How to Select a Probiotic

Probiotics are beneficial strains of bacteria and yeasts that can be taken as supplements to support the gut microbiome.

They help to maintain the balance of gut flora by crowding out pathogens that could cause illness. Probiotics produce beneficial compounds such as short-chain fatty acids, which nourish the cells lining the colon and help maintain the integrity of the intestinal barrier.

Probiotics play a significant role in supporting immune system function, as around 70% of the immune system is located in the gut. They also help alleviate symptoms of irritable bowel syndrome, and help to prevent or reduce diarrhea (particularly antibiotic-associated diarrhea).

Certain probiotic strains may help lower cholesterol levels, support heart health, and even influence mental health through the gut-brain axis, and help maintain vaginal health in women.

Probiotics are categorized by their genus, species, and strain. The most common (and most studied) genera are Lactobacillus, Bifidobacterium, and Saccharomyces. You might also find supplements that contain Streptococcus, Enterococcus, Escherichia, and Bacillus.

Both lactobacilli and bifidobacteria are non-spore-forming, gram-positive, lactic acid-producing bacteria, but they have some key differences.

• Lactobacilli
  Lactobacillus bacteria are primarily found in the small intestine, mouth, and vagina, and are naturally present in many fermented foods such as yogurt, kefir, and sauerkraut. Lactobacillus species are known for producing lactic acid, which helps create an acidic environment that inhibits the growth of harmful bacteria and supports healthy pH levels in various parts of the body.¹
  Lactobacillus strains are often associated with digestive health, immune support, and maintaining vaginal health in women. Some strains are shown to treat or prevent urinary tract infections and yeast overgrowth. Lactobacillus are also effective in preventing antibiotic-associated diarrhea and supporting lactose digestion.²

• Bifidobacteria
  Bifidobacterium mostly colonizes the large intestine (colon). They are among the first to colonize the gut in newborns and remain abundant throughout life, though their numbers tend to decline with age. Bifidobacterium species are less present in fermented foods and are more often consumed in probiotic supplements. They ferment complex carbohydrates and fiber in the colon, producing beneficial short-chain fatty acids such as butyrate, acetate, and propionate, which serve as fuel for colon cells and have anti-inflammatory properties.³

• Saccharomyces
  Saccharomyces is a genus of beneficial yeast. Saccharomyces boulardii is the main probiotic species, known for its ability to survive stomach acid and antibiotics. It is highly effective in preventing and treating various types of diarrhea, including antibiotic-associated diarrhea, traveler's diarrhea, and C. difficile infections.⁴
  S. boulardii produces enzymes that help break down toxins from harmful bacteria and support the intestinal barrier function. It also has anti-inflammatory properties and can support normal gut flora during and after antibiotics or illness. It is heat-stable and doesn't require refrigeration.⁵

The number of colony-forming units (CFU) indicates the number of viable cells in the product - i.e., the total number of live bacteria that can properly colonize the gut and provide their health benefits.

The efficacy of probiotic bacteria depends on whether they survive both storage and the harsh environment of the gut.  Many factors such as pH, acidity, oxygen exposure, flavoring agents, packaging materials, and storage conditions can affect their ability to colonize the gut.

An optimal CFU should be between 10-50 billion, as the recommended minimum effective CFU dose per day is 10⁸–10⁹ cells.⁶ Some products may contain up to 50 billion CFU or more. Look for a ‘guaranteed CFU’: this will mean that the probiotic bacteria are alive until the end of the shelf life, not just at the date of manufacture.

One exception is spore-based probiotics, as they remain dormant until they are consumed. They also withstand the passage through the gastrointestinal tract and only become active upon reaching the large intestine, where they can begin colonizing the gut.

Different strains vary by their benefits and evidence.

The label on a probiotic supplement should list the exact strains (e.g., Lactobacillus acidophilus LA-14 or Bifidobacterium longum BB536) rather than just the genus name. Do some research on what strains may be best suited to the specific health condition you want to treat.

Also consider whether you want a single-strain or multi-strain formula, as both have their advantages depending on your health goals. Research suggests that a multi-strain formula provides the greatest benefits to your wellbeing.⁷

Probiotics that have been third-party tested have undergone rigorous testing by an independent laboratory. This ensures that they contain both the number of bacteria and the specified strains stated on the label.

Third-party testing also certifies that the product meets industry standards, is safe for consumption, and free from contaminants such as pesticides, heavy metals, and unwanted bacteria.

Supplement manufacturers can maximize the efficacy of their probiotic products through techniques such as micro-encapsulation or combining different synergistic strains, prebiotics, and/or nutrients.

It’s advisable to avoid cheap probiotics. These are likely to have low-quality ingredients, low or inaccurate CFU counts, and an ineffective delivery system.

Also avoid products that don’t specify strains or quantities or that have not been stored correctly.