The fermented foods raising your heart attack risk (and what to eat instead)

 From kefir to kimchi, “gut-friendly” foods have become a staple of the modern diet. But could our enthusiasm for fermented foods be quietly undermining heart health?

The answer, according to the British Heart Foundation (BHF), is yes (in some cases). While many gut-friendly foods support the microbiome, “some come with a ‘health halo’ that distracts from what’s inside – often high levels of salt, sugar or calories that can raise blood pressure and affect weight or blood sugar control,” explains Tracy Parker, the charity’s nutrition lead.

Meanwhile, “a diet high in sugar and fat, and low in fibre, can encourage gut bacteria to produce compounds which increase inflammation and contribute to atherosclerosis – the fatty build-up in arteries that raises the risk of heart attack and stroke,” she adds.

With that in mind, the BHF is urging people to be more mindful of their intake of gut-friendly foods “by checking labels, watching salt and sugar, and keeping portions sensible so any benefits aren’t lost,” Parker says.

That said, a healthy gut remains important for the heart. “When we eat a diet rich in fibre, and whole, unprocessed foods, our gut bacteria produce helpful substances that can reduce inflammation and may lower blood pressure,” Parker says.

Of course, not all gut health products pose risks for the heart. But identifying the healthiest options in the supermarket is not always straightforward. So, we asked Parker and Nichola Ludlam-Raine, specialist registered dietitian and author of the book How Not to Eat Ultra-Processed, to explain which fermented foods are best for your health, and the red flags to avoid.

Kimchi

A traditional Korean dish, made from salted, fermented cabbage and seasoned with chilli powder, garlic, ginger and fish sauce, kimchi has surged in global popularity in recent years. During fermentation, the naturally occurring “good” bacteria in the cabbage multiply, meaning some varieties are considered probiotic, Parker explains. Probiotics are “live” bacteria or yeast with health benefits – often labelled “good” or “friendly”.

Research suggests that regular, moderate consumption of kimchi supports a healthy gut, and could play a role in immunity, improving the body’s ability to respond to infections and weight loss.

Red flags

However, kimchi is typically high in salt. “Many commercial versions contain around 1.6g of salt per 100g,” Parker says. With UK guidance set at no more than 6g of salt per day, some shop-bought varieties are classified as red on traffic-light labels.

Whilst the recommended serving of kimchi is around 80g, “large or frequent portions can easily push someone over the [daily salt limit], which can raise blood pressure and increase heart disease risk,” Parker adds. A large BMJ meta-analysis found that higher salt intake is associated with a 23 per cent increase in stroke risk and a 14 per cent increase in cardiovascular disease risk.

Plus, kimchi products which are not labelled “raw”, “unpasteurised” or as containing “live cultures” will not provide probiotic benefits, while still delivering the same salt content, Parker says.

Top tips

During your food shop, look for lower-salt versions of kimchi, and those labelled “raw” or “unpasteurised”, Ludlam-Raine says. “Lower salt” labels aren’t always consistent, so look for products with less than 1.5g of salt per 100g. Fresh, refrigerated varieties are more likely to contain live cultures than shelf-stable versions.

Stick to around a tablespoon (roughly 15g) and use kimchi as a condiment rather than a main component, Ludlam-Raine says. Pair it with fibre-rich foods such as wholegrains, vegetables or salads.

If you are making kimchi at home, “use a variety of vegetables (not just cabbage) to boost fibre and microbial diversity, and stick to around 2 to 3 per cent salt by weight to support safe fermentation without excess sodium,” Ludlam-Raine adds. She recommends adding garlic, ginger and chilli to increase beneficial plant compounds.

Kombucha

Once a niche health drink, kombucha is now widely available in supermarkets and high-street cafés. “It is considered a probiotic because it is made by fermenting sweetened tea with a live culture [known as a SCOBY, or a symbiotic culture of bacteria and yeast]” Parker explains. “The bacteria feed on the sugar and multiply, creating a slightly fizzy drink full of helpful microbes”.

One 2022 review found that kombucha may improve digestion and boost metabolism. It provides antioxidants in the form of polyphenols, and these may help to reduce inflammation and prevent cell damage.

Red flags

Yet, while marketed as a healthier alternative to fizzy drinks, “many shop-bought kombuchas still contain significant amounts of free sugars,” Parker says. A standard fizzy drink contains around 33g of sugar per 330ml can – the UK’s recommended daily limit. Some kombuchas contain around 12g per serving as it is the primary food source for the SCOBY, so essential fuel for the fermentation process – however, this is “almost half an adult’s recommended daily limit for free sugar, consumed in one sitting,” Parker says.

One study published in Nutrients found that drinking two or more servings of sugary drinks per day was associated with a 50 per cent higher risk of dying from heart disease or stroke compared to those who drank less. Plus, a wealth of research links added sugars to high blood pressure, inflammation, weight gain and diabetes.

Top tips

“Treat sweetened kombucha like a soft drink and have it only occasionally, and consider diluting it with sparkling water,” Parker says. “Avoid drinking it with cakes, biscuits or sweets, as this will double up the sugar load.”

Always check the label and opt for a low-sugar kombucha, or one with no added sugar, Ludlam-Raine adds.

If you are making kombucha at home, “use good-quality black or green tea for polyphenols, and ferment for around seven to 10 days to reduce sugar without it becoming overly acidic,” Ludlam-Raine says. Flavour it with fruits or herbs rather than adding more sugar, she advises.