While “there are other food additives that are lesser players,” she says, those are the “big ones that we know significantly alter the gut microbiome and increase inflammation” — a state that can induce harmful changes in the resident microorganisms and increase the risk of disease. Specifically, Dr. Burkhart explains, they “make the gut more permeable and harm the mucosal lining,” the protective layer of cells that coats the inside of the intestine, allowing pathogens in and potentially setting the stage for infection. To prevent these harmful changes, try to minimise your processed food intake. “Eat more whole grains, eat more real food, plants, fruits, vegetables, legumes, those types of things,” Dr. Burkhart says. (Which is not to say that you can or should never enjoy processed products, of course — just that they should be enjoyed sparingly rather than regularly.)

3. Guzzling sugary beverages

“Consuming a lot of sugary foods or drinks decreases diversity, increases inflammation and increases [gut barrier] permeability,” Dr. Burkhart says — none of which you want, as we’ve covered. Reduced diversity, for example, can manifest as a decline in one type of bacteria, Bacteroidetes, and an uptick in another, Proteobacteria —a pattern often associated with dysbiosis and resulting health conditions. Because of this, Dr. Burkhart recommends limiting stuff like fizzy drinks and sweet fruit juices and replacing them with water or another unsweetened beverage if you’re thirsty.

4. Not eating enough fibre…

By far the most substantial dietary change that you can make for your gut microbiome is eating more fibre, according to Nielsen. Consider it “almost like a medicine,” Dr. Burkhart says. Why? Well, a high fibre intake supports beneficial bacteria — the ones that help to “improve gut barrier function, communicate with the immune system, and keep chronic inflammation at bay” — since fibre is their primary food source, Nielsen explains.

By contrast, she says, cutting out fibre boosts harmful bacteria that tend to cause inflammation — hence why adopting an animal product-based carnivore diet à la influencers like Steak and Butter Gal or the Liver King is “the worst thing you can do for your microbiome.” In fact, fibre is so critical that even though whole foods are always a better option, Dr. Burkhart often recommends fibre supplements to people struggling to reach their daily fibre goal. Getting 30 to 50 grams per day is “really, really important for gut health,” she says.

5. …or drinking lots of prebiotic drinks in lieu of eating high-fibre foods

Prebiotic soda refers to a class of drinks that contain the namesake fibres, which, like their brethren, feed the microbes in your gut and stimulate the growth of beneficial bacteria. Don’t get us wrong: “They’re amazing, and they offer a great boost, but they don’t function the same way as whole foods,” Nielsen says. Compared to prebiotic sodas, which often contain a specific prebiotic known as inulin but not much else, whole foods offer a much broader array of beneficial nutrients — including polyphenols. Found in plant foods like fruits and vegetables, these antioxidant and anti-inflammatory compounds may not be as well-known as fibre, but they play a big role in “driving the growth of a healthy microbiome, too,” Nielsen says. Fundamentally, this is a prime example of the importance of diversity: Sweet and tangy as those drinks may be, they’re pretty one-note. When it comes to your fibre fix, fruits and veggies are a way better bet.

6. Steering clear of foods that cause digestive side effects

“There’s a lot of really bad advice out there that if certain foods — say, legumes, for example — cause a symptom, that means you’re intolerant to them and shouldn’t eat them for your gut health, when literally the opposite is true,” Nielsen says. It all comes down to the fibre content. Most Americans are severely deficient in fibre and would thus benefit from eating fibre-rich foods like legumes more often, but increasing your fibre intake all at once can initially cause the exact digestive issues it’s supposed to prevent — gas, bloating, diarrhoea — since your body isn’t prepared for the higher load. So rather than signalling that you have an intolerance toward a specific food, these symptoms are actually “a sign that you need to double down and actually consume more of those things,” Nielsen says. But GI issues aren’t an inevitability: Starting slow with “consistent, small amounts” can help minimise your chances of tummy trouble.

7. Going too hard on probiotic supplements…

On the surface, taking a probiotic supplement — a pill, capsule, powder or gummy packed with beneficial microbes, including bacteria and yeasts — might seem like a no-brainer strategy for boosting your gut microbiome. Per Nielsen, however, not all probiotics are equal in efficacy, and not all even target the same site (or health issue), so they won’t necessarily have the effects you think they will.