Probiotics and prebiotics – is it safe to use them to treat disease?

July 18, 2018 by Amreen Bashir, The Conversation
Bifidobacterium bacteria. Credit: Kateryna Kon/

The link between gut microbes and health is now well established. As a result, researchers have been investigating the effects of probiotics, prebiotics and synbiotics on various diseases. Worryingly, though, they haven't been reporting on the safety of these treatments – as one would for a drug trial.

A new review of 384 randomised controlled , published in Annals of Internal Medicine, found that information on the safety of these supplements is either lacking or not reported.

More than a quarter of the trials (28%) didn't report any harms data, and safety results weren't reported in 37% of the studies. Of the studies that did mention harms, 37% used only "generic statements" to describe , and 16% used "inadequate metrics", according to the researchers.

So what?

But what's all the fuss about, you might wonder? Aren't these all natural products that are available in supermarkets and health food shops? Indeed, the two main families of , Lactobacillus and Bifidobacterium, are found in many fermented foods, such as sauerkraut, kimchi and yogurt.

Prebiotics don't even contain bacteria, they are merely food on which probiotics feast. They are fibres that can't be absorbed or broken down by the body, but they nourish friendly bacteria, particularly the Bifidobacteria genus. Bananas, onions, garlic and legumes are natural sources.

Synbiotics are foods or supplements that combine probiotics and prebiotics.

Probiotic bacteria are found in fermented foods. Credit: marekuliasz/

Although these products all sound harmless, and may not do any harm to a healthy person, a good clinical trial should always report adverse events (harms). Trials involving these supplements are often in patients who are severely ill or physically vulnerable, such as preterm babies, so the effect of probiotics, prebiotics or synbiotics might be different in these patients.

Several case studies have reported an increased risk of fungaemia – the presence of fungi or yeasts in the blood – in people treated with probiotics. This complication is rare and it tends to happen in people with suppressed immune systems, but it is serious.

Probiotics can have serious adverse effects in other vulnerable groups. For example, a 24-year-old woman, who was administered probiotics before surgery, developed sepsis.

In the past few years, use in hospitals has increased greatly. However, there is growing evidence that the use of probiotics in patients with organ failure, compromised immune systems and those whose intestinal barrier mechanisms are impaired increases the risk of infection.

A trial in the Netherlands, designed to see whether probiotics could reduce the incidence of infectious complications in patients with severe acute pancreatitis, ended up being investigated after 15 died unexpectedly.

A few trials involving probiotics have reported on adverse events in vulnerable groups, such as the elderly, and found no serious harms. But these trials tend to have very low participant numbers, reducing the significance of the claims.

It is clear that there is an urgent need for standard safety and administration protocols for probiotics in clinical trials.

An earlier version of this article stated that the 15 people with pancreatitis who died while taking part in a trial in The Netherlands were given Yakult. This is incorrect. The trial participants were administered a multispecies probiotic preparation, administered enterally (via a tube, directly to the gut). Yakult played no part in the study and none of their products were used in the study. The Conversation UK apologises for this error.

Explore further: Jury still out on probiotics

Related Stories

Jury still out on probiotics

July 17, 2018
(HealthDay)—Probiotics have become a trendy dietary supplement, with more and more people popping bacteria-laden capsules to try to improve their gut health.

Should healthy people take probiotic supplements?

June 18, 2018
A visit to the supermarket these days can feel more like walking through a pharmacy, with an ever-expanding range of milks, yoghurts, pills, powders and speciality foods promoting their "probiotic" prowess.

Probiotics prevent diarrhoea related to antibiotic use

May 30, 2013
Probiotic supplements have the potential to prevent diarrhoea caused by antibiotics, according to a new Cochrane systematic review. The authors studied Clostridium difficile (C. difficile) infections in patients taking antibiotics ...

Probiotic supplements failed to prevent babies' infections

July 3, 2017
(HealthDay)—Probiotic supplements may not protect babies from catching colds or stomach bugs in day care, a new clinical trial suggests.

Research reveals zero proof probiotics can ease your anxiety

June 20, 2018
If you're expecting probiotics to reduce your anxiety, it might be time to put down that yogurt spoon—or supplement bottle—and call a professional instead.

Consuming probiotics promotes weight loss and reduces BMI

July 11, 2016
Consuming probiotics, so-called 'good bacteria', can reduce body weight and body mass index (BMI) according to a new meta-analysis published in the International Journal of Food Sciences and Nutrition.

Recommended for you

Your heart hates air pollution. Portable filters could help

November 13, 2018
Microscopic particles floating in the air we breathe come from sources such as fossil fuel combustion, fires, cigarettes and vehicles. Known as fine particulate matter, this form of air pollution increases the risk of cardiovascular ...

Simple tips can lead to better food choices

November 13, 2018
A few easily learned tips on eating and food choice can increase amount of healthy food choices between 5 percent and 11 percent, a new Yale University study has found.

No accounting for these tastes: Artificial flavors a mystery

November 13, 2018
Six artificial flavors are being ordered out of the food supply in a dispute over their safety, but good luck to anyone who wants to know which cookies, candies or drinks they're in.

Insufficient sleep in children is associated with poor diet, obesity and more screen time

November 13, 2018
A new study conducted among more than 177,000 students suggests that insufficient sleep duration is associated with an unhealthy lifestyle profile among children and adolescents.

New exercise guidelines: Move more, sit less, start younger

November 12, 2018
Move more, sit less and get kids active as young as age 3, say new federal guidelines that stress that any amount and any type of exercise helps health.

Some activity fine for kids recovering from concussions, docs say

November 12, 2018
(HealthDay)—Children and teens who suffer a sports-related concussion should reduce, but not eliminate, physical and mental activity in the days after their injury, an American Academy of Pediatrics report says.


Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.