Among the latest fermented foods popular with the health-conscious is kombucha. Picture: Supplied

Fermented foods, from sourdough to kombucha, may be terribly trendy right now but it appears they can cause some deeply unfashionable side-effects.

These include bloating, headaches and allergies, a microbiologist has warned.

Fermentation has been used for thousands of years to preserve foods from yoghurt to sauerkraut.

However, it has become especially fashionable in recent years because of supposed "probiotic" benefits to our digestion.

Among the latest fermented foods popular with the health-conscious is kombucha, which is a mix of yeast and bacteria fermented with black or green tea, and kefir, a fermented milk drink. 

Such products, which also include yoghurt, sauerkraut and a popular Korean dish of fermented vegetables called kimchi, can boost the trillions of beneficial bacteria that live in the human gut.

However, microbiologist Dr Manal Mohammed, of the University of Westminster, has warned that certain fermented products may cause problems for some of us.

They produce compounds called amines, which Dr Mohammed says can stimulate the central nervous system and alter blood flow, triggering headaches and migraines. 

Fermented foods also contain histamines which a small number of people cannot digest properly and develop symptoms including hives, vomiting, sleep problems and an irregular heartbeat.

Dr Mohammed wrote on The Conversation website: "While there are a wide variety of health benefits that can happen from consuming fermented foods, these may not work for everyone."

The most common reaction to fermented foods, according to Dr Mohammed, is bloating, which can often be painful. That is because, when probiotics such as those found in yoghurt, kill harmful gut bacteria, gas is produced.

Her online article states that probiotics are safe for the majority of people, but can cause infection for those with a compromised immune system. They can even carry genes which might make us resistant to important antibiotics used to treat sexually transmitted infections and respiratory problems.

Dr Mohammed said: "Fermented foods have become very popular, thanks to claims about their nutritional properties and reported health benefits. Though they might offer many health perks, most people aren’t aware that they might not work for everyone."

Daily Mail