Probiotics are among the most popular supplements people take, along with vitamins and minerals. But choosing the right probiotic — or knowing whether you should even take one — can be a daunting task. Walk down any supermarket aisle and you’ll find dozens of options. How do you know which one is right for you? We’ll help you demystify probiotics so you can answer that question with confidence. The most significant conclusion from our research: probiotics do little to benefit people who are generally healthy; rather, they demonstrate benefits for those of us with certain medical disorders. So, what are probiotics and are they right for you?

Beyond bacteria: what are probiotics?

The official definition of probiotics are “live microorganisms which when administered in adequate amounts confers a health benefit on the host.” This is a pretty broad definition, so let’s break it down:

• Live microorganisms: Most people think of bacteria like Lactobacillus or Bifidobacterium — the bacteria used in yogurt — when they think of probiotics. But there are several other bacteria and even yeasts that can be used as probiotics. Importantly, the microorganisms must be alive to be effective.
• Adequate amounts: If there aren’t enough bacteria or yeast in the probiotic, no effects will be seen. The “adequate amount” depends on which microorganism(s) comprise the probiotic, what the probiotic is being used for, and the bacteria already present in a person (i.e., the specific, unique characteristics of an individual’s microbiome).
• Health benefit: Contrary to popular opinion, there is little to no evidence that probiotics can be used to maintain health in already healthy individuals. However, several probiotics can be used to treat several diseases, which are outlined in the following section.

What are the health benefits of probiotics?

You might be surprised to know that probiotics aren’t just for the gut. Probiotics can be applied to the skin to treat skin allergies and eczema or in the mouth to support oral health. Even probiotics that are destined for the intestines can affect other parts of the body, such as the respiratory tract. 

So, how do they work? They can affect the body in a few different ways:

• Probiotics can help restore a microbiome harmed by substances such as antibiotics or by infections.
• Probiotics produce substances that can have beneficial effects, such as vitamins or short-chain fatty acids (SCFAs).
• Probiotics can influence the immune response.

The symptoms of a number of different diseases can be ameliorated with probiotics. Importantly, each disease requires a different combination of microorganisms because probiotics are as diverse as the conditions they are designed to treat. Some diseases that can be treated with antibiotics have been summarized by the National Institutes for Health (NIH) and include:

• Diarrhea resulting from antibiotic treatment or chemotherapy
• Clostridioides difficile infection
• Constipation
• Inflammatory bowel disease and irritable bowel syndrome
• Infant colic
• Necrotizing enterocolitis
• Infant sepsis
• Hay fever
• Asthma
• Atopic dermatitis
• Acne
• Upper respiratory tract infections (including COVID-19)
• Urinary tract infections

Are probiotics safe?

Most probiotics consist of microorganisms considered by the FDA as GRAS: generally recognized as safe for consumption. Typically, the worst side effect a person might experience from a probiotic is indigestion/intestinal discomfort. However, some people, such as those with compromised immune systems, might be at risk for more serious side effects, including:

• Infections
• Production of harmful (instead of beneficial) substances
• Transfer of antibiotic resistance genes to a person’s microbiome

If you suffer from any of the conditions listed in the previous section and think a probiotic could help you, your doctor can help you figure out which probiotic to take.

Grocery store probiotic foods

You can find a variety of probiotics, from digestive “shots” to fifty brands of yogurt, at the grocery store. Many of these are delicious and contain other beneficial ingredients, such as antioxidant ginger or anti-inflammatory turmeric. However, they may contain so much sugar that any potential beneficial effects are likely negated. 

All of them do have one thing in common: in contrast to probiotics specifically developed to address disease, all of these are marketed for one thing — supporting intestinal health and well-being. The jury is still out on whether this is true or not. So, when buying a probiotic at the grocery store, keep a few things in mind:

• Avoid probiotics with added sugars.
• Select probiotics from brands with a good reputation. If you’re not sure, you can check a third-party certifier like ConsumerLab or ask your doctor.
• You might have to try a few different probiotics to figure out which one works best for you.
• If you want a probiotic to address a specific issue, such as IBS or diarrhea, it’s best to ask your doctor to prescribe a well-tested probiotic than to find one at the grocery store. Grocery store probiotics have not been scientifically tested for their ability to treat disease.
• If you’re already healthy, you’re probably better served by simply eating a diet rich in prebiotic foods, rather than taking a probiotic.

Are fermented foods probiotics?

Fermented foods can be thought of as “natural” probiotics because they aren’t grown in laboratories and then formulated into pills or powders or added to foods later. Fermented foods are whole foods that are in the process of being digested by bacteria and yeast. Kombucha, kimchi, and kefir are just a couple of examples of fermented foods.

Eating a food instead of taking a pill or powder might seem like the healthier choice, but the truth is that whether and how fermented foods might be beneficial is even more mysterious than probiotics. Most evidence around the benefits of fermented foods, in contrast to probiotics, is anecdotal. However, some studies do suggest that fermented foods are a great source of nutrition because they have already been pre-digested by bacteria and yeast, freeing up nutrients for faster absorption in the human gut. And, generally, fermented foods are rich in prebiotic fiber, which provides its own set of benefits.

Key takeaways

Probiotics — live microorganisms that confer a health benefit when administered — are an optional intervention for people with specific diseases, such as IBD, diarrhea, and constipation. While many probiotic species have been designed and well-studied for their ability to treat disease, the probiotics you can get at your local grocery store are not among the most rigorously scientifically tested probiotics. They might be delicious to eat, but if you’re already healthy, you can do a better job of maintaining a healthy gut by eating a diet full of fiber-rich whole foods. 

Check out our article on probiotics vs prebiotics for more information.