Perhaps you've heard about probiotics, but you're not quite sure what they are or how they work. After all, their use is becoming more common, with approximately 4 million American adults reporting recent use. In fact, probiotics or prebiotics are the third most commonly used dietary supplement in the U.S. But what's the difference between probiotics and prebiotics? And how do you know which you need? What information do you need so you know how to choose a probiotic that's right for you?
Let's explore the world of probiotics and prebiotics—and how they work to improve your gut health. In this article, we'll dive into what are probiotics, the role of the gut-brain axis, the most commonly asked questions about probiotics, and how to choose a probiotic that works for you!
Let’s talk about flora. So, throughout your body you have lots of “tenants,” if you will. These are bacteria, or flora, that live on your skin and inside your body, particularly within your digestive system. They make up what’s called your microbiome.
When these bacteria, or microorganisms, are in balance, all is usually well. But, when these bacteria are out of balance, you begin to see all sorts of health problems appear—and not necessarily just gut health issues. That’s because the balance between the different kinds, or species, of these organisms is critical.
There are certain kinds of flora or microorganisms that are “good” and others that are “bad” or that can become problematic if they get out of hand—meaning there are too many of them in your system. Or, on the flipside, your body doesn’t have enough of the “good” bacteria.
This is where probiotics come in. Probiotics are also live microorganisms—they are the “good” kind. They are administered in supplement form. But supplements are not the only sources of probiotics. You can also get them from some foods, particularly fermented foods. Why is that? Because fermented foods rely on good bacteria, the same kind your body needs.
So, how do probiotics work? By eating foods that contain probiotics you help to increase the number of flora in your gastrointestinal system that are needed to help break down food and absorb nutrients. Foods that contain probiotics include things like yogurt (but not the typical sugar-laden kind; check the labels for probiotic content), sauerkraut, miso, and kefir.
Probiotic supplements do the same thing, but they come in a more concentrated dose, often containing specific strains to produce a specific health benefit. Each capsule contains (or should contain—more on that later) billions of healthy live bacteria that will help your body better digest your food.
The health benefits of probiotics are extensive. A healthy balance of flora in your microbiome is key to all areas of your health, including your skin, cardiovascular system and your nervous system. [1, 2, 3, 4]
Like many things in life, a healthy digestive system, and your overall health, is about balance. Yet many of us lead lives that are hectic and stressful and definitely out of balance. In the next section, I explain how stress and digestion are also tied to probiotics.
Our gut and our brain are communicating all the time. This connection actually has a name, the “brain-gut axis,” or BGA. Believe it or not, the bacteria in your gut are a key part of this communication system. They play a role in the development and maintenance of neurotransmitters and hormones as well as wellbeing of your immune system. 
So, maybe it’s no surprise that illnesses that affect your gut are often stress-related. These include conditions such as irritable bowel syndrome (IBS) and GERD. But other conditions are also affected by your gut health, including eczema and sinusitis. Basically, the interplay between stress, your gut microbiome, central nervous system, and your immune system is a delicate balance. If you’re in a chronic state of stress, over time this can lead to a weakened immune system and a host of other health problems. 
I get a lot of questions from my patients about probiotics, so I wanted to share some of the ones I hear most often with you. Hopefully, this will help you to have a better understanding of how probiotics work, plus some of the issues they can and can’t help.
In the next section, I also share my recommendations on how to choose a probiotic. Ultimately, I want to give you knowledge that will empower you on your health journey.
In general, the difference between prebiotics and probiotics supplements is that prebiotics “feed” probiotics. Prebiotic foods are those that contain plenty of fiber, such as vegetables and fruits. Examples of prebiotic foods include asparagus, bananas, garlic, onion, and seaweed. The probiotic bacteria in your digestive system then break down and ferment this fiber, which helps encourage proper digestion and absorption of nutrients.
A healthy relationship between prebiotics in your diet and appropriate amounts of probiotic strains in your system again helps to ensure not only a healthy digestive system, but also overall health, including a strong immune system, nervous system, cardiovascular system and skin health. 
One easy way to get plenty of prebiotic foods in your diet is to eat a plant-based diet. You can also try prebiotic supplements.
I should note, however, that if you have a significantly imbalanced flora, or SIBO, sometimes adding too many prebiotics (whether in food or supplement form), can cause excessive symptoms. In these cases, I usually recommend focusing on the probiotics first.
Yes and no. Research has shown that in many cases, probiotics can actually help prevent and treat diarrhea.  That said, sometimes when you start taking a new probiotic, you may experience diarrhea or other side effects. However, if it continues, it may also mean that this probiotic is not a good fit for you.
We each have an individualized microbiome and what one person needs may not be the same as what someone else needs. It’s important to purchase a reputable probiotic and to check the product label on the probiotic to see what strains are included and other key details. Keep reading because I explain how to choose a probiotic in more depth in the next section.
Probiotics are generally safe, especially if you purchase high-quality products from a reputable source. That said, there have been some reported cases of gastrointestinal infections and inflammation related to probiotic use. And probiotics can sometimes cause side effects such as bloating, gas, and flatulence. 
See my section below on how to choose a probiotic to help guide you in selecting an effective probiotic. However, you should also speak with your doctor first, especially if you have a gastrointestinal or metabolic disorder or other medical condition.
Similar to other gastrointestinal symptoms, this can go either way. If your body is adjusting to a probiotic or the probiotic doesn’t “agree” with you, it may cause bloating. However, research has also shown that probiotics can help with bloating in some cases.
For example, a study on the influence of probiotics on IBS patients published in the American Journal of Gastroenterology found that the participants who received the probiotic strain Lactobacillus plantarum experienced less flatulence and pain than those in the control group. 
Here’s the thing about probiotics and weight loss. Simply taking a probiotic supplement won’t cause dramatic weight loss. However, your flora is important in maintaining a healthy weight.
Studies have shown that having an overgrowth of unhealthy flora in your system can make it difficult for you to lose weight. Basically, certain strains of bacteria prevent weight loss.
If you eat a lot of processed foods and don’t get enough fiber in your diet from vegetables, fruits, nuts, and seeds, your body doesn’t get the nutrients it needs to be healthy and balanced. Plus, processed foods contain a lot of preservatives, which also impact the body’s flora. And if your body is stressed due to gastrointestinal problems, it will hold on to more weight.
So, yes, probiotics can help you lose weight in the sense that they are part of your bigger health picture. They are part of your overall health. Probiotics will help balance your microbiome, but you also have to first eat healthy foods, move your body, and practice self-care that helps you manage stress. 
Now that you have a better understanding of what probiotics are and how they can help, here are some of my recommendations on how to choose a probiotic that’s right for you. Remember, you always want to talk to your doctor or healthcare provider first before starting a new supplement, especially if you have any medical conditions.
The first thing to remember is that probiotics are live microorganisms, so one of the most important things to look at is the time of manufacture, or the expiration date on the bottle. You also want to be sure the product you purchase contains several probiotic strains. The strains most-recommended are lactobacillus and bifidobacterium strains, particularly Lactobacillus rhamnosus and Bifidobacterium bifidum. Another recommended strain known as Saccharomyces boulardii is actually a probiotic yeast. [14, 15]
A reputable probiotic company should be able to tell you the source of the probiotic, the viability, the safety, and stability of their product. If they do not have this information, be leery of the product’s viability.
Unfortunately, many of the probiotics you find on the shelf at your pharmacy are not as viable as you may think. And not all strains are equal. As a general rule, I like probiotics that are multi-strain, verified shelf stable, with a minimum of 20 billion CFUs (verified post-manufacturing), and without prebiotics unless your physician determines otherwise.
In order for a microorganism to be considered an effective probiotic, there are a number of hurdles that must occur in the manufacturing process.
In addition to isolating the appropriate strain of microorganism, it has to be effectively delivered through the acidic stomach to the intestines and be in enough quantity to produce an effect.
Some important information to consider when considering how to choose a probiotic includes the source of the microorganism (animal, soil, fermented foods, human gut); the number of CFUs and whether that number is pre- or post-manufacturing; the expiration date; and the form of the probiotic (live, freeze-dried, vacuum-dried), which will affect its viability.
Questions to consider when determining how to choose a probiotic: