A Guide to Probiotics: All You Need to Know

Alex Kelly
Dec 4, 2025
6 min read

What are Probiotics?

Probiotics are live, beneficial microorganisms that support healthy digestion and overall gut balance. They help keep harmful bacteria in check, assist with breaking down food, and support immune function. You can get them through fermented foods like yogurt, kefir, sauerkraut, and kombucha, or through supplementation.

What About Prebiotics?

Prebiotics are types of fiber that your body cannot digest but your beneficial gut bacteria can. They are essentially food for probiotics, and help probiotics work better. Prebiotics are found naturally in foods like garlic, onions, bananas, asparagus, oats, and apples, or through supplementation.

Do You Need to Take Both Pre- and Probiotics?

Not necessarily. They can work well together, but it depends on your gut and your goals. The average person typically gets more prebiotics from their diet than probiotics, so many start with probiotics alone and only add prebiotics later if needed, and if they tolerate fiber well. *Prebiotics can cause gas and bloating in sensitive stomachs.

Kids usually do not need both as supplements. Most children get plenty of natural prebiotics from foods. Additionally, their gut bacteria is still developing, so adding a probiotic is often enough if they need support.

Understanding Groups, Species, and Strains

A probiotic GROUP is the big family it belongs to, like Lactobacillus. There are only a handful of major probiotic groups used in supplements and foods. The most common are Lactobacillus, Bifidobacterium, Saccharomyces, Bacillus, and Streptococcus. In total, there are around 10 to 15 groups that show up in human gut research.

Within a group you have different SPECIES, which are more specific types such as Lactobacillus rhamnosus or Lactobacillus acidophilus. There are dozens of species within a single group. Across all probiotic groups combines, there are well over 100 species that have been identified and studied.

The STRAIN is the most exact level and tells you the unique version of that probiotic and the precise benefit it's been studied for, like Lactobacillus rhamnosus GG. There are hundreds of species. Some estimate around 500 or more, and new strains continue to be discovered and studied. Supplements typically contain anywhere from one to about 20 strains, depending on the formula.

In short, the group is the broad category, the species is a specific member of that category, and the strain is the precise individual that has been studied for certain benefits.

Think of it like animals: Animal (group) → Dog (species) → Golden Retriever (strain)

Which Strain is Best for Me?

For the most targeted probiotic, the strain is the most important part to look at. The group and species tell you the general category of the bacteria, but the strain is the exact version that has been scientifically studied. Different strains within the same species can have different effects. For example, Lactobacillus rhamnosus GG helps with diarrhea, while another Lactobacillus strain may help more with immunity support. The species gives you a rough idea of what it might do, but the strain tells you the real, proven benefit.

"I'm an Overwhelmed Mom, There's over 500 Strains, Help!!!"

I get it. If you're overwhelmed, and do not have time to dig into every exact strain, it is completely fine to choose a probiotic based on the group or species that matches your goals. Strain specific probiotics are great when you want something very targeted, but most real world benefits still come from choosing the right group.

Your body does not require you to perfectly match every strain to get benefits. Many people feel noticeably better just by choosing the right group, especially if you are consistent. Strains are helpful when you want precision. Groups are perfectly fine when you want simplicity.

Top Probiotic Groups and Their Benefits

Lactobacillus group: supports digestion, reduces diarrhea, improves immunity, helps break down sugars, and supports vaginal health
Bifidobacterium group: supports colon health, improves stool regularity, reduces bloating, calms gut inflammation, and supports infant gut development
Streptococcus group: helps with lactose digestion and supports general gut balance (often found in yogurt)
Bacillus group: helps with gas, bloating, immune support, and stool consistency
Saccharomyces group: great for diarrhea, especially antibiotic related or travel related; helps rebalance the gut after disruption

Understanding CFUs

CFUs (colony forming units) are the way probiotics are measured. A CFU is simply a count of how many live and active microorganisms are in a probiotic dose. The number tells you how many bacteria are able to survive, multiply, and actually do their job in your gut.

Higher CFUs do not always mean a better product. For many people, doses between 1 billion and 10 billion CFUs are enough for daily support. Higher counts like 20 to 50 billion are usually used for targeted needs like acute diarrhea, after antibiotics, or specific gut issues. What matters most is choosing the right group or strain, then the CFU number that matches your needs.

Babies and kids generally need fewer CFUs than adults because their digestive systems are smaller and more sensitive. Babies usually do well with about 0.5 billion to 2 billion CFUs, while toddlers and young kids typically do best with 1 billion to 5 billion. Adults anywhere from 5-15 billion for general wellness, 10-20 billion for digestive support, 20-50 billion after antibiotic use.

Older kids can handle around 5 billion to 10 billion, especially if they are recovering from illness or taking antibiotics. More is not always better for children, so choosing the right probiotic group or strain matters more than choosing the highest CFU number.

There is no universal, globally accepted guideline with a dosing chart for probiotics by age. It really depends on the individualized need.

The good news is, regardless of CFU, a probiotic isn’t likely to cause harm. When asked if there’s such thing as “too much probiotic” Dr. Christine Waasdorp Hutado (MF, FAAP) says: "No. When you have prebiotics in your diet, the bacteria consume the amount they need to stay healthy and active. The rest passes through the digestive system into the stool. The same goes for probiotics. If you get too many, there's nowhere for them to go, so they also pass into the stool."

Most likely the “worse” that’s to happen if you are taking a probiotic that’s too strong is an upset stomach and loose stools. If this happens, consider lowering the CFU or switching to a probiotic with less strands.