Probiotics: The science of what they are and how they work

With the growing interest in gut health, you’re likely to come across many different products with probiotics on the label. But even if you see the word “probiotic” on a product label, what’s inside may not be the real thing. In addition, probiotics are often misunderstood, and many people have questions about what they are and whether they might be helpful.

Here’s the summary of what scientists know about probiotics and how they work.

What are probiotics?

Probiotics are live microorganisms that improve your health when taken in the right amounts.

Not every live microorganism in a food product or supplement is a probiotic. To qualify as a probiotic, the amount and types of the live microorganisms must be known, and they must be scientifically tested to provide a benefit. Safe, live microbes that haven’t been tested this way are not called probiotics – instead they’re called live cultures.

Probiotics can be found in a variety of food products, such as yogurt or infant formula, or in dietary supplements. Generally the live microorganisms found in fermented foods such as kimchi and miso are not considered probiotics because they’re a wild mixture of microorganisms at an unknown dose.

One clue that a live microorganism is a true probiotic is that it has one or more strain names listed on the label. Strain names come in three parts: the genus, the species, and the strain designation. For example: Bifidobacterium infantis Ab42.

Are probiotics only for gut health?

Even though the increased focus on gut health has made probiotics more popular than ever, probiotics aren’t just for the gut. Certain probiotics have been developed to be applied to other parts of the body (for example, probiotic cream for the skin), and qualify as probiotics as long as they result in a measurable health benefit.

What’s the difference between probiotics and prebiotics?

Probiotics are beneficial live microbes that you ingest or apply directly, whereas prebiotics are non-living substances that serve as food (or “substrates”) that help beneficial live microbes (which may be already in or on your body) to thrive.

The various microorganisms living in your gut prefer different kinds of food, so any prebiotic you consume will feed only certain members of the community of microorganisms, providing you with specific health benefits — depending on the qualities of the prebiotic and which microorganisms it is feeding.

Both probiotics and prebiotics can be effective ways to manage certain health conditions, and they can also work together.

How probiotics are used

Probiotics are best when you use them for a specific purpose, which matches with the research conducted on them. Legitimate probiotic products intended for humans have been studied in real people and shown to provide a health benefit of some kind. If a product hasn’t been studied, it doesn’t qualify as a true probiotic. Here’s a summary of the health benefits that probiotics are shown to give you.

What are probiotics good for?

Different probiotics are effective for supporting your health in different ways. Specific probiotics have been shown to do the following in generally healthy adults and/or children:

• Help your immune system function properly and reduce levels of inflammation
• Reduce digestive symptoms and aid your digestive function
• Reduce antibiotic-associated diarrhea
• Improve lactose intolerance
• Decrease some common infections, including those of the respiratory tract, gut, and vaginal tract

No single probiotic will deliver all of these benefits at once, so you need to choose a probiotic that’s backed by science to give you the benefit you’re looking for.

Most of the benefits of probiotics that scientists have discovered so far are related to gastrointestinal health or the immune system. But probiotic research is a hot area of science and many possible applications for probiotics may be found in the years ahead.

What probiotic foods are good to add to your diet?

If you’re looking for specific probiotic benefits, commercial yogurt or fermented food products with strains listed on the labels may be a good choice for adding to your diet. Selected strains have often been tested to bring you benefits to immune or gastrointestinal health.

However, in general, consumption of foods with live cultures, even if they haven’t been studied for specific probiotic benefits, are also associated with benefits for general health and wellness. Some foods contain a high number of these live cultures: kimchi, sauerkraut, miso, and cultured dairy products such as sour cream and yoghurt.

Will probiotics work for me?

Like all ways to promote health, many factors unique to you may influence what works for you and what doesn’t.  The same is true for probiotics. Any specific probiotic strain might not work for everyone. Scientists think the factors that might influence whether a probiotic works for you could include your unique diet, the existing microbes in your digestive tract, what medications you may be taking, and your personal physiology.

One strategy for figuring out whether a probiotic works for you is to try a product for about a month. If you don’t see the benefit you’re looking for, then perhaps it’s not the right one for you. Prebiotics and fermented foods with live microorganisms are alternative ways that you can address your health through the gut.

The science behind probiotic supplements

It’s time to drill down further into the science. What do scientists know about probiotics, and the best way to use them?

Does it matter which probiotic I use?

The probiotic you use should depend on why you’re taking it, since different strains have different effects as demonstrated in scientific studies. One guide that helps you choose a probiotic with evidence for a certain health benefit is “A Clinical Guide for Probiotic Products Available in the USA”. (You can also check out this short video.)

If you don’t have a specific health need in mind, and simply want to promote wellness through consuming more live microbes, you can choose any probiotic from a reputable brand.

Do probiotics require a prescription?

Depending on where you live, probiotics are generally not classified as medicines and do not require a prescription.

But remember, if you have a serious medical condition – especially one involving the gastrointestinal tract or deficient immune system – then you should talk to your doctor before consuming probiotics.

Do probiotics have to be taken every day?

Scientists don’t know for sure that probiotics need to be taken daily, but in the vast majority of the studies the dose that results in a health benefit is given daily. Since probiotics typically do not stick around in the gut for long after they have been consumed, regular doses are probably necessary for ongoing benefits.

How do probiotics help the immune system?

Probiotics can help the immune system by interacting with immune cells within the digestive tract, where much of the body’s immune system resides. The effects of these interactions can tune the function of the entire immune system, improving how we respond to threats such as harmful microorganisms or allergens, or affecting levels of inflammation throughout the body.

In line with these actions, certain probiotic strains have been shown to reduce the incidence, severity, and/or duration of infections such as the common cold, gastroenteritis, or urinary tract infections.  

Do probiotics affect the brain?

Throughout history, humans have evolved with microbes living all around us. Even some primitive creatures are shown to have certain aspects of their brains influenced by gut microbes.

The gut and the brain are connected via a two-way communication channel called the gut-brain axis, which scientists have known about for a long time. But the many ways in which microbes influence the brain through the gut-brain axis is an active area of research today. Some human studies show certain probiotics can have benefits for brain function or mood in some people. But research is still early, and many researchers have been disappointed that promising studies in animal models have not translated into successes in humans yet.

Some probiotic strains produce (or encourage your existing gut microbes to produce) neurochemicals, including oxytocin, gamma-aminobutyric acid, serotonin, tryptamine, noradrenaline, dopamine, or acetylcholine. Scientists continue to investigate what this could mean for both healthy people and those with brain-related disorders.

How many probiotics per day should I take?

If you’re taking probiotics to help with a specific health condition, it is best to take the particular dose which was used in the research, to give you the best chance of receiving a similar benefit. You might find a recommended dose provided by the manufacturer on the label, or you can consult with a health care practitioner to receive the right advice for your situation.

For maintaining wellness, scientists haven’t yet established a dose of probiotics that is guaranteed to benefit general health. However, a large-scale study of dietary patterns in the United States found that consuming a higher dose of live cultures per day was associated with a range of health benefits such as better blood pressure and blood sugar regulation, and a lower weight.

What happens to probiotics in the stomach?

The stomach is an acidic place where many microbes have difficulty surviving. What happens to live microorganisms in the stomach really depends on the type of microbes and what they are equipped to do.

Some microorganisms cannot survive in this acidic environment but others thrive. Traditionally, potential probiotic species were tested for acid resistance during research and development stages, as the ability of probiotics to survive the entire journey through the stomach and intestines was believed to be needed for their effectiveness. 

Do probiotics need to be alive through the digestive tract?

Survival of the microorganisms in the stomach may not be critical for the probiotics’ effectiveness.

Although there is little doubt that the ability of probiotics to grow and metabolize as they travel through the digestive tract can contribute to health benefits, emerging evidence suggests that dead microbes may be able to have some beneficial effects, too.

Probiotic safety

It’s not only important to know whether probiotics are effective for a given health benefit. It’s also important to know if probiotics are safe. Typically probiotics have a good safety record from the hundreds of studies completed to date, but here’s what you need to know about safety precautions.

Are probiotics safe?

Probiotics are safe for most people, as shown by a very low rate of unwanted side effects in the studies on probiotics. However, you should talk with a medical professional before taking probiotics if you suffer from an immune disorder or short bowel syndrome, or if you have a serious illness. You should also check with a medical professional before giving probiotics to an infant, especially a premature infant.

Can probiotics cause abdominal pain?

Probiotics should not lead to extreme abdominal discomfort or pain. If they do, stop taking them. Probiotics can impact how your gut feels, however, and sometimes cause a change in digestive symptoms for a period of time until your gut environment adapts to them.

Are probiotics safe for babies?

Not all probiotics are recommended for babies. Certain probiotics have been tested in young children and shown to be effective for a health condition (such as reducing crying time in a colicky baby) and are safe for this population. Be sure to use probiotic products or foods specifically designed for infants and consult with a healthcare practitioner to seek advice tailored for your baby.

Is it safe to drink alcohol while taking a probiotic supplement?

Probiotics and alcohol are not known to cause any harmful effects from their interactions. However, alcohol may affect your gut environment and possibly interfere with the beneficial effects of the probiotics. Any alcohol is best consumed in moderation.

Are probiotics safe during pregnancy?

Most studies have found that probiotics are safe in pregnancy and certain formulations can bring health benefits to either the mother or the fetus. For example, probiotic supplementation has been generally shown across studies to reduce the incidence and severity of gestational diabetes mellitus in pregnant women. However, the evidence for some other conditions is mixed. While some studies have found probiotics effective for preeclampsia prevention, one analysis found probiotic supplementation during pregnancy was associated with an increased risk of preeclampsia in some women with preexisting obesity. Talk with a healthcare professional when starting to take probiotics during pregnancy.

How probiotics work

How probiotics work within the body to achieve health benefits is a hot topic of scientific study. Scientists don’t currently know how every probiotic works, but they do know some of the mechanisms by which probiotics have their effects.

How do probiotics work?

Scientists still have a lot to discover about how probiotics work, and different probiotics work in different ways. Here are some of the mechanisms that probiotics use behind the scenes to give you a health benefit:

• Interacting with your immune system
• Crowding out harmful microbes
• Producing beneficial substance, such as vitamins, short chain fatty acids, and digestive enzymes (including those that help you digest milk)
• Influencing the activities of your existing gut microbes

Do probiotics help the gut microbiome?

Materials on gut health often assert that probiotics help your gut microbiome by adding beneficial microorganisms, but scientifically this isn’t completely true. Rarely do probiotics find a place in the gut microbiome and stick around for the long term. However, they can promote a gut environment that is more favorable for beneficial microbes, or work in many other different ways, so they often still give you a health benefit even if they don’t take up residence permanently in the gut.

Consumer choices about probiotics

What does all of this information mean for the probiotic choices that you and your family make? Here are some answers to common questions about choosing probiotics for use at home.

How do you store probiotics?

Probiotics should be stored according to the instructions on the label. Some need to be refrigerated, and others do not. The qualities of different probiotic strains as well as the manufacturing processes for the product influence the storage conditions required for the specified shelf life. The live microorganisms in a product gradually die off over time, so make sure you consume them before the best-before date on the package if you want to receive an effective dose.

Are probiotics regulated?

A common myth is that probiotics are not regulated, but this is false. Every country has regulations applicable to probiotics, with the regulations depending on the probiotics’ intended use.

Countries differ on the exact regulations as well as the enforcement of those regulations in the marketplace.

What are the best probiotic products?

The best probiotic products are those that have scientific evidence supporting the particular benefits you are looking for, with the right dose of microbes, produced under quality manufacturing conditions, with clear labeling of the probiotic strain, storage conditions, and the number of viable microbes through to the end of the shelf life. Many probiotics have no evidence for giving you any health benefit, so if you want good value from your purchase it’s better to choose one that’s science-backed. Ask a healthcare professional to help you know which ones have scientific evidence showing they’re effective.