Prescript Assist is a Risky Supplement

What is Prescript Assist?

Prescript Assist is a popular probiotic supplement in the paleo community because it’s marketed as following ancestral principles. The claim is that this product contains microorganisms found in soil, which are “natural” and what our ancestors consumed with their unwashed produce. Some of the claims of this product are the following:

  • It can survive the harsh conditions of the gastrointestinal tract
  • It can colonize the gut
  • It has beneficial organisms in it
  • It has clinical evidence behind it
  • The product has prebiotics that will feed the bacteria in the product

Wow! The product seems like a miracle that addresses so many difficulties encountered by lactic-acid bacteria probiotics. The old Prescript Assist formula had 29 species of “soil-based organisms," the new formula has 28, with several new species replacing old ones. Here are some of the microbes that are included in it:


  • Red text = Not known to be found in humans
  • Gray text = mixed evidence (some opportunistic pathogens)
Old FormulaNew Formula
Arthrobacter agilisArthobacter globiformis
Arthrobacter citreusAzospirillum brasilense
Arthrobacter globiformisAzosprillum lipoferum
Arthrobacter luteusAzotobacter chroococcum
Arthrobacter simplexAzotobacter paspali
Acinetobacter calcoaceticusAzotobacter vinelandii
Azotobacter chroococcumBacillus amyloliquefaciens
Azotobacter paspaliBacillus atrophaeus
Azospirillum brasilienseBacillus licheniformis
Azospirillum lipoferumBacillus megaterium
Bacillus brevisBacillus pumilus
Bacillus maceransBacillus subtilis
Bacillus pumilusBacillus thuringiensis
Bacillus polymyxaBacillus firmus
Bacillus subtilisBrevibacillus brevis
Bacteroides lipolyticumCellulomonas fimi
Bacteriodes succinogeneKurthia zopfii
Brevibacterium lipolyticumMicrococcus luteus
Brevibacterium stationisNocardioides simplex
Kurthia zopfiiPseudomonas fluorescens
Myrothecium verrucariaPseudomonas putida
Pseudomonas calcisRhodobacter sphaeroides
Pseudomonas dentrificansRhodococcus rhodochrous
Pseudomonas fluorescensRhodopseudomonas palustris
Pseudomonas glatheiRhodospirillum rubrum
Phanerochaete chrysosporiumStreptomyces griseus
Streptomyces fradiaeStreptomyces griseoflavus
Streptomyces cellulosaeStreptomyces venezuelae
Streptomyces griseoflavus

Let’s first explore whether it makes any sense to include these strains in a probiotic supplement. Some questions to consider:

  • Are these microorganisms found in the human GI tract?
  • Are these microbes found in foods that humans regularly eat?
  • How do these microbes interact with each other?
  • How do these microbes interact with human microbes? Will they produce antibiotics that could kill human bacteria?
  • What effects will they have on the immune system? Are they safe?
  • Have been they tested in large human studies, what about animal models?
  • Have they been tested over long periods of time?

Let’s do some investigative research. Searches of MEDLINE, the database of studies that are searchable using the search engine PubMed yield almost no human or animal results for several of these microorganisms. Species colored red lack evidence in humans as being probiotics while those shaded gray are mixed (some of them have been found to be opportunistic pathogens in different areas of the body, and there’s *rare* evidence that some of them may be beneficial*).

In fact, a lot of these organisms are used for agricultural and industrial purposes, and several of the listed species above are known to produce antibiotics. One thing to consider is that if these organisms are spore-forming, antibiotic-producing bacteria, then it’s very possible that several of them (the clear majority in this product, which has not been studied) are competing with microorganisms in the gut for resources.

The Clinical Evidence

However, the old formulation claims to be tested in a clinical trial and claims to be beneficial for symptoms of IBS. In fact, most of the paleo community and several folks such as Chris Kresser and Sarah Ballantyne have promoted the product because of this clinical evidence. Let’s look at this study.

Here are the positives of this study

  • A randomized trial with a placebo as a control
  • Double-blinded
  • Used a repeated-measures ANCOVA for data analysis (this increases the precision of the data)

Real limitations

  • Only two weeks long
  • Had 26 participants
  • Used an IBS questionnaire that is not validated
  • Atrocious reporting of the study (then again, it's an old study, so it's somewhat understandable)

A randomized trial with 26 participants, that’s only two weeks long should not be used to market a product. There is a reason drugs and interventions must go through *extensive* testing before they’re allowed to be marketed as being effective for a condition/disease. Small sample sizes have lots of variability in the data and give imprecise results. If you want to understand why sample sizes are so important, see my article here. And with something like the microbiome, a two-week study does not justify the safety of this product.

Yet, several leaders in the paleo sphere have been affiliates for this product and were hesitant to recommend the new formulation because it didn’t have the clinical evidence to back it, however, the clinical evidence to back the product in the first place was never strong!

Are Probiotics a Waste of Money?

Probiotic supplementation does have research behind it as an intervention for several outcomes. If you want to see this research, look at my comprehensive table here, where I gather some research surrounding probiotic supplementation.

If you’re going to ingest microorganisms to improve your health, you want to make *sure* that they’re safe and that they’ve been tested rigorously in human trials. If you're going to be a bit more cutting edge because you’re desperate, you may at least want to be sure that the theory behind what you’re ingesting is sound.

For example, probiotics with lactic acid bacteria are found in fermented foods, like yogurt, which seems to be linked with improved health outcomes. They’ve been tested in in-vitro studies (Petri dishes), in animal models, and in humans. Fecal transplants make sense hypothetically, take bacteria from someone healthy and insert it into someone who’s not so healthy. It’s been tested in animal models, and it’s been successful in human trials for Clostridium difficile infections and is being investigated for several other outcomes.

Putting random organisms from the soil (a vast ecosystem, with who knows how many bacteria, doesn’t seem like a good idea). Especially when there’s no evidence to suggest these will have any help.

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2 thoughts on “Prescript Assist is a Risky Supplement

  1. Great article, Zad. However, in regards to “Are these microorganisms found in the human GI tract?”, Saccharomyces cerevisiae var. boulardii Biocodex strain is also not found in the GIT but there are extensive studies showing its benefits. It is found in the skin of lychees. My question to Prescript-Assist is, soil based organisms based on WHAT soil sample? SBOs from Kentucky, Mumbai, Hawaii? From where? It’s flawed thinking.

    • Analia, my problem isn’t just that it’s not found in humans, but also that there is practically no evidence behind it. Most probiotic supplements are often not found in human GI tracts, but they have extensive evidence behind them, which I’ve written about.

      What’s also interesting about Prescript Assist is that it’s a fertilizer product that seems to have been repacked as a probiotic. The fertilizer product has the exact same species found in Prescript Assist. The name of the soil fertilizer is Biogenesis I Non-Polymer Soil I Biological Soil Inoculant. Sold by Tainio Biologicals Inc

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