The sour truth about kefir: Experts reveal how trendy ‘off-milk’ drink can destroy your gut health

Fermented milk may not seem like everyone’s beverage of choice.

But the number of people in the UK consuming the healthy drink, also known as kefir, is growing rapidly.

According to experts, the number of patients reporting side effects of kefir is the same.

Kefir has been consumed for thousands of years and first appeared in Russia and Mongolia.

But in recent years, it has become increasingly popular due to its much-hyped health benefits. Tesco has reported a 400 per cent increase in kefir sales in 2024 compared to just 18 months ago.

The drink contains billions of good bacteria, called friendly microbes, that promote gut health. Research shows that having these bacteria in the gut above average has far-reaching positive effects.

These include reducing the risk of heart disease, obesity, infections and even bowel cancer.

‘I drink kefir every day,’ says Jordan Haworth, a digestive health specialist at the Microbiome Clinic in London, which offers gut microbiome testing.

‘It’s probably a superfood. ‘It contains about 10 to 20 times more good bacteria than yoghurt, as well as protein, calcium and other vitamins.’

However, experts say kefir is not risk-free. Some people may experience uncomfortable side effects when consuming the milk drink. For others, kefir may aggravate existing medical problems.

In rare cases, kefir can even trigger a serious infection.

So what are the dangers of kefir? So how can you avoid them?

Read on to learn more…

Be careful about drinking kefir too early

Experts say that the sudden increase in bacteria in the intestine caused by kefir can lead to painful symptoms.

Kefir, made by combining aged milk with bacteria- and yeast-filled grains, typically contains about two billion microbes per serving.

The tangy taste of kefir may not appeal to everyone’s taste, but the fermented milk drink has a growing fan base and is flying off the shelves.

Mr Haworth says this improves gut health in the long term, but can have negative effects in the short term.

Research shows that people who start drinking kefir for the first time often experience gas, bloating, cramps, diarrhea or loose stools.

This is because new bacteria begin to ferment carbohydrates, such as bread or pasta, in the intestine. This produces excess gas.

Experts say that the best way to prevent this problem is to start by consuming kefir in small portions and gradually increase the dose over time.

‘With kefir, it’s best to start low and go slowly,’ says Mr Haworth. ‘Most people should be able to manage a small glass a day. A large glass could cause problems.’

Kefir may make stomach problems worse – not better

It’s often touted as a cure for intestinal problems, but experts say kefir can make some digestive problems worse.

One of these is irritable bowel syndrome, also known as IBS; It is a painful condition that affects around one in ten Britons. It often causes abdominal pain and diarrhea.

Because it is still unclear what triggers IBS, there is no licensed treatment. But growing evidence suggests that bacteria-filled drinks like kefir, collectively known as probiotics, may help combat symptoms.

This is because research suggests that IBS patients tend to have low levels of good gut bacteria.

But for some, experts say kefir can have the opposite effect. This is because the increase in gas levels that trigger higher levels of carbohydrate fermentation can further aggravate the already irritated intestinal surface.

Similarly, drinking kefir may also worsen the symptoms of patients with a condition called small intestinal bacterial overgrowth, or SIBO.

This occurs when excess bacteria in the small intestine (part of the intestines) causes gas to build up and triggers bloating, pain, and diarrhea.

Consuming kefir can increase this painful gas formation, says Mr Haworth. ‘Kefir can cause bloating in people with IBS and SIBO,’ he adds. ‘You don’t necessarily need to avoid it, just limit your consumption.’

The ‘good’ bacteria in kefir may be dangerous for some

In extreme cases, probiotics such as kefir can trigger dangerous infections.

This is because in patients with severely weakened immune systems, new bacteria from the drink can harm the body.

Last year, Japanese doctors explained how one of their patients died after taking a kefir-like probiotic.

In a medical review published in the British Medical Journal, medics detailed how the 70-year-old man was initially hospitalized with Covid and an unrelated bacterial infection.

While he was recovering in hospital, he was advised to start taking probiotics to deal with the ongoing intestinal problems he was experiencing.

But two months later he was admitted to hospital complaining of ‘severe, persistent’ pain in his abdomen due to internal swelling caused by the infection.

When doctors tested his blood, they found that the infection was caused by a bacteria called Clostridium butyricum; This bacteria was also present in the probiotic supplement he took.

The man developed sepsis, in which his immune system overreacts to an infection, leading to organ failure and death.

Doctors linked the weakened immune system to the Covid infection and his long-standing alcohol problem. They concluded that this allowed the bacteria found in the probiotic to infect and spread throughout the body.

Therefore, experts say that patients with serious health problems such as HIV or who have recently been treated for cancer should talk to their doctors before starting to drink kefir.