Worst Foods for Gut Health

Certain foods are proven enemies of gut health. Yet we seem only to read articles and books, see YouTube videos and nutrition influencers telling us what we should eat to keep our gut microbiome in check.

We’re here to correct that imbalance with a complete guide to the foods and drinks to avoid if you want to maximise the wellbeing of that beautiful microbiome.

Food And Your Gut Health

Why is what you eat so important to gut health? And how does gut health impact whole body wellbeing?

How what you eat affects your gut’s health

A healthy diet is essential for good gut health^[i]. Not only does your diet provide nutrients essential for energy, immunity and all-round health, it also provides food for the microbiome, the microscopic world that lives inside your intestinal tract.

What we consume affects the structure, function and composition of the gut microbiome. And as important as getting those nutrient-rich whole foods into your gut? Keeping harmful substances out.

Gut health, IBS and other gastrointestinal problems

The health of your gut microbiome can be reflected in the wellness of your gastrointestinal tract. Dysbiosis is the term used for an imbalance in the microbiome, and it often shows itself as:

Diarrhoea
Constipation
Bloating
Gas
Nausea
Cramping

Additionally, dysbiosis has strong links to long term gastrointestinal issues, including IBS^[ii], IBD^[iii] and Crohn’s disease^[iv].

Why gut health is so important for your wellbeing

Your gut is linked to almost every aspect of your health, including:

Immunity: around 70% of your immune system is based in your gut^[v]. Here, immune cells learn to fight infection and inflammation is combated. A physical barrier also defends against pathogens^[vi]
Mental wellbeing: the gut-brain axis is a two-way physical and chemical connection between brain and intestinal tract^[vii]. Research shows a link between gut health, stress, anxiety and depression^[viii]. Gut bacteria has even been linked to personality^[ix]
Weight: experts think that the gut microbiome could affect our propensity towards obesity^[x]
Disease: numerous studies link the state of intestinal microbiota to significant issues, including respiratory and cardiovascular diseases^[xi]
Fertility: research shows that gut health plays an important role in fertility and embryo development^[xii]
Allergies: emerging research proves a strong link between gut dysbiosis and allergies^[xiii], including hayfever^[xiv]

The Worst Foods for Gut Health

Some foods are better than others when it comes to keeping your gut in A-one condition. Meanwhile, some foods wreck real havoc on your gastrointestinal wellness...

What ultra-processed foods do to your gut

Ultra-processed foods (UPFs) are proven to be a total disaster for your gut^[xv]. Low in nutrients such as fibre, and packed with additives intended to lengthen shelf lives and boost flavour, these convenient and often far too delicious foods are finally under fire for their negative impact on health.

Specific to the gut, a diet full of UPFs can disrupt the balance of your gut flora, create an environment prone to inflammation and increase intestinal permeability^[xvi]. The result? Research points to worsened gastrointestinal, metabolic and neuropsychiatric outcomes and a higher risk of gastrointestinal diseases^[xvii].

7 worst foods for gut health

Fried, fatty foods: diets high in saturated fat have been linked to modification of the microbiota. This leads to dysbiosis, inflammation and an increase in leaky gut (porosity in the gut lining, providing access to nasties including bacteria and toxins)^[xviii]
High-sugar foods: consuming too much sugar, and especially refined sugar, can lead to reduced microbial diversity^[xix]. This diversity is essential for good gut health^[xx]
Alcohol: a high intake of alcohol is associated with poor all-round health outcomes. It’s no surprise then that booze is seen to damage the microbiome too, affecting the composition of bacteria and increasing gut permeability^[xxi]
Artificial sweeteners: though sweeteners are touted as a useful tool in weight management, they can also be a damaging choice. Trials suggest they could be responsible for changes to microbiota, resulting in impaired glycemic tolerance^[xxii]
Refined grain: for good gastrointestinal health look to whole grains, which are packed with gut-supporting fibre, over fibre-lacking refined grains
Red meat: eating too much red meat, especially if highly processed, could cause damage to the gut. Early studies link excess consumption to disruption of the gut and exacerbation of existing disorders^[xxiii]
Foods that make you feel... not quite right: listen to what your body’s telling you! Bloating after bread? Could be a wheat intolerance. Dairy diarrhoea? Maybe milk isn’t for you. Sensitivities and their symptoms could fuel gut imbalance^[xxiv]. Be sure, however, to consult your GP if you suspect an allergy or intolerance

Optimising Your Diet for Better Gut Health

Ready to get your gut into the best shape of its life? It’s as much about what you do as what you don’t...

The psychology of processed foods

Ultra-processed foods are a hard habit to kick. Not only are UPFs usually easier to get hold of and prepare, they’re often cheaper too. But the most cunning part of your favourite fake food? It’s designed to keep you coming back for more.

UPFs are often, sadly, our idea of a treat. Packed with craving-sating salt and sugars they’re usually the thing we choose when we need a pick-me-up, can’t be bothered to cook or have a craving that needs to be satisfied. Psychologically, UPFs are built to feed our reward system with everything from packaging to nutrient density to flavour enhancers, influencing the reward centres in our brain^[xxv].

With this in mind it’s easy to see why experts are now comparing UPFs to cigarettes in terms of their health risks^[xxvi].

How to stop eating ultra-processed foods (UPFs)

Giving up UPFs requires more than willpower:

Go cold turkey: UPFs feed your cravings, so one processed ‘treat’ only leads to another
Eat breakfast: if you skip breakfast, you’re more likely to seek out a cheeky 11 am snack when hunger hits
Get organised: meal prepping/planning and shopping ahead reduces the likelihood of a last-minute takeaway or ready meal
Find ‘good’ treats: pack your bag or office drawer with delicious whole food treats to answer the 4 pm sugar craving call
Forgive yourself: don’t let that one slip up be your downfall. Accept that you fell off the UPF-free wagon and hop back on board asap, ready to fight another day
Recognise the wins: less bloated? Better bowel movements? Skin looking brighter? Feeling less sluggish? Celebrate every positive outcome as a reminder of why you’ve ditched UPFs for good

Easy gut health hacks

There’s plenty you can do to improve your gut health without a complete diet overhaul:

Add fibre: dietary fibre is essential for the production of microbial metabolites, feeding your good bacteria^[xxvii]. It’s worth noting that prebiotic fibre in legumes, wheat and onions, among others, is considered more beneficial than, for example, that found in potatoes, rice and fruit^[xxviii].

Hydrate: drinking plentiful water is a must for the microbiome. Helping to break down food and ensure a smooth journey through the intestinal tract. Conversely, lack of hydration is implicated in reduced diversity in the microbiome^[xxix]

Eat fermented: the gut loves fermented foods. Studies confirm that ‘good’ bacteria in kimchi, tofu, sauerkraut and more can reach the gut intact for improved diversity^[xxx]

Go probiotic: a regular probiotic supplement is a reliable way to support gut health with none of the guess work. Choose a quality one-a-day supplement from PrecisionBiotics for better digestive health

Summary

Diet is absolutely crucial to the health of your all-important gut microbiome. And what you leave out is just as important as what you put in. Ditch those ultra-processed foods to protect your intestinal health and opt instead for wholesome, hearty whole foods. Keeping your intake of alcohol, refined sugars, red meat and saturated fats low while upping your intake of fibre and water is a must too.

Sources:

[i] https://pmc.ncbi.nlm.nih.gov/articles/PMC9455721/

[ii] https://pmc.ncbi.nlm.nih.gov/articles/PMC10609453/

[iii] https://pmc.ncbi.nlm.nih.gov/articles/PMC8998182/

[iv] https://pmc.ncbi.nlm.nih.gov/articles/PMC8320851/

[v] https://www.sciencedirect.com/science/article/pii/S0896841123001233

[vi] https://pmc.ncbi.nlm.nih.gov/articles/PMC8001875/

[vii] https://pmc.ncbi.nlm.nih.gov/articles/PMC10384867/

[viii] https://www.nature.com/articles/s41598-025-86858-3

[ix] https://www.ox.ac.uk/news/2020-01-23-gut-bacteria-linked-personality

[x] https://pmc.ncbi.nlm.nih.gov/articles/PMC8291023/

[xi] https://www.nature.com/articles/s41392-022-00974-4