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

Founded by Marco Kleijn, Netherlands

Chavanco

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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.

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.
 
FMT Clinics
  1. I included all required info
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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).
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.
 
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
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.
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.
 
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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
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
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
That is not what I claimed.

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

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.
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.
 
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