u/thelostdutchman68

Took longer to pull this one together than expected. Work plus caring for my 97 year old dad has eaten my evenings. 😊

The response to the first two posts has been overwhelming. Thank you for the comments, questions, and the willingness to dig into this stuff with me. Honestly didn't think a list of fruits would reach the numbers it did.

Quick note before we get into it: check the first two posts if you missed them, especially if you've got SIBO, IBS, FODMAP issues, or other active GI stuff. If you're in an active flare or under medical supervision, take it slow with new foods. Always.

Fruit and veg feed the bacteria up front, in the early colon. That work matters. You want both in your diet. But they don't reach everywhere.

The descending colon, where most colorectal cancers happen, runs on different fuel. The bacteria there make butyrate, which your colon cells actually prefer over glucose for energy. Those bacteria need slow fermenting substrate that survives the trip through the upper gut intact.

That's where beans and tubers come in. Not as a backup. As the foods that feed a region of your gut other fibers can't.

Beans are the magical fruit (had to work that in somewhere). They bring galactooligosaccharides (GOS). It's a prebiotic that specifically feeds Bifidobacterium. Bonus points if you can pronounce galactooligosaccharide. Bigger bonus if you can spell it without looking. Beans also bring resistant starch, which slows fermentation down and pushes some of the work deeper into the colon.

Tubers are the most concentrated source of resistant starch in the diet. Sweet potato, white potato, yam, cassava, taro. The trick is cooking them and then cooling them. That process turns regular starch into Type 3 resistant starch, which slips past the small intestine and arrives in the descending colon where the butyrate makers can ferment it.

Butyrate matters. Preferred fuel for your colon cells. Anti inflammatory. Supports the gut barrier. Associated with reduced colorectal cancer risk. The bacteria that make it (Faecalibacterium, Roseburia, Eubacterium) live in the descending colon. They need slow fermenting substrate to do their job. No substrate, no butyrate.

Together, beans and tubers cover the slow fermentation zone that fruit and veg can't reach. Beans actually hit two zones at once because of the GOS plus resistant starch combo. Tubers concentrate the slow work where butyrate matters most.

Here's the part that should reframe how you think about chronic disease.

The chronic disease epidemic isn't natural aging. It isn't genetics. It isn't bad luck. It's the predictable consequence of destroying the microbial ecosystem humans evolved with. Populations eating high carb, plant and tuber based diets have the lowest rates of cardiovascular disease and dementia ever documented in humans.

That conclusion is uncomfortable. It's also what the data shows. The diseases we treat as inevitable consequences of getting old are mostly consequences of how we eat.

Tubers & Root Vegetables
Lentils (M)
Chickpeas (M)
Black beans (M)
Adzuki beans (M)
Fermented soybeans (M)
Kidney beans (M)
Pinto beans (M)
Mung beans (M)
Navy beans (M)
Split peas (M)

F = Fast fermenting (ascending colon) M = Medium fermenting (transverse colon) S = Slow fermenting (descending colon) *Disclaimer: there's logic to the list and the order, but a subjective element too. Ranked on microbiome health as the primary factor, with longevity and mortality, disease prevention, and practical accessibility factored in. If your fav. isn’t listed doesn’t mean it isn’t good to eat or healthy.  

Lentils are the gateway. They cook in 20 minutes with no soaking. Canned beans are fine. Drain and rinse to cut some of the oligosaccharides that cause initial gas. Reduced sodium where you can find it. Start with a quarter to half a cup daily and let your gut adjust over 2-3 weeks before bumping it up.

Tubers, roast, bake or boil a batch on the weekend. One potato side dish a day measurably shifts the microbiome. Gas tolerance ramps up. First 2-3 weeks you'll have more gas. The bacteria that ferment this stuff are expanding. By week three or four the gas drops off while the benefits keep going.

Cooking and cooling matters. Cooked and cooled starches (potatoes, sweet potatoes, rice, beans, lentils) form Type 3 resistant starch. That shifts the fermentation profile toward slow. Reheating preserves most of the resistant starch. You don't have to eat them cold.  You can heat them up and enjoy them nice and hot.   I love Korean sweet potatoes.  I bake a bunch on Sunday and let them chill in the fridge.  They make great snacks and work well cold in salads or heated up with a little bit of brown butter. 

The supplement industry can't sell you what beans and tubers deliver. You can't patent a sweet potato. You can't put GOS in a capsule and match what a cup of lentils does. The food matrix, the fiber diversity, the resistant starch, the slow release into the right region of the colon. None of it fits in a pill.

A $2 bag of lentils and a $4 bag of sweet potatoes outperforms any probiotic or prebiotic supplement on the market. Some of the most powerful microbiome food available, hiding in plain sight in your grocery store.

The last post in this series will be about fermented foods and these are the links to the first two posts in this series.

Fruit https://www.reddit.com/r/Microbiome/comments/1te005q/fruit_is_one_of_the_most_underrated_tools_for_gut/

Veg https://www.reddit.com/r/Microbiome/comments/1test0s/vegetables_are_the_most_underrated_tools_for_gut/

Sources:

Kaplan H, et al. (2017). Coronary atherosclerosis in indigenous South American Tsimane. The Lancet. Link

Gatz M, et al. (2022). Prevalence of dementia in Bolivian forager-horticulturalists. Alzheimer's & Dementia. Link

Naghshi S, et al. (2023). Legume consumption and risk of all-cause and cause-specific mortality. Advances in Nutrition. Link

David LA, et al. (2014). Diet rapidly and reproducibly alters the human gut microbiome. Nature. Link

Davis LM, et al. (2011). Consumption of GOS Results in a Highly Specific Bifidogenic Response in Humans. PLoS One. Link

*DeMartino P & Cockburn DW (2020). Resistant Starch: Impact on the Gut Microbiome and Health. Current Opinion in Biotechnology. https://www.sciencedirect.com/science/article/abs/pii/S0958166919301077

Link corrected. :)

Vegetables are the foundation of microbiome diversity, and most of us aren't eating enough variety.

Two things came up in the comments on the fruit post that need addressing before we dig into vegetables.  See: Fruit is one of the most underrated tools for gut microbiome diversity.

If fruit had probiotic capsules as the industry workaround, vegetables have greens powders. You know the brands and have seen the advertising. Same playbook. They position them as "vegetable replacements" for people who don't eat enough actual vegetables. The reality is that $50 to $80 a month for processed powder buys you significantly less than $20 a month buys you in actual vegetables. Real vegetables bring fiber, water content, live enzymes, intact polyphenols, and the food matrix that protects nutrients through digestion. Powders are dehydrated, processed, and often heat damaged versions of those same compounds. Your gut doesn't want a supplement. It wants food.

Second, the FODMAP and SIBO question. The vegetable list includes several high FODMAP items (garlic, onions, leeks, asparagus, brussels sprouts, cabbage, cauliflower, broccoli). For someone with active SIBO, fructose malabsorption, or significant gut dysbiosis, this list isn't the right starting point. I strongly encourage you to address the underlying imbalance first, then reintroduce these foods slowly. The list applies to people who are otherwise healthy and who are trying to build microbiome diversity, not to people in active GI flare.

Let's be honest with ourselves. While we may eat a decent amount of vegetables, there isn't much variety. Potatoes (as fries), tomatoes (as sauce and ketchup), onions, lettuce, and corn account for the majority of vegetable consumption in N.A. The fruit post talked about diversity. Vegetables are where the diversity problem is even more pronounced. The good news is that vegetables also offer the widest possible range of microbiome inputs of any food category. Vegetables do everything fruit does plus several things fruit doesn’t.

Why this matters. Microbiome diversity is the strongest predictor of microbiome health, and dietary diversity is the strongest predictor of microbiome diversity. The American Gut Project (McDonald 2018) found people eating 30+ different plant species per week had measurably more diverse microbiomes than those eating fewer than 10. More diverse microbiomes are consistently associated with better metabolic markers, lower systemic inflammation, stronger gut barrier function, and reduced risk of cardiovascular disease, type 2 diabetes, inflammatory bowel disease, depression, anxiety, and colorectal cancer. Low microbiome diversity shows up in nearly every chronic disease that's increased over the last 50 years. Let that sink in for a moment.

Different bacteria specialize in different fibers and polyphenols. Eating the same five vegetables every day, feeds the same handful of bacterial species. Rotating through 15-20 different plant sources across a week feeds a much wider range. The diversity you eat becomes the diversity you build, and that diversity is what protects you. 

This is vegetables only. Next up in the series: legumes (the magical fruit), then fermented foods, nuts and seeds, mushrooms, and the rest. The integrated diversity across all categories is what builds the microbiome the research keeps pointing to.

I did some simple research and here is my vegetable list, ranked most beneficial down for microbiome support, with fermentation speed indicated.

The ranking is based on four criteria: prebiotic fiber content (inulin, FOS, GOS, pectin, arabinoxylan, resistant starch), polyphenol density and diversity (anthocyanins, sulforaphane, quercetin, kaempferol, and others), specific bacterial population support (which beneficial species each vegetable feeds), and documented research base for microbiome effects. Vegetables high in inulin and other fast-fermenting fibers cluster at the top because they have the strongest direct prebiotic effect. Cruciferous vegetables follow because of their unique sulforaphane and glucosinolate contributions. Polyphenol-rich and leafy greens round out the list based on overall microbiome impact rather than any single mechanism.

The fermentation speed indicates where in the colon each vegetable fiber gets broken down. Fast in the ascending colon (early). Medium in the transverse colon (middle). Slow in the descending colon (end). The point is to combine vegetables across all three speeds within meals so different bacterial populations get fed simultaneously, and to rotate the specific items across days and weeks to build broader diversity over time. Both matter.

1. Jerusalem artichoke (sunchoke): fast
2. Garlic: fast
3. Globe artichoke: fast
4. Leeks: fast
5. Onions: fast
6. Asparagus: fast
7. Dandelion greens: fast
8. Endive: fast
9. Fennel: fast/medium
10. Cabbage (especially fermented as sauerkraut or kimchi): medium
11. Brussels sprouts: medium
12. Broccoli: medium
13. Kale: medium
14. Cauliflower: medium
15. Bok choy: medium

A note on the top of the list. The first nine vegetables are fast fermenters because they're rich in inulin. They're also the most likely to cause gas if you've been on a low-fiber diet. If that's you, start lower on the list with the cruciferous vegetables and leafy greens, then add the fast fermenters gradually over a few weeks or months. Seriously - start slow. It takes your gut time to adapt to new foods. While we can have a good giggle about fart jokes, but gas and bloating can be uncomfortable, on both sides, if you get my meaning.

A note on dandelion greens and endive. These are unfamiliar to most American eaters but they're some of the most concentrated sources of inulin in the vegetable world. Available at farmers markets and Mediterranean grocers. The bitterness moderates significantly when sautéed with garlic and olive oil.

Practical suggestions: Combine vegetables across the fermentation speed range within meals so different bacterial populations get fed simultaneously. Rotate the specific vegetables across days for broader diversity. Cook some, eat some raw, both have value. Frozen is fine. Prioritize organic for leafy greens and bell peppers.

Link to the Fruit Post. https://www.reddit.com/r/Microbiome/comments/1te005q/comment/om5tt4n/

Sources: 

McDonald 2018 mSystems - PMID 29795809, DOI 10.1128/mSystems.00031-18, volume 3 issue 3, e00031-18.

Calatayud 2021 Frontiers in Nutrition - DOI 10.3389/fnut.2021.700571.

Gill 2021 Nature Reviews Gastroenterology & Hepatology - 18(2):101-116, DOI 10.1038/s41575-020-00375-4, PMID 33208922.

Longtime lurker and commenter. This is my first post y'all so go gentle please.

I keep seeing posts here about which probiotic supplement to take, which is fine if you have a specific issue.

The reality is that most people don't have a probiotic deficiency. They have a fiber and polyphenol deficiency. Your existing microbiome is sitting there waiting to be fed, and you're throwing $50 a month at capsules instead of using that money on food. Probiotics introduce new bacteria. Prebiotics feed the bacteria you already have. The order matters. Feed what's there first. The supplement industry doesn't lead with this because food doesn't have the margins capsules do.

I did some simple research and here is my fruit list, ranked most beneficial down for microbiome support, with fermentation speed. There are clearly other criteria you could use to rank, but this is a microbiome post. :). NOTE - this list goes from most beneficial at 1. The further down the list the less beneficial. I cut things off at 15 choices.

1. Berries (blueberries, raspberries, blackberries): fast
2. Pomegranate: med
3. Strawberries: fast
4. Apples (with skin): fast
5. Kiwi: Fast/med
6. Tart cherries: med
7. Avocado: slow
8. Pears: fast
9. Persimmons: med
10. Oranges (with pith): fast
11. Prunes:med
12. Blackcurrants: fast
13. Figs (fresh or dried): fast
14. Plums: med
15. Grapefruit:fast

If you only eat fast fermenters, you're feeding the bacteria at the beginning while starving the ones at the end. The point is to feed the entire ecosystem, which means rotating across all three speeds. Keep in mind fast can lead to more gas...

Don't jump straight to the high inulin fruits if you've been on a low fiber diet. The gas and bloating is your bacteria recalibrating to new food, but it feels like the food is the problem. Start with the slow and medium fermenters then add the faster ones gradually over a few weeks to months. Your gut will catch up.

The American Gut Project (McDonald 2018, mSystems) found people eating 30+ different plant species per week had significantly more diverse microbiomes than those eating fewer than 10. Fruit alone won't get you to 30, but it's a meaningful chunk. Aim for 5 to 7 different fruits per week from this list, rotating rather than eating the same one every day.

Practical suggestions: Eat the skin where edible (apples, pears, peaches). Most of the fiber and polyphenols live there. Eat citrus with the pith (the white stringy part). That's where the pectin is concentrated. Frozen is fine. Frozen berries are often nutritionally equivalent to fresh and significantly cheaper. Juice isn't fine for this. Hope some of y'all find this helpful.

Please note this post is intended to be educational and mostly applies to individuals who are otherwise relatively healthy and are trying to improve their microbiome and overall health. For anyone with active GI conditions like SIBO, the order of operations is different and "feed your microbiome" comes after "fix what is broken."

This is the link to the other post on Veg. https://www.reddit.com/r/Microbiome/comments/1test0s/vegetables_are_the_most_underrated_tools_for_gut/

Sources:

McDonald 2018 mSystems - PMID 29795809, DOI 10.1128/mSystems.00031-18, volume 3 issue 3, e00031-18.

Calatayud 2021 Frontiers in Nutrition - DOI 10.3389/fnut.2021.700571.

Gill 2021 Nature Reviews Gastroenterology & Hepatology - 18(2):101-116, DOI 10.1038/s41575-020-00375-4, PMID 33208922.