Probiotics are live microorganisms that are available as dietary supplements, medications, or in certain foods and are intended to help support the intestinal flora. But how do probiotics work, what should you pay attention to when taking them, and which applications have been scientifically studied? In this article, you’ll learn everything you need to know about probiotics, their potential benefits, and when taking them might be beneficial.
Probiotics at a glance
- Probiotics contain live bacterial cultures such as lactic acid bacteria, bifidobacteria, or yeasts, which are intended to support the intestinal flora. Their effects are still being further researched.
- It is important to take probiotics as gastric acid-resistant capsules or as spore-forming bacteria, as these are better protected from stomach acid.
- Take probiotics during meals or 30 minutes before – this increases the survival rate of the bacteria.
- A minimum daily dose of 10 billion CFU (colony-forming units) is recommended.
- Different bacterial strains have different effects. Researchers are investigating their effects on weight, diarrhea after antibiotics, chronic intestinal diseases, and mental health, among other things.
- Probiotic foods include yogurt, kefir, sauerkraut, kimchi, apple cider vinegar, and sourdough bread.
- People with weakened immune systems, chronic illnesses, short bowel syndrome, or pregnant women should consult a doctor before taking probiotics.
What are probiotics?
Probiotics are foods, medications, or dietary supplements that contain specific live bacterial cultures. Probiotic bacteria are among the “good” intestinal bacteria; they are intended to support the intestines and the intestinal flora living there.
Probiotics usually contain lactic acid bacteria (lactobacilli) and bifidobacteria, sometimes also yeasts or spore-forming bacteria. Such microorganisms occur naturally in some foods that have been consumed for a long time, such as yogurt, kefir, sauerkraut, and sourdough bread. Nowadays, however, they are also added to specific foods or sold as capsules, powder, or tablets—these products are then called probiotics.
How exactly and how sustainably probiotics change and influence the intestinal flora is currently being researched.
What should I look for when taking probiotics?
You can take probiotics in capsule, powder, or tablet form. It’s worth paying attention to a few things to get the most out of them.
The supplements must be able to bypass stomach acid. This can be achieved, for example, through enteric-coated capsules. Most modern probiotics meet this criterion, but it’s still worth checking when purchasing. Some dietary supplements also contain spore-forming bacteria, which are naturally resistant to the acidic environment of the stomach thanks to their protective spore coating.
Take probiotics with or 30 minutes before eating. Studies show this increases the likelihood of more bacteria surviving the journey to the gut [1].
The bacteria should be present in sufficient quantities in the preparation. Billions of microorganisms live in the intestine. For probiotics to have an effect, they must be dosed sufficiently high. The dose is expressed in colony-forming units (CFU) per gram. Experts recommend that probiotic preparations contain a daily dose of at least 1, preferably 10 billion CFU – commercially available probiotics typically contain between 10 and 50 billion CFU. Higher doses within this range may be useful if you want to address specific problems, such as diarrhea after antibiotic therapy [2].
Probiotics are not a substitute for other therapies. If you want to treat diseases and conditions, it’s best to consider probiotics as a complement to other measures such as medication and dietary changes.
Do not confuse probiotics and prebiotics. Prebiotics are certain fibers that our intestines cannot digest. Instead, they serve as food for intestinal bacteria and can, for example, promote the proliferation of health-promoting bifidobacteria. Prebiotics are processed into dietary supplements; in nature, they occur in berries, legumes, onions, and garlic, among other foods.
Do different strains of bacteria work differently?
It’s worth paying attention to the exact strains of bacteria in the product. You can always find this information in the ingredients list. Not all of them have been studied equally well in scientific studies, and certain bacteria also appear to have different effects on health and well-being. For example, it’s been well researched how certain lactobacilli and bifidobacteria can influence diarrhea as a side effect of antibiotics.
Here are some examples of the areas in which certain strains of intestinal bacteria have been researched:
- Obesity and cardiovascular health: Some strains – such as Lactobacillus plantarum, Lactobacillus acidophilus, Lactobacillus gasseri, Enterococcus faecium, Streptococcus thermophilus – have been linked in studies to lower BMI, waist circumference, and blood pressure.
- Diarrhea caused by antibiotic use: Probiotics have been shown in studies to help treat diarrhea caused by antibiotics. Strains that have shown efficacy in studies include Lactobacillus adophilus, Lactobacillus casei, Bifidobacterium longum, and Bifidobacterium subtilis. Bacillus clausii is often used in children.
- Alleviating symptoms of intestinal diseases: There have been studies in which, for example, Lactobacillus reuteri alleviated the symptoms of irritable bowel syndrome, or the use of Escherichia coli was investigated in inflammatory bowel diseases.
- Depression and anxiety: Lactobacilli and bifidobacteria also have an effect on mood and mental health in some studies. In one study, Lactobacillus helveticus and Bifidobacterium longum reduced aggressive thoughts and ruminations that occurred during a sad mood.
When are probiotics useful?
Probiotics are recommended in various situations – for example, during or after antibiotic therapy or when psychological problems occur simultaneously with digestive problems.
If you experience symptoms like bloating, constipation, and stomach rumbling, this could also be a sign of an imbalance in your gut flora. In this case, you can try probiotics. Just keep in mind that it may take some time to see results, and that you may experience side effects like bloating at first, especially if you’re new to probiotics [3].
Here we present some applications of probiotics that are currently being researched in more detail by scientists.
Research on probiotics and intestinal diseases
According to a 2024 study summary, probiotics may reduce the risk of gastrointestinal disorders, boost the immune system, and improve metabolic health [6]. There is scientific evidence that probiotics may alleviate the symptoms of irritable bowel syndrome. [7]
Probiotics are also being investigated in connection with chronic inflammatory bowel diseases such as Crohn’s disease and ulcerative colitis. Studies here are also promising. Probiotic supplements have shown faster resolution of Crohn’s disease flare-ups and reduced the number of new flare-ups. This may be because a greater diversity of intestinal bacteria helps inhibit inflammation [8]Â .
Probiotics and mental health
The gut and brain constantly communicate with each other and influence each other. The connection between the two is so close that it is often referred to today as a gut-brain axis. This also means that the composition of the gut flora influences mood and mental health. For example, symptoms such as flatulence often occur in depression [9].
Scientists have been investigating for several years whether probiotics can also help with mental illnesses. In many studies, probiotics have been able to slightly reduce the symptoms of depression and anxiety disorders; doctors now often recommend probiotic supplements in combination with measures such as psychotherapy and medication. Importantly, in some studies, it took four to nine weeks for such effects to become apparent.
It’s best to talk to your therapists and doctors if you have mental health issues and want to try probiotics – this can be especially useful if you also suffer from digestive problems.
Probiotics in antibiotic therapy
Antibiotics are used to fight infections caused by pathogenic bacteria. This can also lead to the loss of some of the “good” intestinal flora. If this leads to the proliferation of harmful bacteria, the microbiome becomes unbalanced, a condition known as dysbiosis.
There are now studies that show that antibiotic therapy can reduce the diversity of the intestinal flora – scientists are investigating this by testing how many bacterial species can be detected in stool samples and using this to calculate the diversity index for the microbiome.
It is therefore often recommended to take probiotics during antibiotic therapy. However, studies have not proven that this simultaneous intake protects the intestinal flora from a loss of diversity. This was shown by study summaries published in the renowned journals BMC Medicine and Nature in 2023 and 2024.
After taking antibiotics, you will probably need to work over a longer period of time to rebuild your intestinal flora, for example, with prebiotics, probiotics, and a high-fiber diet.
However, it may still be worthwhile to take probiotics in addition to the antibiotic. Studies have shown that certain probiotics can alleviate other side effects of antibiotic therapy. They particularly reduced the risk of diarrhea, but also, for example, gastrointestinal infections during treatment.
Which foods contain probiotics?
Lactic acid bacteria and other probiotic microbes are formed during fermentation, for example, during the fermentation or ripening of foods. Therefore, only very specific foods are probiotic, for example:
- Fermented dairy products such as yogurt and kefir
- Mature, unpasteurized hard cheese, for example, Cheddar, Gruyère, Gouda, Parmesan
- Fresh sauerkraut, kimchi
- Pickled cucumbers or pickles (most pickled cucumbers from the supermarket are not probiotic)
- Apple cider vinegar
- Sourdough bread
Who should not take probiotics?
When you take probiotics, you are always introducing microorganisms that don’t yet live in your body. Probiotics are generally considered safe. However, a risk cannot be ruled out for certain groups of people because there is still little research data on specific groups and diseases. If you belong to one of the following groups, you should discuss taking probiotics with your doctor beforehand [16] :
- Pregnant and breastfeeding women
- People who have a weakened immune system due to an illness or who take immunosuppressive medications, for example, for certain autoimmune diseases.
- People with certain chronic diseases, such as pancreatitis
- People with short bowel syndrome
If you are currently suffering from acute gastrointestinal infections, for example, due to an infection with norovirus or rotavirus, you should also not take probiotics until you are healthy again.
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