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The purpose of probiotics

To understand probiotics, it helps to start with a crash course on the microbiome.

¡°You can think about the gut microbiome as a bustling city with trillions of residents,¡± says Ajami, executive director of MD Anderson¡¯s Platform for Innovative Microbiome and Translational Research (PRIME-TR).

Much like a real city, your gut microbiome is always active. While factors like your genetics shape your microbiome, so do lifestyle choices, ranging from diet to where you live. Instead of people, the residents of your gut microbiome are microorganisms like bacteria, fungi and viruses. Most of these microorganisms are harmless and help your body function. Among these bacteria are probiotics, Ajami explains.

¡°You can consider probiotics as the good residents,¡± he says.

Probiotics help support your microbiome, which plays a central role in your overall health. A balanced microbiome influences not only digestion, but also the function of the immune system, organs and tissues throughout the body. Because of these wide-ranging effects, changes in the microbiome have been linked to chronic diseases, including cancer. At PRIME-TR, researchers are studying how the microbiome influences cancer risk and how it affects an individual¡¯s response to cancer treatments, including immunotherapy.

Types of probiotic supplements

While probiotics in the gut are shaped by diet and lifestyle, many people turn to supplements as an alternative way to influence their microbiome. With so many options available, the world of probiotic supplements can seem almost as densely populated as the microbiome itself.

¡°Probiotic supplements are really different depending on if you're just grabbing an over-the-counter one off the shelf at the drug store for no reason versus if your doctor recommends that you take a certain probiotic for a certain condition,¡± says Daniel-MacDougall, a nutritional epidemiologist who studies diet and the microbiome.

Within the category of probiotic supplements, you'll find over-the-counter supplements and live biotherapeutics. Here¡¯s a closer look at the differences between these groups:

Over-the-counter probiotic supplements:

• Are dietary supplements
• Are available without a prescription
• Aren¡¯t reviewed for safety and effectiveness by the 

Live biotherapeutics:

• Are designed for medical use
• Require a prescription
• Treat specific medical conditions
• Go through the same FDA regulations as other medications

It¡¯s better to get probiotics from food, not supplements ¡ª here's why

Both experts recommend that healthy individuals get probiotics from foods rather than over-the-counter supplements.

Examples of probiotic foods include:

• Yogurt
• Kefir
• Sauerkraut
• Fermented fruits and vegetables

¡°We do not recommend that patients or really anyone go and find solutions at the supplement aisle of stores,¡± Ajami says. ¡°You can get what you need through whole foods.¡±

Here are some reasons why.

It's hard to know exactly what you¡¯re getting in a supplement

Supplement quality and ingredients can vary greatly from product to product.

¡°What you find in the aisles of stores are products that are, for the most part, not regulated. And that means it's very hard to tell if what's on the label is actually what's in the bottle,¡± Ajami says. ¡°It's very hard to tell that the claims made in those labels are actually supported by science and rigorous clinical trials.¡±

Daniel-MacDougall shares Ajami¡¯s concern about over-the-counter probiotic supplements. These supplements may have limitations, including whether they contain live bacteria, the variety of probiotics they contain and their ability to reach the gut where they can be used, she notes.

Taking unnecessary probiotic supplements can do more harm than good

Everyone¡¯s microbiome is different and exists in a delicate balance. A probiotic supplement that helps one person might not help you.

¡°Just like you wouldn¡¯t take a medication that you don't need or that is not designed for your issue, probiotics can work the same way,¡± Daniel-MacDougall says.

On the flip side, probiotic supplements could disrupt or displace some of the good bacteria you already have, she notes. This could lead to an upset stomach, digestive problems or feeling bloated.

¡°Taking some mix of bacteria without knowing what you need or what effect it's going to have can be risky. You may have no effect, you may have GI side effects, or it could potentially have a benefit. You just don't know,¡± she says.

Probiotic foods provide additional nutrients

When you eat probiotic foods, you aren¡¯t only getting probiotics. You¡¯re also getting a variety of other nutrients.

So, while an over-the-counter probiotic supplement may contain some probiotics, yogurt offers probiotics plus fatty acids and amino acids (proteins). All of these nutrients work together to stimulate your microbiome, MacDougall explains.

¡°Dietary supplements are almost never an effective replacement for food,¡± she says.

What cancer patients should know about probiotic supplements

Our experts don't recommend taking over-the-counter probiotics during cancer treatment.

While over-the-counter probiotic supplements may seem like an easy way to help your body respond to cancer treatment, they can have the opposite effect. This is because the probiotics in over-the-counter supplements may compete with the bacteria that already live in your body, Ajami says.

For example, in a , melanoma patients on immune checkpoint inhibitors who ate low-fiber diets and took over-the-counter probiotic supplements had worse outcomes than patients who ate enough fiber and didn¡¯t take over-the-counter probiotic supplements.

It¡¯s well known that microbiome composition can impact how your body responds to cancer treatment. However, Ajami notes the microbiome modulation used at MD Anderson is very different than taking an over-the-counter probiotic supplement.

¡°This is not DIY. It is under clinical supervision, under trials, under the supervision and the oversight of clinical teams,¡± he says.

When to talk to your doctor about probiotic supplements

Challenges to your gut microbiome ¡ª think after antibiotics, bowel prep or foodborne illness ¡ª can cause gastrointestinal issues and may lead you to feel that you need a probiotic supplement, Daniel-MacDougall says.

In these cases, talk to your doctor for personalized advice on how to proceed.

¡°Physicians who give certain antibiotics may have a better understanding of how this works for their patients,¡± she says. ¡°It's not as precise and personalized yet as we'd all like it to be, but there is some level of clinical knowledge.¡±

Additionally, in some cases, probiotics from food or supplements may help individuals with irritable bowel syndrome, Crohn's disease or other health problems. But they also could potentially cause harm if used improperly or in combination with other medications.

Ultimately, trying to solve unknown gut problems with a probiotic supplement could feed the bad bacteria in your gut and make the problem worse. That's why it's important to address underlying issues before adding supplements, Daniel-MacDougall says.

Support your gut microbiome with these healthy habits

You might see ads that say probiotics can help with constipation, irregular stool and bloating. In these cases, should you look to probiotic supplements for a possible fix?

¡°If I see a person with bloating and poor stool habits, I don't immediately assume I need to fix their microbiome. I think they need to fix the habits that are causing their microbiome to go out of whack,¡± Daniel-MacDougall says.

Instead of looking in the drugstore for a solution, try these tips.

Move your body

Aim for 150 minutes of moderate physical activity or 75 minutes of vigorous exercise each week to help lower your cancer risk.

Eat healthy foods

Eat a healthy diet and drink enough water.

Along with probiotic foods, other foods that promote gut health include fiber-filled options. Fiber is a prebiotic that the helpful bacteria in your gut can digest and use, Ajami explains.

So, focus on eating a variety of healthy foods, such as whole grains, vegetables, fruits, beans, nuts and seeds. The more colorful, the better.

Variety in your gut microbiome helps your gut respond to different conditions. It¡¯s a lot like a garden. If you only grow roses, a problem like a pest or a freeze could ruin your entire garden. But if you have many different types of plants, it¡¯s more likely some of your garden will survive. The same goes for your gut microbiome, he explains.

¡°If you're eating a lot of different types of foods, very colorful plates, usually you will have a colorful gut in terms of bacterial composition, and that is generally a good thing,¡± he says.

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