Gut-friendly foods such as kimchi and kombucha may carry hidden risks for heart health when eaten in excess, the British Heart Foundation (BHF) has warned.

The charity said foods marketed as prebiotic, probiotic or otherwise good for the gut can support the microbiome, but some may also be high in salt or sugar, which can raise the risk of cardiovascular disease.

Products highlighted by the British Heart Foundation included kimchi, kombucha, fruit yoghurts, smoothies and sauerkraut. It said there is no harm in including them as part of a healthy diet, but advised people to check labels for added salt and sugar and eat them in moderation.

Tracy Parker, the charity’s nutrition lead, said: “We encourage everyone to choose foods that can keep their gut microbiome healthy. The benefits are clear, and we are continuing to improve our understanding of how a gut-friendly diet may help our hearts.

“A lot of these products can contain high levels of salt or sugar though, so it is important to be aware of the potential drawbacks.

“By ensuring you check package labels for added salt and sugars, and eat each in moderation, you can make sure the risks do not outweigh the benefits for your heart health.”

Fermented foods such as kimchi and sauerkraut are rich in probiotics, the healthy bacteria produced during fermentation that can help support a diverse and healthy gut microbiome.

However, both are traditionally made using a lot of salt, which can raise blood pressure if eaten frequently or in large quantities. High blood pressure is known to increase the risk of heart attack and stroke.

Kombucha, a fermented tea, also contains probiotics and can be a healthier alternative to fizzy drinks, but many commercial and shop-bought versions contain added sugar.

Eating too much sugar can lead to weight gain, which can increase the risk of heart attack, stroke and other cardiovascular disease.

Fruit yoghurts can contain probiotic live bacteria cultures, but may also be high in sugar and have fewer live cultures than plain versions.

The charity said plain yoghurt with live and active cultures on the label can be a lower-sugar option, with whole fruit added at home for sweetness.

Smoothies made with whole fruits provide prebiotic fibre, which feeds beneficial gut bacteria and supports digestive health.

They can also provide vitamins and antioxidants, especially when made with a variety of plant-based ingredients.

But blending breaks down the structure of fruit, releasing free sugars that behave like added sugars in the body and can cause faster rises in blood sugar levels.

Regularly consuming too much sugar can lead to weight gain, which can increase the risk of developing type 2 diabetes, heart disease and kidney disease.

The charity said only one 150ml serving of any smoothie counts towards five-a-day, and suggested adding nuts or seeds for extra protein and fibre to help keep blood sugar levels more stable.

The BHF also noted that some shop-bought sauerkraut is pasteurised, which removes most of the live bacteria.

It advised checking the label, eating small portions and choosing unpasteurised products for those seeking the probiotic benefits.

The charity said beneficial gut bacteria produce short-chain fatty acids during digestion, which are linked to reduced inflammation, better metabolism and better heart and circulatory health.

These good bacteria also help digest polyphenols, natural plant chemicals thought to have antioxidant properties and which may help lower blood pressure.

By contrast, harmful gut bacteria, which thrive on diets high in fat and red meat, produce chemicals that can cause problems in the heart and blood vessels by increasing inflammation and altering how cholesterol is processed in the body.

Beneficial bacteria thrive on varied diets high in prebiotics, non-digestible fibres found in foods such as wholegrains, oats, beans, lentils, bananas and onions.