Move over football; the latest trend captivating the nation is all about ‘gut health.’ Once confined to niche health food stores, items like kefir, kombucha, kimchi, and sauerkraut are now readily available in mainstream supermarkets.

Recent studies have highlighted the critical role of the gut microbiome—the collection of bacteria residing in our intestines that aids in food digestion—in maintaining overall health. This newfound understanding has sparked widespread interest and attention.

Research suggests that a well-balanced gut can have far-reaching impacts, influencing everything from our immune system and metabolism to mental well-being.

Given these revelations, it’s no wonder discussions about gut health are at an all-time high. Notably, gastrointestinal symptoms account for one in every eight visits to general practitioners, and issues related to gut health are on the rise.

According to findings published by BMC Gastroenterology, there has been a 34 percent increase over the past decade in cases of inflammatory bowel diseases, including autoimmune conditions like Crohn’s disease and ulcerative colitis.

Furthermore, surveys indicate that up to half the population experiences acid reflux, while food intolerances are also becoming more prevalent.

But as important as it is to build good bacteria in the gut by eating foods full of healthy pro- and prebiotics, not eating certain foods can be just as important when building up the microbiome, say experts.

In fact, you may be surprised by just which foods can actually do the most damage to gut bacteria — and disrupt digestion more generally. 

So read on for our expert-led guide to the worst foods for your gut health… and what to swap them for.

Supermarket bread

It’s well known that ultra-processed foods — those high in fat, sugar, and usually wrapped in plastic — are bad for the gut. 

But there’s one family favourite in particular that still tends to slip under the radar, says gastrointestinal physiologist at the Microbiome Clinic Jordan Haworth.

‘A lot of supermarket breads are surprisingly bad for the gut due to their high content of synthetic emulsifiers,’ he explained. 

Emulsifiers, used to add bulk to food, are found in a range of popular products — from cakes to children’s yoghurts.

However, experts have suggested that emulsifiers can ‘mess up’ the separation between the fatty layer and water layer in the gut, leading to gaps in the protective gut lining.

This is thought to increase the risk of bacterial infections in the gut, some of which are known to trigger the development of bowel cancers.

And whilst natural emulsifiers — made from plants, and with names like lecithin, guar gum and pectin — are less bad for the gut, most supermarket breads are made with synthetic alternatives, as they better improve dough strength and freshness. 

White bread’s processing also removes fibre, which is crucial for feeding good gut bacteria and removing toxins, leading to poor microbial diversity, said Mr Haworth. 

‘As a result, supermarket loaves can replace whole grains in the diet, meaning you eat less fibre and more sugar, fat and additives like emulsifiers,’ he explained. 

‘It tends to be the big brands who are the worst culprits when it comes to pre-packaged bread.’  

But even supposedly gut healthy sourdough loaves from the supermarket have come under fire from nutritionists in recent months. 

Renowned nutrition scientist Professor Tim Spector, founder of the popular Zoe diet app, took to Instagram last year to warn followers against buying ‘healthy’ sourdough breads when doing their supermarket shop. 

Prof Spector said many supermarket loaves are labelled ‘sourdough’ to ‘fool’ us into thinking they are healthy.

Some products may also use terms such as ‘high fibre’, he added. However these claims are nothing but a ‘health halo’.

In fact, these breads contain ‘several chemicals to including commercial yeasts, flavourings and emulsifiers to imitate the taste of real sourdough in far less time’.

To be safe, says Mr Haworth, get your bread from your local bakery — or check the nutrition labels for nasty additives and always buy the multi-grain option. 

Ice cream 

We’ve all experienced the awful stomach-ache that can come with eating too much ice cream. 

But it’s not just the richness — and copious amounts of sugar — in the popular dessert that can damage the gut, says GI physio Jordan Haworth. 

‘Ice creams are also full of emulsifiers, which are used to create its smooth texture, prevent ice crystals and mix the fats and water within it,’ he said. 

The most common synthetic emulsifiers found in store-bought ice creams include mono- and diglycerides — also referred to as E471 — as well as carrageenan and polysorbate 80 — or E433.

Around 10 per cent of the British population are also estimated to have some level of dairy intolerance to ice cream.

For this group, the sugars found in milk — called lactose — ferment in the colon, causing bloating, gas and diarrhoea. 

For a more gut healthy alternative, try fermented yoghurt, like kefir, or greek yoghurt variants, says Mr Haworth. 

Research shows that these products introduce live, beneficial bacteria that supplement the existing gut microbiome, promoting a better balance and preventing harmful bacteria from flourishing. 

Fermentation also predigests some nutrients, making them easier to absorb, and strengthen the gut lining. 

‘Interestingly, data on dairy consumption shows that people who consume more fermented dairy typically have lower levels of inflammation than those who eat less,’ he said. 

‘While your stomach may react to some forms of dairy — like ice cream — other types could actually help build healthy gut bacteria.’

Low-sugar sodas and sweets 

Whilst too much sugar feeds harmful gut bacteria and promotes inflammation, damaging the gut lining, sweeteners aren’t much better, warn experts. 

Animal studies have shown that sweeteners can shift the balance of gut microbes, reducing beneficial bacteria and increasing potentially harmful ones, leading to an unhealthy gut environment. 

They’ve also been shown to directly weaken the intestinal lining, damaging the gut barrier and increasing susceptibility to inflammation and infection. 

‘If you’re overweight or want to maintain your weight, you’re probably going to be eating more sweeteners,’ says GI physiologist Jordan Haworth. 

‘This can negatively impact the gut microbiome and as well as metabolism, however.’ 

A human research study published in 2023 mapped the effect of different sweeteners on the body. 

Scientists found that two of the most popular — sucralose (sold as Splenda) and saccharine — changed both the gut microbiome and how the body processed blood sugar. 

Another, aspartame, wasn’t found to disrupt the gut microbiome. It has since, however, been classified as possibly carcinogenic to humans — though research is mixed.

One Diet Coke a day is fine, says Mr Haworth — but if you’re prone to drinking more than that, you may want to swap to a more gut-healthy fermented drink like kombucha.  

Adrienne Benjamin, gut health nutritionist at ProVen Biotics, also warns that lower-sugar chocolates, gummies and baked goods marketed as ‘mindful’ often rely on sugar alcohols and alternative sweeteners. 

‘Ingredients like erythritol, sorbitol and chicory root fibre may reduce sugar content, but they’re notorious for impacting digestion,’ she explained.

‘Ironically, these ‘healthier’ sweets can lead to more gut discomfort than traditional versions.’ 

Vegan cheese

Vegan cheeses may remain a staple for plant-based eaters, but their ingredient lists can be surprisingly bad for the gut, says nutritionist Adrienne Benjamin.

‘Many faux cheeses are made with refined oils, starches and stabilisers that offer little nutritional value and can irritate the gut lining,’ she explained. 

Vegan cheeses also tend to lack the live cultures found in fermented dairy that can be beneficial for gut health. 

To avoid this, look for dairy-free cheeses that are primarily comprised of whole foods like ground nuts and seeds or cooked vegetables with added spices to mimic cheese flavors, say experts. 

These less processed versions are likely to have more fibre and healthy fat, and fewer ultra-processed ingredients. 

Oysters 

The single worst food for gut health is anything that might make you sick, says physiologist Jordan Haworth. 

And at the top of that list are oysters. 

‘Food poisoning and tummy bugs are the single biggest cause of long term gut issues like irritable bowel syndrome (IBS),’ he explained. 

Bacterial toxins that cause food poisoning damage the gut by triggering inflammation and nerve overstimulation — which causes the trademark intense cramping and diarrhoea. 

The immune system launches a strong attack in response, but this hypervigilance can sometimes lead it to attack healthy gut cells and nerves, compounding the damage.

‘If you already have a diet high in fibre, you’re more likely to recover, whereas if you have a poor diet, you’ll have less bacteria that can fend off those bugs,’ said Mr Haworth. 

But sometimes, the only thing that can prevent food poisoning is avoiding the culprit itself. 

‘I always avoid oysters,’ explained Mr Haworth. ‘They pick up a lot of viruses in the water, and as there’s been a rise in UK sewage spills in the last couple of years, there’s also been a rise in oyster-carried viruses.’ 

‘Nowadays, I won’t eat them unless they’re fully cooked. People say oysters are an aphrodisiac, but I say there’s nothing sexy about the squits.’ 

Fried foods 

Foods cooked in oil — especially if deep fried — can also damage the gut, says Mr Haworth. 

‘When you fry oils at high temperatures they become oxidised — meaning they break down,’ he explained. 

‘These oxidised compounds have been linked to negative changes in the gut microbiome, so I try to limit fried food whenever possible.’

The fats and oils used to cook fried foods — commonly things like vegetable, soy and canola oil — are also harder for our body to digest, which can cause digestive woes like gas, stomach pain and diarhhoea. 

If you are frying something, stick to extra virgin olive oil, says Mr Haworth, as this is the healthiest oil to cook with. 

‘The polyphenols [natural compounds found in plants] in EVOO actually protect the food from oxidising,’ he explained, ‘making it a much better option for cooking.’