WARNING: Gezonde Darmflora / Marco Kleijn – Comprehensive Review & Scam Alert Gezonde Darmflora

[Chavanco]

I am writing this to warn others about Gezonde Darmflora and its owner, Marco Kleijn. After extensive research and correspondence, I have concluded that his products are ineffective, scientifically flawed, and potentially a scam. The focus here is clearly profit over patient safety. Here is a breakdown of why you should stay away.

1. The "Reviews" are suspicious and likely fake​

The first red flag is the website's review section. I have read all of them carefully, and they follow an identical structure and wording. About 95% of them end with variations of "Thank you Marco for all your help, you're a savior!!" which feels incredibly fake and staged.

• No negative feedback: The only mixed reviews are several years old, and there's only a couple of them from many years back. It's statistically impossible to have a 4.7/5 rating without recent negative reports, especially in the FMT field where success rates vary naturally. We also already know that many people are dissatisfied with his products.
• Manipulation: It is blatant that he curates and fabricates reviews to maintain a high score.

2. Critical Flaws in Manufacturing (Why the capsules are likely dead/not working)​

This is the most concerning part. Marco admits to practices that kill the beneficial bacteria before they ever reach you.

• A) The Blender Issue (Oxidation & Bacterial Death): The most critical bacterias for gut repair (like for instance Faecalibacterium prausnitzii) are strictly anaerobic, meaning they die instantly upon contact with oxygen.
  • Marco's Admission: When I asked via email if he avoids mechanical mixing to protect these bacteria, he replied: "No, we use a blender."
  • The Science: Using a blender in a normal room creates a vortex that whips oxygen into the stool. Established research dictates that processing must happen in a controlled environment to preserve viability.
  • The Problem: Marco does not use a nitrogen-filled anaerobic chamber. By blending stool in open air—even "shortly"—he is subjecting the microbiome to massive oxidative stress. The specific "super-bacteria" you are paying over €525 for are destroyed before the freezing even begins.
• B) The "2-Hour" Rule is Dangerous: The website states donors have 2 hours to process the stool into capsules. This contradicts professional medical standards.
  • Viability Decay: Studies on fecal preservation show that leaving stool at room temperature causes a rapid bloom of aerobic bacteria (like E. coli) and the death of beneficial anaerobes.
  • Kitchen vs. Lab: In clinical studies, time from defecation to freezing is minimized to minutes. Allowing a 2-hour window in a donor's home allows for fermentation and degradation that renders the "Super-Donor" status irrelevant.
• C) "Remote Donors" & The Fake Lab: He claims stool goes "direct in a laboratory freezer (-80°C)". However, he also lists "Remote Donors" (e.g., Donor DF6 is listed as living in Germany, while Marco is in the Netherlands).
  • The Reality: These donors are making capsules in their home kitchens. There is no way a donor in Germany is freezing capsules to -80°C instantly and shipping them without damage. The "lab" environment he claims is just a residential kitchen.

3. Unverified Donors & Lack of Screening​

I sent Marco a list of standard strict donor criteria (vaginal birth, breastfed, never smoked, no alcohol, etc.).

• Evasive Answers: His response was just a dismissive "Of course." He refused to provide proof or specifics.
• Contradictions: He claims "no medication use," yet documents show donor DF4 is vaccinated against Covid (which strict FMT protocols often flag).
• No Monitoring: He admits they do not use diet logs. You have no idea if your donor ate junk food, smoked a cigarette or drank alcohol the day before your batch was produced. You are simply told to "trust" that they are disciplined.

4. Dangerous & Profit-Driven Medical Advice​

Marco is not a doctor; he is a self-proclaimed "hobby expert." His advice contradicts clinical science and seems designed to sell more pills.

• The "Few Days" Myth: His website claims that if you don't feel effects in the first few days, the donor is a "wrong match." This is false. Clinical studies often require 6+ weeks to assess FMT colonization.
• The Upsell: He suggests that if symptoms return, you should buy a second or a third dose immediately. A true "super-donor" transplant usually requires one course, or maximum 2 (after several weeks has passed). This is a tactic to extract more money from desperate patients.
• Low Dosage: His standard course (24 capsules) equals approx. 17g of stool, if even that. Clinical standards are often 30-50g, or even higher. He under-doses you, then tells you to buy more because of your "antibiotic history" is making the cure less effective. It is not. He just wants you to buy more.

5. Who is Marco Kleijn? (Identity & Credibility)​

• The "We" Facade: The website uses words such as "we" and "us" to sound like a professional clinic. In reality, it is a one-man operation running a "drop-shipping style business".
• The "Football Pro/News Papers" Lie: He claims to be a former professional football (soccer) player. I spent hours searching archives, news outlets, and sports databases. There is zero record of him proving that.
• No Media Presence: Despite claims of being in several news outlets talking about his FMT success stories, there are no articles about him. The only thing I found was a LinkedIn account, which is also very generic and empty, without any profile picture.

Conclusion:​

Gezonde Darmflora charges premium prices (€525) for a product that is:

1. Oxidized (dead bacteria due to low effort blenders).
2. Processed at home by unsupervised donors with little to no experience.
3. Under-dosed.
4. Pretty much worthless.

The seemingly high success rate is mathematically impossible given his flawed methods. Do not waste your money on what is essentially a €650 placebo. This is a seller focused on profit, not a medical professional focused on cure.

Stay away, and feel free to inform others about this bad FMT provider too.

 

[Michael Harrop]

Some of this I agree with, and is already listed in the wiki: https://humanmicrobiome.info/where-to-get-fmt/#gezonde-darmflora

1. The reviews - Yes, they don't seem real.

2. Manufacturing flaws - I disagree that this is the most concerning.

I agree that blending is not ideal, but it is widely done by doctors and laypeople who still get decent results.

Time to process - you can see in the wiki that room temperature for up to 3 hours, and refrigeration for up to 72 hours seems ok: https://humanmicrobiome.info/fmt/#methodologyprocedure

3. Lack of info on donors - yes.

4.

A true "super-donor" transplant usually requires one course, or maximum 2 (after several weeks has passed).

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That is for C. diff only. Other conditions require much longer treatment. https://humanmicrobiome.info/fmt/#frequency

"A true super-donor" is extremely rare, and I don't see him making claims that his donors are super-donors.

 

[Chavanco]

2. Manufacturing flaws - I disagree that this is the most concerning.

I agree that blending is not ideal, but it is widely done by doctors and laypeople who still get decent results.

Time to process - you can see in the wiki that room temperature for up to 3 hours, and refrigeration for up to 72 hours seems ok: https://humanmicrobiome.info/fmt/#methodologyprocedure

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Manufacturing flaws are the most concerning part, precisely because this is where the damage happens before the patient even receives the product. "Decent results" from laypeople does not mean the treatment is optimal - it just means the patients don't die or becomes severely ill.

You say it's "widely done by doctors and laypeople who still get decent results". The problem is that the wiki reference measures DNA composition, not bacterial viability. (Papanicolas et al., 2019 - https://doi.org/10.1038/s41598-019-48131-1) showed that samples processed in air vs. anaerobically had identical DNA profiles, but 19% vs. 50% viable bacteria.

They also found a 12-fold reduction in Faecalibacterium prausnitzii - one of the most important anti-inflammatory bacteria. (Bénard et al., 2023 - https://doi.org/10.3390/microorganisms11081973) confirms that obligate anaerobic bacteria die during aerobic processing.

That "room temperature for up to 3 hours seems ok" is misleading when measuring DNA rather than viability. (Gratton et al., 2016 - https://doi.org/10.1016/j.metabol.2016.09.007) found that metabolite changes (fermentation) occur after just 1-5 hours at room temperature. (Ott et al., 2004 - https://pubmed.ncbi.nlm.nih.gov/15016799/) showed significant reduction in bacterial diversity after 8 hours at 4°C - well below the 72 hours.

Claiming that manufacturing flaws are not the most concerning, assumes that DNA profile = therapeutic effect. It does not. It is viability (live bacteria) that determines whether FMT actually works. The difference between 19% and 50% viability could be decisive for chronic conditions.

4.
That is for C. diff only. Other conditions require much longer treatment. https://humanmicrobiome.info/fmt/#frequency

"A true super-donor" is extremely rare, and I don't see him making claims that his donors are super-donors.

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The claim that super-donor is only for C. diff, and that other conditions require much longer treatment is not supported by research as far as I'm concerned.

El-Salhy et al. (2020) used one super-donor for IBS patients and achieved 89.1% response after a single 60g FMT (https://doi.org/10.1016/j.cgh.2019.04.034). Symptom remission in 47% vs 5.5% placebo. No need for repeated courses.

Moayyedi et al. (2015) identified super-donor effects for Ulcerative Colitis (not C. diff), where 7 of 9 remission patients received FMT from the same donor (https://pmc.ncbi.nlm.nih.gov/articles/PMC6624363/).

That super-donors are extremely rare is also misleading, as El-Salhy found his donor through systematic screening of several candidates and not by luck. The criteria are known: high microbial diversity, rich in Bifidobacterium and butyrate producers.

Regarding Marco: He does not explicitly market "super-donor", but his pricing (€525) and claimed 70-75% success rate implies he is selling donor stool as a premium product. Whether his donors are actually super-donors is impossible to verify.

 

[Michael Harrop]

Manufacturing flaws are the most concerning part, precisely because this is where the damage happens before the patient even receives the product

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Manufacturing details are trivial compared to donor quality. Being able to trust that the donor is safe and will not make you worse is the most important factor. So the details that show Gezonde Darmflora is an untrustworthy source are the most concerning.

You say it's "widely done by doctors and laypeople who still get decent results". The problem is that the wiki reference measures DNA composition, not bacterial viability

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Irrelevant. They achieve decent success for the conditions (usually C. diff) they're treating. That's all I meant. I already agreed that it's not optimal.

The claim that super-donor is only for C. diff

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That is not what I claimed.

El-Salhy et al. (2020) used one super-donor

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• https://forum.humanmicrobiome.info/threads/fecal-microbiota-transplantation-influences-microbiota-without-connect.561/post-1863
• https://forum.humanmicrobiome.info/threads/continued-letters-and-complaints-to-the-fda-nih-and-hhs-jan-2025-fmt.842/

That super-donors are extremely rare is also misleading, as El-Salhy found his donor through systematic screening of several candidates and not by luck. The criteria are known: high microbial diversity, rich in Bifidobacterium and butyrate producers.

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This is nonsense. It's partly addressed right above, and partly addressed by the fact that I've screened 1.4 million stool donor applicants and still haven't found a "super-donor".

Your claim about super-donor criteria needs a citation.

 

[SFBayFMT5]

1. The "Reviews" are suspicious and likely fake​

The first red flag is the website's review section. I have read all of them carefully, and they follow an identical structure and wording. About 95% of them end with variations of "Thank you Marco for all your help, you're a savior!!" which feels incredibly fake and staged.

Click to shrink...

I got my opinion of the effectiveness from real-time messaging back and forth with previous recipients of GD's product, who I did NOT find through Marco himself. I would encourage everyone to do this, with any provider, i.e. find the most authentic-seeming customers you can find who are independent of the company.

2. Critical Flaws in Manufacturing (Why the capsules are likely dead/not working)​

This is the most concerning part. Marco admits to practices that kill the beneficial bacteria before they ever reach you.

• A) The Blender Issue (Oxidation & Bacterial Death): The most critical bacterias for gut repair (like for instance Faecalibacterium prausnitzii) are strictly anaerobic, meaning they die instantly upon contact with oxygen.

Click to shrink...

Marco actually is the most adamant about lack of oxygen exposure of anyone I've seen who runs a FMT business. Even major hospitals and stool banks didn't use anaerobic chambers for much of the time they were doing FMTs--maybe that's changed, but Michael is right that there have been successes without.

• B) The "2-Hour" Rule is Dangerous: The website states donors have 2 hours to process the stool into capsules. This contradicts professional medical standards.

Click to shrink...

Back when I used OpenBiome, they processed stool within 6 hours of donation, and it still worked (for me). Others weren't as successful with them as I was, but still, much less stringent time frames have been used in successful studies in the past.

• C) "Remote Donors" & The Fake Lab: He claims stool goes "direct in a laboratory freezer (-80°C)". However, he also lists "Remote Donors" (e.g., Donor DF6 is listed as living in Germany, while Marco is in the Netherlands).

Click to shrink...

He actually buys these remote donors their own -80C freezers for their own homes! He told me this in an email exchange with him. Local Dutch donors donate their stool directly at their facility in Hillegom.

3. Unverified Donors & Lack of Screening​

I sent Marco a list of standard strict donor criteria (vaginal birth, breastfed, never smoked, no alcohol, etc.).

• Evasive Answers: His response was just a dismissive "Of course." He refused to provide proof or specifics.

Click to shrink...

What do you expect, him giving private medical information to strangers over the internet?

• Contradictions: He claims "no medication use," yet documents show donor DF4 is vaccinated against Covid (which strict FMT protocols often flag).

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It is very true that a sizeable number of recipients don't want vaccinated donors (I personally don't care). He is sensitive to this and provides this information clearly on the website. Most people would define "medication use" as current, regular taking of medication, not a one-time dose of something possibly three or more years ago. This is not "lying".

• No Monitoring: He admits they do not use diet logs. You have no idea if your donor ate junk food, smoked a cigarette or drank alcohol the day before your batch was produced. You are simply told to "trust" that they are disciplined.

Click to shrink...

Which FMT suppliers DO use diet logs?? Not even HM does, to my knowledge. You have to consider that many potential donors would find this requirement too burdensome, hence you'd lose some otherwise potentially very effective donors.

4. Dangerous & Profit-Driven Medical Advice​

Marco is not a doctor; he is a self-proclaimed "hobby expert." His advice contradicts clinical science and seems designed to sell more pills.

• The "Few Days" Myth: His website claims that if you don't feel effects in the first few days, the donor is a "wrong match." This is false. Clinical studies often require 6+ weeks to assess FMT colonization.
• The Upsell: He suggests that if symptoms return, you should buy a second or a third dose immediately. A true "super-donor" transplant usually requires one course, or maximum 2 (after several weeks has passed). This is a tactic to extract more money from desperate patients.

Click to shrink...

There's a difference between enough of a benefit to tell that a transplant is having an effect, vs. the full benefit. I've always noticed significant changes within the first few days--improvements for helpful transplants and worsening for bad transplants. However, the full benefit requires 1-2 months.

I agree that re-trying with the same donor again is unlikely to be helpful or necessary if the first try failed, especially if the method is the same. I've not had a mediocre donor make me dramatically better upon trying him or her a second time. With DF7, for instance, I tried once with capsules, then later with enema--the effect of the enema was marginal even though I got several times the amount of stool in the same amount of time that way.

• Low Dosage: His standard course (24 capsules) equals approx. 17g of stool, if even that. Clinical standards are often 30-50g, or even higher. He under-doses you, then tells you to buy more because of your "antibiotic history" is making the cure less effective. It is not. He just wants you to buy more.

5. Who is Marco Kleijn? (Identity & Credibility)​

• The "We" Facade: The website uses words such as "we" and "us" to sound like a professional clinic. In reality, it is a one-man operation running a "drop-shipping style business".

Click to shrink...

HM is just as much of this--in fact HM has donors ship directly to customers, whereas GD never does that.

The claim that super-donor is only for C. diff, and that other conditions require much longer treatment is not supported by research as far as I'm concerned.

Click to shrink...

I agree.

That super-donors are extremely rare is also misleading, as El-Salhy found his donor through systematic screening of several candidates and not by luck. The criteria are known: high microbial diversity, rich in Bifidobacterium and butyrate producers.

Click to shrink...

These criteria are just an educated guess, based on what I suspect is actually a misunderstanding of what many of us with gut issues actually need. And tellingly, nobody has actually tested donors like that head-to-head with donors with a different profile and showed that it was more successful. It's possible, if not probable, that SOME recipients benefit from high butyrate producers, particularly those with ulcerative colitis seem the most likely, but I suspect that need is a lot less common than most in the field suspect it is.

(As a side note, if you want someone who definitely shares that viewpoint, check out Mark Davis and Probiotic Infusions).

Regarding Marco: He does not explicitly market "super-donor", but his pricing (€525) and claimed 70-75% success rate implies he is selling donor stool as a premium product. Whether his donors are actually super-donors is impossible to verify.

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That price isn't outrageously high for FMT.

 

[Michael Harrop]

I got my opinion of the effectiveness from real-time messaging back and forth with previous recipients of GD's product, who I did NOT find through Marco himself. I would encourage everyone to do this, with any provider, i.e. find the most authentic-seeming customers you can find who are independent of the company.

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This is not a remotely valid approach. Most of the people recommending specific providers and claiming good results from them are very obviously paid or incentivized to do so.

What do you expect, him giving private medical information to strangers over the internet?

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That's pretty dishonest. Those are not private medical information, especially when the donor is anonymous. Human Microbes provides that information.

Regarding the vaccination thing, I don't think most people consider vaccinations to be "medication use". But "no medication use" is pretty vague, and may not refer to lifetime usage.

Not even HM does, to my knowledge.

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It's appropriate that you're recognizing HM as the eminent comparison.

I agree.

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You agree with one of their most nonsensical statements? What a surprise.

That price isn't outrageously high for FMT.

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Only because others are also charging outrageously high prices.