what is ‘gut health’ and what role does diet play?

(my mom makes homemade kimchi!! carrying a piece of korea with us :,))

in the last few years, “gut health” has exploded in popularity within the wellness space  - and rightly so! it’s illuminating to understand something so intrinsically tied to everything from mental health, immune function and chronic disease.

that being said, it has also attracted a lot of pseudo-sciencey rhetoric (we've all seen the ‘gut health’ gummies or whatever on tik tok). ‘gut health’ has become somewhat stripped of meaning, getting lumped in with vague concepts like “hormone-balancing” or “detoxing” - although they may sound compelling, they aren’t particularly accurate from a scientific standpoint.

so let’s slow it down and get specific! 

your gut refers primarily to the gastrointestinal tract; gut health describes how well this system digests food, absorbs nutrients, maintains barrier integrity and interacts with the immune and nervous systems. central to this is the gut microbiome - the trillions of bacteria, viruses and fungi living in your intestines. a “healthy” gut is marked by its diversity, resilience and overall balance. functionally, that looks like regular bowel movements, minimal bloating or discomfort, stable energy and an immune system that isn’t constantly on edge.

diet is one of the strongest modulators of the microbiome - it impacts which microbes thrive, which fade and how they interact with your body over time! with that in mind, here’s a practical way to think about grocery shopping for gut health, grounded in established biological mechanisms!

microbiome builders: foods that increase microbial diversity over time

(more variety in food = more diverse substrates = attracts a wider range of specialised microbes!)

one of the most consistent findings in gut research is that greater microbial diversity is associated with better health outcomes. foods that provide a wide range of complex carbohydrates and plant compounds create more “substrates” for different microbes to specialise in breaking down. simply put: more variety in food equals more variety in microbes.

these foods help support microbial diversity and regular digestion:

• lentils, chickpeas, black beans and kidney beans

• oats and barley

• apples and pears (with skin)

• berries (especially raspberries)

• broccoli, brussels sprouts and carrots

• nuts and seeds (chia, flaxseed, almonds, walnuts)

contrary to popular belief, fiber doesn’t “clean you out” per se. it provides structure, slows digestion (where needed) and supports microbial metabolism - laying the groundwork for a more resilient gut ecosystem over time.

fermentation fuel: foods that microbes ferment into beneficial compounds

(this plate of food i had in tanzania lives in my head RENT-FREE!!)

not all fibers function the same way. some carbohydrates resist digestion in the small intestine and reach the colon intact, where gut microbes ferment them into short-chain fatty acids (scfas) like butyrate. these compounds play a key role in gut lining integrity, immune regulation and inflammation control.

foods rich in resistant starches and fermentable fibers include:

• oats

• beans and lentils

• green (underripe) bananas

• cooked and cooled rice

• cooked and cooled potatoes

• whole grains

• onions and garlic

as with most things gut-related: quantity and pacing matter - introducing fermentable fibers gradually helps minimise bloating and discomfort while allowing microbes to adapt.

gut barrier supporters: foods that help maintain the intestinal lining

(probably my favorite category HEHE ~ a girl who loves salmon with all her heart!)

gut health isn’t only about microbes; it’s also about the intestinal barrier, a selectively-permeable lining that determines what passes from the gut into the bloodstream. a compromised barrier can contribute to inflammation and immune dysregulation.

certain foods provide nutrients involved in mucus production, tight junction integrity and anti-inflammatory signaling:

• extra virgin olive oil

• fatty fish (salmon, sardines)

• eggs

• bone broth or collagen-containing foods

• yogurt and kefir

• cooked root vegetables (sweet potatoes, squash)

for people with sensitive digestion: preparation matters. cooking, peeling and softening foods can significantly improve tolerance without meaningfully reducing nutritional value.

polyphenol-rich plants: foods that selectively nourish beneficial microbes

(i think it's sooo fascinating how they modulate which microbes gain an advantage, shaping gut composition! the human body never ceases to amaze!!)

polyphenols are plant compounds with antioxidant and anti-inflammatory properties - but many of them aren’t fully absorbed by the human body. instead, they interact directly with gut bacteria, acting as microbial modulators that can increase beneficial strains while suppressing opportunistic ones.

polyphenol-rich foods worth including:

• blueberries and other dark berries

• pomegranate

• red cabbage

• extra virgin olive oil

• green tea and coffee

• dark chocolate (70%+)

• herbs and spices (turmeric, cinnamon)

these foods don’t just add diversity - they shape which microbes gain an advantage, subtly influencing gut composition over time.

live microbe foods: foods that help support the gut environment

(tempeh is a newer addition in our household but it goes crazy with some chili oil!)

fermented foods contain live microorganisms delivered within a food matrix, which may enhance their survival through digestion compared to isolated supplements.

examples include:

• yogurt with live cultures

• kefir

• sauerkraut

• kimchi

• miso

• tempeh

• fermented pickles (true fermented, not vinegar-based)

it’s important to be clear here: fermented foods don’t permanently colonise or “reseed” the gut microbiome on their own. their effects are transient - but when eaten regularly, they can meaningfully influence microbial activity and gut function.

a final note on “gut-friendly” eating

(this education is SO important, especially for those of us who might've previously only understood nutrition through 'macros' - there's so much more to the picture!)

there is no universally perfect ‘gut diet.’ genetics, stress, sleep, medications and prior dietary patterns all shape how your gut responds to food!

what matters most is consistency, diversity and tolerance - rather than rigid rules, fear-based elimination (unless medically-necessary) or chasing single “superfoods.” a gut-healthy grocery list is about building a food environment that supports microbial diversity, digestive function and long-term resilience.

small, repeatable choices - made week after week - are where it’s at!

builtwithhabit.

~

if you liked this post and want to read more about what non-performative wellness looks like, then please check out these other blogs i’ve written!

food as medicine

beyond fad diets

food across borders