Some people claim that we're better off getting our probiotic bacteria from dirt than from foods like yogurt. But are these products safe?
What Are the Advantages of Soil-Based Organisms?
Proponents of soil based organisms argue that they are sturdier than the usual food-based bacteria. They don't require refrigeration or special handling. They are more resistant to acid, so more of them survive the trip through the stomach to the intestines. All that may be true. The question is whether the supplements are beneficial--or safe.
Some of these strains may be beneficial, others are probably pathogenic.
In order to answer either question, you'd have to know exactly which organisms you're talking about. Most commercially available products include lots of different strains, the vast majority of which have not been studied in humans, alone or in combination.
Some soil-based organisms may be beneficial to humans, others are probably pathogenic. But how they behave will depend very much on how much you take, which bugs you already have on board, and the health of your gut when you take them. Not surprisingly, people with health problems are more likely to have adverse reactions.
What Is the Research on Soil Based Probiotics?
I found only one product with published clinical research. A very small but placebo-controlled trial found a soil-based probiotic called Prescript-Assist offered modest relief from IBS symptoms. It's not much--but it's a whole lot more than most of the other products out there. A competitor's website, for example, lists a number of placebo-controlled trials which found that their product lowered cholesterol, improved the white blood cell count of leukemia patients, and improved memory and concentration in healthy subjects. Despite these amazing results, none of these studies were published in peer-reviewed scientific journals.
In my experience, anyone who goes to the trouble of conducting a controlled trial and gets amazing results is going to try to publish them. And it's a little hard to imagine that a journal would reject such novel findings--unless the methodology, reporting, or sources of the study were seriously questionable.
Should You Take Soil-Based Organisms?
Because they are classified as dietary supplements and not drugs, manufacturers and distributors of probiotics have a pretty long leash. The FDA and FTC occasionally go after companies for making false or misleading claims--but the internet is rife with incredible testimonials, unsubstantiated statements, and highly questionable "research." Meanwhile, spot-checks by government agencies, researchers, and consumer watchdog groups regularly find that products contain far fewer (or completely different) bacteria than the label indicates.
If you're simply interested the potential for soil-based organisms to promote overall health, I think I would stick to food sources such as natto and raw vegetables. Go play in your garden and you'll likely pick up a few more. If you're interested in SBOs as a therapy for IBS, Crohn's Disease, or other conditions affecting the health of your digestive system, I would definitely enlist the help of a medical professional who can evaluate the evidence for a particular product in view of your circumstances.
I'm indebted to Dr. Michael Schmidt of the Medical University of South Carolina and the American Society of Microbiology for helping me make sense of this vast and complex topic. If you find this subject as fascinating as I do, be sure to check out their surprisingly entertaining podcast "This Week in Microbiology" and the other resources on their website at MicrobeWorld.org.
Safety of Probiotics to Reduce Risk and Prevent or Treat Disease, prepared for the US Department of Health and Human Service by the US Agency for Healthcare Research and Quality