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.

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.

Amounts Matter with Probiotics

Make sure your product contains the level of probiotics needed for the intended health benefit.

Check out this infographic, “Deciphering a probiotic label”, on how to read probiotic labels to find out how many live microorganisms (measured in colony-forming units) are present.

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Should Healthy People Take Probiotics?

This infographic, called “Probiotics for healthy people”, explains the scientific evidence for probiotic use in healthy individuals.

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What’s Important When Choosing a Probiotic?

There are many probiotic products on the shelves—read this handy “Probiotic checklist” for choosing one that meets your needs.

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Know the Real Science

Those who talk about probiotics don’t always get their facts straight—see our infographic called “Probiotics: dispelling myths”. Here’s a summary of how probiotics are different from the live cultures in fermented foods.

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Probiotics: the Cheat Sheet

See this infographic called “Probiotics” for an overview of exactly what probiotics are, where to find them, and what they can do for your health.

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ISAPP Videos

Check out these ISAPP educational videos to answer the most common questions about probiotics.

What is a probiotic?
Health benefits of probiotics
Are all probiotics the same?
How to choose a probiotic

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