently recommended by the USPSTF, the official preventive medicine guidelines setting body, is cholesterol.

The reason “why many physicians continue to perform annual examinations of patients’ hearts, lungs, abdomens and even reflexes and continue to order some of the tests that have been proven ineffectual or even harmful” is because, otherwise, the patient might leave unsatisfied with the visit. “Evidence suggests that the more thorough physicians are (that is, the more physical and laboratory examinations they perform), the better patients feel about their health and their physicians.” So, they are like “placebo clinical manoeuvers…But rather than performing unnecessary (and sometimes contraindicated) physical exams and laboratory tests during an annual visit, perhaps physicians should spend some of the time saved by telling their patients why they are not examining their abdomens, hearts and lungs”—that is, why are aren’t just going to go through the motions like some witch doctor. 

“Most important, we need to educate ourselves about the dangers of overdiagnosis….There will always remain a small possibility that our examination might detect some silent, potentially deadly cancer or aneurysm. Unfortunately for our patients, these serendipitous, life-saving events are much less common than the false-positive findings that lead to invasive and potentially life-threatening tests,” wrote a doctor from the Cleveland Clinic. He went on to share a story about his own father who went in for a checkup. Can’t hurt, right? His dad’s physician thought he felt what might have been an aortic aneurism, so he ordered an abdominal ultrasound. Can’t hurt, right? His aorta was fine, but something looked suspicious on his pancreas, so a CT scan was ordered. Well, that can hurt—it’s a lot of radiation—but thankfully, his pancreas looked fine. But…what’s that on his liver? It looked like cancer, which made a certain amount of sense since his dad had worked in the chemical industry. Realizing how ineffective the treatments were for liver cancer, he realized he was going to die.

His daughter was not ready to give up on him, though, and convinced him to see a specialist. Maybe if they cut it out, he could live a few more years. But first, they had to do a biopsy. The good news was he didn’t have cancer. The bad news, though, was that it was a benign mass of blood vessels, so when they stuck a needle in it to biopsy, he almost bled to death. He required ten units of blood—and ten units is about all you have! This resulted in pain, thus morphine, thus urinary retention, and thus a catheter, yet, thankfully, no infection. Just a bill for $50,000. 

The frustrating thing is that there wasn’t any malpractice or anything in the whole horrible sequence. Every step logically led to the next. “The only way to have prevented this [life-threatening] outcome would have been to dispense with the initial physical examination”—the “checkup” that couldn’t hurt, right?

“Why, then, do we continue to examine healthy patients? First of all, we get paid to do it.” His dad’s initial doctor only received a hundred bucks or so, but just think about all that “downstream revenue” for the hospital and all the specialists. Overdiagnosis is big business.

“Too many patients bear the costs and harms of unneeded tests and procedures,” but without annual check-ups, we doctors would miss out on all those opportunities for “open communication and interpersonal continuity…” Is that so? In that case, replied one physician, if you want communication, why not just take your patients out to lunch? 

“Of course, such lunches should fairly and ethically be preceded by an informed consent discussion that allows prospective diners to understand the risk that they will be infantilized, made dependent, and may well receive unnecessary and injurious diagnostic and therapeutic interventions as a consequence of that grilled cheese and soup”—particularly, I would add, if you’re feeding your patients grilled cheese, having already chalked up your first such “unnecessary and injurious” act!

So, if you don’t have any symptoms or issues, should you even have an annual check-up? That was the subject of my last video, Is It Worth Getting Annual Health Check-Ups?.

Should All Children Have Their Cholesterol Checked, too? Watch the video to find out!

Check out this video to Find Out If Your Doctor Takes Drug Company Money.

I sometimes stumble across these peripheral issues and fall down various rabbit holes. For example, I’ve got a whole series of videos on various diagnostic tests such as mammograms. I don’t want to get too far away from nutrition, but whenever I learn something new and interesting—particularly if there are conflicts of interest trying to muddy the waters—I feel compelled to try to share to help set the record straight.

In health,

Michael Greger, M.D.

PS: If you haven’t yet, you can subscribe to my free videos here and watch my live presentations:

Should You Get an Annual Health Check-Up?

What are the risks and benefits of getting an annual check-up from your doctor?

Physicians and patients have come to expect the annual check-up as a routine part of care. “However, considerable research has not demonstrated a substantial benefit,” so a “revolt is brewing against the tradition of periodic” check-ups. “Even the Society for General Internal Medicine advised primary care physicians to avoid ‘routine general health checks for asymptomatic adults.’”

As I discuss in my video Is It Worth Getting Annual Health Check-Ups?, routine check-ups do seem to make sense. But, historically, medical practice has included all sorts of interventions that seemed to make sense, such as hormone replacement therapy for menopause—that is, until it was put to the test and found to increase risks of breast cancer, blood clots, heart disease, and stroke. “History repeatedly shows that good intentions and ‘common sense’ kill in the name of prevention (for example, prone sleeping recommendation for infants).” Indeed, doctors killed babies by making the so-called common sense recommendation that infants sleep on their tummies, whereas we now know “Face Up to Wake Up.” “We should always demand evidence rather than succumb to delusion.”

“We check our cars regularly, so why shouldn’t we also check our bodies…?” Well, unlike cars, our bodies have self-healing properties. To see if the benefits outweigh the harms, researchers decided to put it to the test.

“What are the benefits and harms of general health checks for adult populations?” The bottom line is that check-ups were “not associated with lower rates of all-cause mortality, mortality from cardiovascular disease, or mortality from cancer,” meaning they weren’t associated with living longer or a lower risk of dying from heart disease, stroke, or cancer. So, general check-ups may not reduce disease rates or death rates, but they do increase the number of new diagnoses. And, the “[h]armful effects of some tests and subsequent treatment could have balanced out possible beneficial effects of others.”

Possible harms from check-ups include “overdiagnosis, overtreatment, distress or injury from invasive follow-up tests, distress due to false positive test results, false reassurance due to false negative test results, possible continuation of adverse health behaviours due to negative test results, adverse psychosocial effects due to labelling, and difficulties with getting insurance” (now that you have a pre-existing condition), not to mention all of the associated costs. 

Take diabetes, for example. Wouldn’t it be great if we detected cases of diabetes earlier? Perhaps not, if you were one of the people given Avandia, the number one diabetes drug that was then pulled off the market because instead of helping people, it appeared to be killing them. Adverse drug events are now one of our leading causes of death. When it comes to lifestyle diseases like type 2 diabetes, maybe we should focus instead on creating healthier food environments. This is what one of my favorite organizations, Balanced, does to help prevent the diabetes epidemic in the first place.

How many times have you tried to inform someone about healthy eating and evidence-based nutrition, only to have them say, “No, I don’t have to worry. My doctor reassured me I’m fine. I just had a check-up, and everything’s normal.” As if having a normal cholesterol is okay in a society where it’s normal to drop dead of a heart attack, the number one killer of men and women. It would be one thing if you went to see a lifestyle medicine doctor who spent the check-up giving you the tools to prevent 80 percent of chronic disease, but given the way medicine is currently practiced, it’s no wonder why the history of routine check-ups “has been one of glorious failure, but generations of well meaning clinicians and public health physicians struggle to allow themselves to believe it.” But, “policy should be based on evidence…” 

Poor diet may be “on par with tobacco smoking as the most common actual causes of death,” yet the medical profession is inadequately trained in nutrition. Worse, nutrition education in medical school appears to be declining. If you can believe it, there is actually a “shrinking of formalized nutrition education” among health professionals, so the advice you get during your annual check-up may just be from the last tabloid your doctor skimmed while in the supermarket check-out line.

“And screening appointments should not be regarded as a form of ‘health education,’” read one medical journal editorial. “People who are obese know very well that they are, and if we have no means of helping them…then we should shut up.” Well, if you really have nothing to say that will help them, maybe you should shut up, especially those doctors who say they “have no idea what constitutes a ‘healthy’ diet”—although we do know that veggies and nuts are a good start.

Won’t a check-up allow your physician to do a comprehensive physical exam and routine blood testing? I discuss that, as well as the pros and cons, in my vide Is it Worth Getting an Annual Physical Exam?.

Did I say lifestyle medicine? Yes! Learn more about this exciting growing field in Lifestyle Medicine: Treating the Causes of Disease and Convincing Doctors to Embrace Lifestyle Medicine. Make sure your doctor is a member of the American College of Lifestyle Medicine (and even better certified by the American Board of Lifestyle Medicine).

Still don’t understand how there can be risks? See Why Prevention Is Worth a Ton of Cure. Unfortunately, physicians and patients alike wildly overestimate the benefits of pills and procedures. See, for example, The Actual Benefit of Diet vs. Drugs.

The fact is Physicians May Be Missing Their Most Important Tool.


And what about mammograms? See my video series:

In health,

Michael Greger, M.D.

PS: If you haven’t yet, you can subscribe to my free videos here and watch my live presentations: