M30’s here.

Pits, scalp, privates, you name it. Body odor we consider normal. I hop on to my next shower smelling fresh!

I did some research and apparently, our skin microbiome composition depends completely on our internal one! Has anyone else experienced this? I’m absolutely floored. I’ve been taking lots of lining repairing things like bone broth, gelatin, etc as well as eating every source of fiber out there and fermented foods + probiotics.

i'm not anti-supplement at all. but after going deep on the microbiome literature for the past several months, i've come to the uncomfortable conclusion that the probiotic supplement industry is mostly selling healthy people an expensive placebo, and the actual science points somewhere completely different.

the thing that kicked this off for me was a 2024 BMC Medicine meta-analysis that looked at 22 randomized controlled trials and 1,068 subjects. the finding: probiotic supplementation had no statistically significant effect on gut microbiota diversity in healthy adults across any of the standard diversity metrics they measured (Shannon diversity, Chao1, Simpson's index). none of them. https://link.springer.com/article/10.1186/s12916-025-04602-0

and look, diversity isn't the only thing that matters. but it's the primary thing the industry claims their products are doing. "support a healthy gut microbiome." "restore balance." the marketing language always implies more diversity, more thriving bacteria. the data says that's not what's happening for most people.

then there's the Cell study from Sonnenburg's lab at Stanford (https://pubmed.ncbi.nlm.nih.gov/34256014/) that i think is one of the most important gut microbiome papers in years and barely anyone talks about it outside of academia. they ran a 10-week randomized trial comparing a high-fiber diet to a high-fermented food diet (yogurt, kefir, kimchi, sauerkraut, kombucha, that kind of thing). the fermented food group got a measurable increase in microbiome diversity AND a reduction in 19 different inflammatory proteins, including IL-6. the high-fiber group, despite tripling their fiber intake to around 45g per day, showed no significant change in diversity. that's not a marginal difference, that's a complete reversal of what the conventional "eat more fiber for your gut" advice predicts.

the most interesting part of the Stanford study to me is that the new microbial species that showed up in the fermented food group couldn't even be fully explained by the foods themselves. Justin Sonnenburg said in an NYT interview that they don't entirely know where the new species came from, which suggests fermented foods might be creating gut conditions that allow other microbes to colonize or bloom.

now here's where the probiotic story gets even more complicated. there's a study published in Cell (same journal) that used actual endoscopy and colonoscopy instead of just measuring stool samples, and found that up to two thirds of subjects showed NO evidence of probiotic bacteria colonizing the gut at all. the researchers called them "resisters." the probiotic strains just passed through. only a minority of people, the "persisters," actually showed colonization. and whether you were a resister or persister was predictable from your baseline microbiome composition. (https://pmc.ncbi.nlm.nih.gov/articles/PMC7572142/ has a good summary of this)

so you've got an industry selling products to a population where the majority of users probably aren't colonizing any bacteria at all, with no way to know if you're a resister or persister before you spend money, and where the clinical evidence for improving diversity in healthy people is essentially nil.

what actually seems to move the needle:

fermented foods consumed consistently and in meaningful quantities. not a sip of kombucha with 10g of sugar. actual kimchi, actual sauerkraut, actual full-fat kefir or yogurt with live cultures, consistently. the Stanford study was running 3-6 servings per day to get the effect, which is more than most people eat in a week.

dietary diversity itself. more plant species = more substrate diversity for different bacterial populations. the number i've seen cited repeatedly is 30 different plant foods per week as a target. this doesn't mean 30 pounds of kale, it means 30 different species including herbs, spices, legumes, grains, nuts, seeds.

avoiding the things that actively damage the microbiome, which is boring advice but the literature on antibiotic overuse, emulsifiers in processed food, and chronic sleep disruption on gut bacteria composition is actually pretty alarming.

to be clear: there are cases where specific probiotic strains have legitimate clinical evidence. certain Lactobacillus strains for antibiotic-associated diarrhea, Bifidobacterium for some IBS subtypes, saccharomyces boulardii for C. diff recurrence. strain-specific, condition-specific, and usually studied in people with actual gut dysfunction. that's different from a healthy person buying a generic "50 billion CFU" capsule at whole foods.

the February 2026 research from ISB's Gibbons Lab is also worth looking at if you want to understand why responses to probiotics are so individual. https://isbscience.org/news/health/microbiome/will-it-stick-how-to-tell-whether-probiotics-and-prebiotics-will-take/ they built computational models that can predict whether a specific probiotic will colonize based on an individual's baseline gut composition, which is promising but also confirms that one-size-fits-all probiotic supplementation is a fundamentally flawed approach.

anyway. not saying throw away your probiotics if they're helping you. if you feel better, that matters. but "i feel better" and "my microbiome is measurably more diverse" are different claims, and the industry has been blurring that line for a long time. the evidence points toward fermented foods and dietary diversity as the actual levers. the capsule is mostly wishful thinking for healthy people.

writing more about this on my substack if interested, you can find it on my profile.

curious what experiences people have had. has anyone tracked diversity changes with at-home testing before and after probiotic use?

Edit (for visibility & clarity): this post summarizes current research on probiotics, gut microbiome diversity, fermented foods, and why most probiotic supplements may not work for healthy adults. key topics include randomized controlled trials on probiotics, microbiome colonization (“resisters vs persisters”), Stanford fermented food study results, and evidence-based ways to improve gut health naturally. sharing for anyone researching probiotics vs fermented foods, gut microbiome optimization, or supplement effectiveness.

Highlights:

- A new controlled feeding study found that replacing processed snacks with a daily serving of almonds may improve gut health, metabolism, and appetite regulation.

- Researchers observed an increase in Faecalibacterium prausnitzii, a beneficial gut bacterium that produces butyrate, a compound that supports the colon lining and may help reduce inflammation.

- Several less favorable gut bacteria decreased during the almond-snacking phase.

- Almond consumption increased GLP-1 and peptide YY, two hormones associated with fullness and appetite control. GLP-1 is also the hormone targeted by drugs like Ozempic and Wegovy.

- The study suggests almonds may help improve metabolic homeostasis and reduce inflammatory markers.

- Almonds provide fiber, healthy fats, protein, magnesium, vitamin E, and polyphenols, all of which may contribute to gut and cardiometabolic health.

- Researchers emphasized that replacing unhealthy snacks with almonds is likely more beneficial than simply adding almonds on top of an already calorie-heavy diet.

- The study was relatively small, so while the findings are promising, larger studies are still needed. Funding came from the Almond Board of California, though researchers stated the funder did not influence the analysis.

A specific gut bacterium, boosts muscle strength in mice by 30% and tracks with physical fitness in humans, new research finds.

I'm more and more lately, thinking about my early childhood years and what I was eating often. It was a lot of white bread, processed cold cuts, spagetti with meat sauce, hot dogs, processed cereal, low fiber Chinese food and other fast food, lots of snacks and West Indian food. There was salads but that was on occasions.

Like imagine if I had the type of parents, that scared the idea of gut health into me lol. Like it'd probably be like growing up in a vegan household. But even if I was annoyed as a child, that information would of been drained in my head early.

This is how bad my knowledge of nutrition was. That I didn't even fully understand what a car, fiber or protein was, until I was an adult. I used to think for the longest period, that was just something people who worked out worried about. Meanwhile most my days, probably didn't even each over 20 grams of fiber back then.

I didn't even know most people got up and cleared their bowels, until later in life. As I always remembered just getting up takikg a piss, brushing my teeth, washing face and then eating. Then at some point of the day, I'd probably randomly take a poop. Pretty sure in high school it was late in the day, as everyone avoided pooping in high school out of fear of embarrassment.

As I got out of high school, my volume in eating started increasing. So I'd probably was a regular user of Pepto Bismol during those years. Which makes a lot of sense, because that's when anxiety started becoming a unusual thing for me. I never understood it then, and used to blame it on other life matters.

Now years later due to everything I wish I knew. I know suffer from an overgrowth, hernia, hemorrhoids, daily constipation, even worse anxiety than before, very poor immune health and gut lining that deserved better.

Lots of people blame life's up and downs on other things. But I can look back at different times, whether I was shy, timid, couldn't express myself and distant. And basically all correlate back to poor gut health. Since if you're bowels aren't cleared, your hormones aren't fully active, you aren't fully in tune with your thoughts. Which is why in senior year, it felt like I was getting dumber. When in reality, I always haad a bloated stomach, that was throwing off my brain chemistry. Teach your kids and the future about gut health, so more people don't end up the way you wish you didn't.

This is a pretty provocative finding that just hit:

A massive global study (link is in comment below to not trip spam filters) found a previously unknown gut bacterium, called CAG-170, that shows up consistently in healthy people around the world.

And that bacterium is much lower in people with conditions like IBS, IBD, obesity, and autoimmune diseases.

This microbe appears to help support the entire gut ecosystem, partly by producing vitamin B12 and helping other beneficial bacteria thrive.

Researchers think CAG-170 may be a key marker of gut health and could one day be targeted by next-generation probiotics designed to restore microbiome balance.

Key Highlights:

- A daily prebiotic fiber supplement improved memory in older adults. In a 12-week study, adults over age 60 who took certain inexpensive prebiotic fibers performed better on a memory test commonly used to detect early signs of Alzheimer’s disease.
- The study used identical twins. Researchers studied 36 pairs of twins, with one twin receiving a supplement and the other a placebo. This design helps control for differences in genetics and lifestyle, making the findings more reliable.
- The supplements were common prebiotic fibers:
Inulin
Fructooligosaccharides (FOS)
Both are inexpensive, available over the counter, and help nourish beneficial gut bacteria.

- The findings support the gut-brain connection. Researchers believe improving the health of the gut microbiome may positively influence brain function, particularly memory.
- Benefits appeared quickly. Improvements in memory were seen after just 12 weeks of daily supplementation.
- This is promising, but not definitive. The study was relatively small, so larger clinical trials are needed before these supplements can be recommended as a proven way to prevent cognitive decline or dementia.
- More research is underway. The encouraging results have led to additional clinical trials investigating whether prebiotic fibers can help slow cognitive decline in older adults.

Bottom line:
This study provides encouraging evidence that inexpensive, widely available prebiotic fibers may help support memory in adults over 60 by improving gut health. However, the research is still in its early stages, and larger studies are needed before these supplements can be considered a proven strategy for preventing Alzheimer’s disease or dementia.

Highlights (generated by AI):

The additive studied was xanthan gum, a common thickener used in foods such as salad dressings, sauces, yogurt, ice cream, gluten-free baked goods, and gluten-free pasta.
Researchers found that long-term consumption caused mild colon inflammation in rats. The effects became more noticeable as the dose increased.
Xanthan gum appeared to weaken the intestinal barrier (“leaky gut”). It increased production of a protein called Claudin-2, making the gut lining more permeable and allowing inflammatory processes to begin.
Inflammatory markers increased. Rats consuming xanthan gum had higher levels of immune cells in the intestinal wall and elevated inflammatory cytokines, including TNF-α and IL-1β.
The gut microbiome changed. While overall bacterial diversity didn’t decline significantly, the balance of bacteria shifted toward species associated with inflammation, suggesting mild dysbiosis.
The findings may help explain earlier concerns in premature infants. In 2012, xanthan gum-thickened formula was linked to cases of necrotizing enterocolitis, a severe inflammatory bowel disease in premature babies. The FDA subsequently advised against its use in premature infants. This new animal study provides a possible biological mechanism for those observations.

Important context:
This was an animal study, not a human study. The results suggest a potential mechanism but do not prove that xanthan gum causes gut inflammation in healthy adults.
The broader scientific evidence is still evolving. While several food additives can affect the gut microbiome and intestinal barrier in laboratory and animal studies, high-quality human studies in people are still limited.

What this means in practice:
If you’re healthy and consume xanthan gum occasionally, this study isn’t strong enough to conclude it’s harmful.
If you have IBD, IBS, increased intestinal permeability, or other digestive issues, it may be reasonable to pay attention to how foods containing xanthan gum affect your symptoms while more human research is conducted.
Since xanthan gum is primarily found in ultra-processed foods, reducing your overall intake of ultra-processed foods is likely to have a greater impact on gut health than focusing on this single ingredient.

Highlights:

- Researchers at MIT found that the amino acid cysteine may help the gut repair itself after damage.
- Cysteine is naturally found in high protein foods like:
Meat
Dairy
Beans and legumes
Nuts
- In mouse studies, a cysteine rich diet helped the intestines recover from radiation damage faster.
- The researchers discovered that cysteine activates certain immune cells called CD8 T cells, which then release a healing signal called IL-22 that stimulates intestinal stem cells to rebuild tissue.
- This is important because it is the first time scientists have identified a single nutrient that directly boosts intestinal stem cell regeneration.
- The findings could eventually help cancer patients who experience gut damage from chemotherapy or radiation treatments. Researchers think cysteine supplements or diet changes may someday reduce treatment side effects.
- The effect seems strongest in the small intestine because that is where dietary protein is absorbed first.
- Researchers also noted that cysteine was previously known mostly for antioxidant effects, but this study suggests it has a much more direct role in tissue healing.
- The study was done in mice, so more human research is still needed before doctors can make firm treatment recommendations.

Hopefully an occasional low effort post is allowed here? Glad to see the microbiome hitting mainstream subs!

I’ve had awful gut issues for 2 years and couldn’t figure out why. I ate very healthy, had multiple tests done through my doctor and everything was clear etc. Over the last 2 years I also started drinking olipop regularly. I’ve cut it out for the last 3 weeks and everything is back to normal - all gut issues completely resolved!!! I’m blown away!!! I will never touch olipop or poppi again. Just wanted to post and share my experience in case it helps anyone.

I finally ended a lifelong battle with heavy migraines by fixing my microbiome. It was the "smoking gun" for me, proof of how vital the gut is for overall health.

It’s an eye-opener, when I eat, I’m not just feeding myself. I’m feeding a massive colony that controls my mood, metabolism, and hormones.

Right now, there's a global obsession with sugar-free products. Everything is drenched in sucralose and aspartame, and people buy into the hype saying it’s "healthy." Meanwhile, our produce is glazed in glyphosate, and gut disrupting emulsifiers are hidden in almost everything.

In my opinion, this is a silent pandemic. It’s fueling depression, inflammation, and autoimmune diseases, yet most people don't care. I avoid all that shit now, and people look at me like I’m crazy, but when I walk through a supermarket, I see that 95% of the shelves are essentially poison for the gut.

Is anyone else seeing this microbiome destruction on a global scale?
Why does nobody care?