|March 7, 2024

What are Probiotics?

By Bulletproof Staff
Reviewed by Theresa Greenwell for Scientific Accuracy on 11/01/2023

What are Probiotics?

  • Probiotics are the good gut bacteria normally found in your intestines. They support healthy digestion, support immunity, and synthesize certain vitamins, among other essential functions.
  • Modern life can negatively impact the balance of beneficial-to-harmful gut microbes. This can be due to overuse of antibiotics, poor diet, everyday stress, sleep issues and more.
  • Probiotic supplements support gut health by boosting the population of helpful bacteria. Not all strains or products yield the same benefits (from oral health and healthy weight to bloating and occasional constipation).
  • The most common and researched probiotic varieties belong to the Lactobacillus and Bifidobacterium genera.

The human body is estimated to contain as many bacteria as cells[1]. Probiotics are the beneficial microorganisms found in your body and especially your gut. They help keep their potentially harmful counterparts in check. Probiotics can also positively impact digestive health, immune function and more.

Probiotic supplements support gut health by increasing the population of beneficial bacteria, but not all strains or products yield the same results. The same goes for foods like yogurt and sauerkraut. Read on to learn how to choose the best probiotic foods and supplements, along with the science-backed benefits of probiotics. Additionally, we’ll talk about what are probiotics in greater detail.

What are probiotics?

Closeup of microbes

Probiotics are part of the microbiome,[2] the network of mostly bacteria that live on and in the human body. The microbiome[3] impacts how we interact with our environment. It also forms a network within the body, carrying molecules and chemical messages between the gut and brain. To be considered probiotics, microorganisms need to fulfill these criteria, according to the long-held definition from the World Health Organization:[4]

  • be live microorganisms. (This is important when shopping for supplements)
  • offer health benefits to the host (and cannot cause harm)
  • delivered in “adequate amounts”

Your gastrointestinal tract naturally contains its own unique colony of microbes.[5] However, modern life can negatively impact the balance of beneficial-to-harmful microbes. Antibiotic use, processed foods, everyday stress, poor sleep, and inactivity can all damage the microbiome.[6] Consuming probiotics can help recolonize the gut and bring back balance. A healthy microbiome:

  • digests food
  • synthesizes vitamins (including vitamin K and the B vitamins)[7]
  • rids the body of harmful microorganisms that can cause unbalance

What are probiotics going to do for your well-being? Supplementing with them can support gut health. Pair that habit with a nutrient-dense diet and other foundational health habits.

Related: Signs Your Gut Is Unhealthy and Why You Should Fix It

Science-Backed Benefits of Probiotics

Woman with hands over stomach

Digestion and Gut Health

Some strains show promise for occasional abdominal bloating, discomfort, flatulence as well as frequency and severity of bowel movements (plus quality of life) for those experiencing digestive discomfort. They have also proven helpful for occasional constipation.[8]


Ideally, your gut lining allows nutrients and helpful molecules to pass through to the bloodstream. Simultaneously, it keeps toxins and harmful microbes in the GI tract, excreting them as waste. Probiotics support your immunity by optimizing the gut wall’s permeability.

Healthy Weight

Research has shown a difference in the gut bacteria of lean individuals and those living with obesity.[9] While more research is needed, scientists believe weight and microbiome may be connected.[10] Some probiotics already appear to support a healthy weight.[11]

Oral Health

Digestion starts in the mouth, and so does the microbiome. A 2021 systemic review found that taking probiotics “influence favorably” the balance of bacteria in the mouth.[12] This offers benefits for bad breath, oral health and even dental health.

Choosing the Best Probiotic Strains and Probiotic Supplements

Probiotic capsules on table

When choosing a probiotic, look for certain strains, or types, of bacteria. They are usually measured in colony-forming units (CFU). This represents the number of live bacteria in each serving or dose.

Probiotics[13] are identified by their genus and species (collectively known as the strain). The most common and researched varieties belong to the Lactobacillus and Bifidobacterium genera.[14] Different species exert different effects. Moreover, not all species within those groups deliver the same benefits. Always read the labels of any supplement and first talk to your health-care provider.

The Bulletproof Express 3-in-1 Probiotic contains Bifidobacterium lactis, a shelf-stable probiotic strain that supports a healthy gut microbiome and GI tract. We use Bifidobacterium because it is one of the most clinically researched probiotic strains available.?This 3-in-1 supplement also contains prebiotic fiber to feed good bacteria and as well as Tributyrin, a postbiotic, to protect your gut lining, helping you feel relief from occasional GI discomfort.

Probiotic Foods

Naturally fermented foods and beverages like kimchi, sauerkraut, yogurt and kombucha contain living microbes. That is due to the lactic acid fermentation process used to make them. However, neither the amount nor the strain is enough to be classified as a probiotic in most cases, according to the nonprofit International Scientific Association for Probiotics and Prebiotics.[15]

To boost probiotic intake via foods, choose:

  • yogurt or kefir[16] with no added sugars. They should contain live or active cultures.
  • the best sources of prebiotic fiber.

Related: Move Over Probiotics. Synbiotics Are the Gut Supplement You Need

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