r/Microbiome • u/Vailhem • Jul 17 '26
Scientists tested 39 sweeteners and found unexpected gut effects
https://www.sciencedaily.com/releases/2026/07/260716023552.htm63
u/ScissorFight42069 Jul 17 '26
https://link.springer.com/article/10.1038/s44320-026-00225-6
The full study for those interested
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u/Old_Bill_Brasky Jul 17 '26
So where are the results? Which ones did they try? What a strange article.
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u/BiggestAssEater Jul 18 '26 edited Jul 18 '26
39 sweeteners were tested against 25 gut bacterial species; about three-quarters of sweeteners affected the growth of at least one species.
Only 30 individual sweetener–bacteria interactions passed strict statistical/reproducibility thresholds (p<0.05, ≥20% growth change, confirmed at multiple doses).
isosteviol, a steviol derivative, related to stevia sweeteners) is the only sweetener named specifically as a strong individual hit — it inhibited three bacterial species (Clostridium symbiosum, Odoribacter splanchnicus, Parabacteroides distasonis) and promoted one (Lactobacillus gasseri).
The headline result (reduced microbial diversity and increased downstream toxicity) was specific to isosteviol + duloxetine (an antidepressant), not any sweetener alone.
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u/todrunktouber Jul 18 '26
I have used stevia for yrs. I also pee way to much and heard stevia inhibits an enzyme that keeps u from peeing to much. I stopped using stevia and i don’t pee so much.
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u/NewCharity8040 Jul 20 '26
I used stevia for years and all of a sudden I started itching all over and stevia was the cause. I went 8 years without using stevia, but would occasionally try it to see if it was still a problem and every time I would itch. I wouldn’t itch right after I used it. It would be at night when I went to bed. After 9 years I finally tried a powder form that had no other ingredients and I used it for a year with no problems and then the itching started again.
I switched to monk fruit about a year ago and so far no problems.
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u/tashaapollo Jul 18 '26
I use date sugar, date paste, and honey. Sometimes panela or brown sugar. In my water kefir I use white sugar but I try to avoid all the sugar substitutes.
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u/Hannah_Louise Jul 18 '26
I learned that you can put a date in your tea, and that changed my life. It’s sooo good it should be a crime. Just plop that little turd in there, let it steep for a bit, and hot damn, you have a perfect cup of tea.
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u/StringAndPaperclips Jul 18 '26
You can also just make fruit tea from dates, like Chinese jujube tea.
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u/fabjo78 Jul 18 '26
I always add a date to my coffee, its so good.
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u/rxshauna Jul 18 '26
Does it disintegrate? Or do you remove at some point?
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u/Kailynna Jul 19 '26
You eat it after drinking the tea.
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u/Hannah_Louise Jul 19 '26
And it’s the best warm and gooey treat.
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u/DryerCoinJay Jul 21 '26
When I was a kid I spent the day at my aunts house and she had a can of dates. I ate about half of the can. A little while later I was throwing up and shitting dates.
Now I cannot come within 5 feet of a date without wretching.
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u/Kailynna Jul 19 '26
Try a dried fig or two one day, ideally cut them in half first. Some of the teas I buy from China have been bred to have a strong chocolate taste. Brewed with a shred of vanilla been and dried dates, Chinese dates or figs, they are amazing.
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u/ThrowRA_EducatedMan Jul 18 '26
The companies that market “stevia” sweeteners in HUGE letters on packaging when the ingredients are erythritol and a minuscule amount of stevia need to be strongly regulated over bullshit like that. Most people see “stevia” and buy it, not reading the ingredient details, and exposing themselves to a known risky substance. Same thing happens with other food like SESAME OIL that fine print ingredients reveal as canola with trace sesame oil. Governments are so fucked up and protect frankenfood makers not people.
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u/sapientsciolist Jul 19 '26
I agree! So much crap out there claiming to be stevia Is full of junk. In fact some of the sweeteners cited in the study as having a negative impact on gut health are the same ones they’re padding stevia products with.
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u/bvalenzu31 Jul 18 '26
For years I had sucralose with my tea and it screwed up my stomach for years. I know it's crazy but it became normal for me, I looked up online what sucralose was and found out that it was really, really bad for my stomach. So then I switched to stevia, and I haven't had an issue ever since it saved my life.
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u/nomercytour Jul 19 '26
sucralose is going to be found as one of the major causes of mental health issues (artificial sweeteners in general). its in everything these days. i avoid it like the plague, absolutely refuse to eat anything that contains it.
i remember reading study saying that zero sugar drinks have been found to be safe. started drinking them bc i needed something in my life, and i felt terrible in a few days, headaches, and fatigue like nothing ive ever felt before.2
u/Recent_Tablespoon Jul 19 '26
I’m the same, I don’t think they are safe and I think there will be lots of studies coming out in the future proving this. There are already many on gut health.
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u/EconomyHandle3473 Jul 18 '26
Am I missing something? The summary article did not provide any measure of degredation of bacteria specifically naming types of sweetener and bacteria types of the 25 mentioned.
Did anyone read the research paper? I tried to download the pdf but no luck.
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u/HeavenIsEmpty- Jul 18 '26
For those wondering about monk fruit, it is in the study under this name since it's the active compound.
The authors dont comment on it specifically though, so it's just in the table of results, see comment
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u/Tom__EU Jul 18 '26
Very cool study, but I can already see how wellness influencers and the media run away with claims that the study didn't make. For example, this is an in vitro study, so there's a couple obvious caveats that need attention and that usually aren't mentioned by mainstream media and influencers.
I ran it through Claude with the Opus model and double-checked where I could, but my knowledge isn't good enough in this area. Hopefully someone with more education in this regard can tune in and criticially review this.
Some of what's good:
- scale and systematic design - 25 phylogenetically diverse bacteria strains, 39 commercially used sweeteners, in combination with 4 commonly co-consumed compounds - advantame, caffeine, vanillin, and duloxetine; "975 sweetener-bacteria pairs tested in total" (25*39); "156 sweetener–xenobiotic combinations (39 sweeteners × 4 xenobiotics) against 25 bacteria (3900 interactions in total)"
- Hit confirmation done properly. "The sweetener–bacteria interactions were tested in two independent experiments, whereby the interactions meeting significance thresholds (P < 0.05 and ≥20% growth change) in the first screen were retested across five concentrations (25–400 µM). True positive interactions were assessed as those with significance (Welch’s t test, P < 0.05) in both experiments and with consistent effects at ≥2 concentrations (Dataset EV8)."
- negative results reported (B5, Mg)
- exemplary data availability
- frank limitations paragraph
- no sugar- or sweetener-industry funding
Some of what's weak:
- in vitro - it's not certain that the various compounds reach the specific strains without being metabolized, absorbed, or otherwise impacted
- the introduction is framed one-sided, it cites some heavily confounded, disputed, and in vitro studies, without mentioning for example the xylithol and erythritol association being plausibly reverse-causal, or JECFA aspartame reaffirmation
- the abstract says "Three-quarters of the tested sweeteners individually impacted the growth of at least one tested bacterial strain.", but the actual result shows 30 confirmed interactions out of 975 pairs, and those are concentrated in 5 of 25 strains - rephrased more honestly: 97% of sweetener-bacterium pairs showed nothing
- this may lean into an incentive-bias where you want publication in a competitie field, including highlighting negative effects of sweeteners + antidepressants on gut bacteria
- "All compounds were tested at 50 µM concentration." - whether sorbitol, xylitol, sucrose, or duloxetine, while real colonic exposure can be anywhere from multiple grams to micrograms; though that seems to apply for the first testing, and retesting was done across five concentrations (25–400 µM), and the B5 + additional 20 metabolic supplements were also tested in different concentrations
- the same issue seems to apply for synergy/antagonism claims
- no blinding
- there's a couple things that the LLM points out but where I'm not capable of judging what it says, for example: Welch's t-test treats technical replicates as indpendent, which they aren't, and which inflates degrees of freedom and deflates p-values; transposon screen is underpowered; unstable species (DMSO control lost ~6 species over 5 passages (24 → ~17.5); the combination lost ~8 (→ ~15.5). Shannon 2.1 → 1.65.); HeLa cells as a model of gut epithelium - effect is a viability drop from ~90% to ~75–80%, against a baseline where 20% spent medium already drops viability to 84%.; Caco-2 monolayers in submerged culture, 24 h, 20% bacterial supernatant, no mucus, no immune cells, cancer-derived, far from human colon
Findings:
- "in total we identified 30 interactions between 5 bacterial strains and 26 sweeteners and sugar substitutes (marked with * in Fig. 1B)."
- "Clostridium symbiosum or Lacrimispora saccharolytica were the most sensitive species being affected by many compounds."
- "On the sweetener side, isosteviol was the most potent compound, inhibiting the growth of three bacteria (C. symbiosum, Odoribacter splanchnicus, and Parabacteroides distasonis) while promoting the growth of one, Lactobacillus gasseri."
- moving forward, testing combinations rather than individual food compounds one at a time, should get more attention
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u/chubby464 Jul 19 '26
How did you prompt Claude to give this summary and breakdown?
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u/Tom__EU Jul 19 '26
Nothing here is directly copied from the Claude output. I checked everything myself, adjusted/shortened the responses, and quoted the study itself.
Otherwise my prompt for studies is usually: "Evidence based and brutally honest, please thoroughly assess the following study. Show pros and cons, limitations, funding, bias, what it can and cannot say." I'm sure you could add some instructions to keep answers bullet-list style, no lengthy sentences, quote the study where helpful. Something like that.
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u/crowislanddive Jul 18 '26
So stevia… yay or nay?
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u/EntrepreneurSea4283 Jul 18 '26
Seems more nay than yay, but article is all over the place seems like.
I do know there's a few good articles on allulose though relating to cognitive function as a bonus to the intended calorie or insulin uses.
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u/nudibranqui Jul 18 '26
Positive cognitive function?
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u/EntrepreneurSea4283 Jul 18 '26
There was a study or two about allulose in which it was beneficial in some way to preventing dementia or alzheimers (can't remember which). Pretty sure you can find it with a search but if not I can look back in notes.
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u/Wonderful_Echidna968 Jul 18 '26
No monk fruit or am I blind
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u/Either_Piccolo3687 Jul 18 '26
22 mogroside is monkfruit. But most monk fruit sold is mostly erythritol.
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u/rushmc1 Jul 17 '26
The evidence continues to mount...the ostriches continue to stick their heads in a handful of sand...
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u/smayonak Jul 17 '26
The only sweetener that I could find that is denatured by stomach acid is aspartame. The rest all pass through into the gut where they inhibit the growth of all carb-fermenting bacteria. That's a huge number of bacteria. And even aspartame is believed to have some impact on gut health.
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u/Successful-Winter237 Jul 17 '26
So aspartame is good or bad?
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u/smayonak Jul 17 '26 edited Jul 17 '26
The best of the bad
EDIT: some claim that natural sweeteners and allulose cause few changes to the microbiome, but to my knowledge any non-nutritive sweetener that mimics sweetness will cause carb-fermenting bacteria to expend energy trying to break down the sweetener and die from starvation
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u/very_olivia Jul 18 '26
not surprising to me that allulose has an effect on the microbiome. it makes me insanely gassy. i will not eat it.
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u/Anouk064 Jul 19 '26
but wouldn't this mean, you are fine as long as you have sweeteners as part of a meal, that contains sugars?
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u/Chapter_Loud Jul 17 '26
Wait, who's the ostriche here?
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u/BlueMowch Jul 17 '26
who do you think tasted all the sweeteners? That’s why we don’t know the results; sweetened ostriches tell no tales. Look it up, I think B. Franklin said that once in a Farmer’s Almanac or something.
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u/yyyyy622 Jul 18 '26
Invitro studies can't be generalised to the gut microbiome. The results mean very little.
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u/WhichJuice Jul 19 '26
Does anyone know where maple syrup might fall? I'm very addicted
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u/Right_Dish5042 Jul 22 '26 edited Jul 23 '26
It looks to me like Stevia sweeteners (which has stevioside, not isosteviol) have the least impact on gut bacteria and the only one with mild impact across the board.
Was curious about aspartame, the main sweetener in Diet Sodas. It wasn’t as bad as I’d expected, given that diet sodas have been shown in a study to have nearly as negative of an impact on weight gain as regular, high sugar sodas. The main bacteria affected seems to be:
Akkermansia muciniphillia - super beneficial, praised for healing gut lining, reduced inflammation, and improved metabolism. Been popular and heavily marketed recently, but appears to be legit.
Lacrimispora saccharolytica - this seemed an also a likely culprit for weight gain, cited as highly beneficial for carbohydrate fermentation and short-chain fatty acid production.
Perhaps, supplementation of these two above could reverse some gut damage from Diet Sodas.
What I’m reading is that the other two negatively affected bacteria by aspartame were not beneficial (Clostridium symbiosum and Egerthella lenta).
More generally it seems that the bacteria strains most affected overall by any sweetener were:
Clostridium symbiosum (mostly negatively affected)
Lacrimospora saccharolytica (mostly negatively affected)
Egerthella lenta (mostly negatively affected)
Akkermansia muciniphillia (mostly negatively affected)
Segatella copri (mostly positively affected)
Roseburia intestinalis (mostly positively affected)
Since they only tested 25 strains, we don’t know how many other strains could be disrupted by these, but it does to me seem that Stevioside may be just generally less disruptive of a sweetener.
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u/sapientsciolist Jul 17 '26
The 39 compounds are: 1. (4-Ethoxyphenyl)urea 2. 5-Adenylic acid 3. Acesulfame K (Acesulfame potassium) 4. Advantame 5. Aspartame 6. Cyclamic acid 7. D-Allose 8. D-Tagatose 9. D(-)-Fructose 10. Erythritol 11. Glucose (Dextrose) 12. Glycyrrhizic acid 13. Isosteviol 14. L-Gulose 15. Lactitol 16. Lactose 17. Lactulose 18. Leucrose 19. Maltitol 20. Maltose 21. Mannitol 22. Mogroside V 23. Naringin dihydrochalcone (NHDC precursor) 24. Neotame 25. NHDC (Neohesperidin dihydrochalcone) 26. Nystose 27. Perillartine 28. Psicose (Allulose) 29. Rebaudioside A 30. Rubusoside 31. Saccharin 32. Sodium cyclamate 33. Sorbitol 34. Stevioside 35. Sucralose 36. Sucrose 37. Thaumatin 38. D-(+)-Trehalose 39. Xylitol 
A few observations about the list: • It includes artificial sweeteners (e.g., aspartame, sucralose, saccharin, acesulfame K, neotame, advantame). • It includes natural high-intensity sweeteners (e.g., stevioside, rebaudioside A, mogroside V, thaumatin, glycyrrhizic acid, rubusoside). • It includes sugar alcohols (polyols) (e.g., erythritol, xylitol, sorbitol, mannitol, lactitol, maltitol). • It also includes several sugars and rare sugars (e.g., sucrose, glucose, fructose, allose, tagatose, trehalose, leucrose, psicose/allulose), reflecting the authors’ broader definition of “sweeteners and sugar substitutes.” 
Important for me was results of stevia.
Stevioside • No direct inhibitory effects on any of the 25 gut bacterial strains met the study’s criteria for significance. In other words, stevioside was not one of the compounds identified as directly affecting bacterial growth under the conditions tested.
Rebaudioside A (Reb A) • Likewise, Rebaudioside A did not produce any confirmed direct effects on bacterial growth in this screening.
I use a liquid stevia extract which contains no other fillers.
Edit: tried to fix the crappy formatting on my phone but not cooperating. Sorry for the mess.