Probiotics 101: A Simple Beginner’s Guide

By Kris Gunnars,
January 9, 2019 Updated: January 9, 2019

The bacteria in your body outnumber your body’s cells 10 to one. Most of these bacteria reside in your gut, and the majority are quite harmless.

Having the right gut bacteria is linked to numerous health benefits, including weight loss, improved digestion, enhanced immune function, healthier skin, better mood, and a reduced risk of many diseases (12).

Probiotics, which are a certain type of friendly bacteria, provide health benefits when eaten.

They are often taken as supplements that are supposed to colonize your gut with health-boosting microorganisms.

What Are Probiotics?

Probiotics are living microorganisms that, when ingested, provide numerous health benefits (3).



Probiotic foods include yogurt, kefir, sauerkraut, tempeh, and kimchi. Probiotics should not be confused with prebiotics, which are dietary fibers that help feed the friendly bacteria already in your gut (4).

Fermented preserved vegetarian food concept
Fermented preserved vegetarian food concept. Cabbage kimchi, sauerkraut sour glass jars over the rustic kitchen table. (Shutterstock)

Dozens of different probiotic bacteria offer health benefits.



Full fruit and greek yogurt breakfast bowl
Full fruit and greek yogurt breakfast bowl. Persimmon, apple, walnuts, pomegranates and natural yogurt. Healthy food concept on light background, top view. (Shutterstock)



Although the evidence is promising, more research is needed on the health benefits of probiotics (5).

Importance of Microorganisms for Your Gut


In fact, your gut contains hundreds of different types of microorganisms—as many as 1,000, according to some estimations.







However, not all organisms in your gut are friendly.

Your gut flora is highly sensitive to your diet, and studies show that an unbalanced gut flora is linked to numerous diseases (1516).

These diseases include obesity, type 2 diabetes, metabolic syndrome, heart disease, colorectal cancer, Alzheimer’s and depression (17181920).


Impact on Digestive Health

Probiotics are widely researched for their effects on digestive health (22).

Strong evidence suggests that probiotic supplements can help cure antibiotic-associated diarrhea (232425).

When people take antibiotics, especially for long periods of time, they often experience diarrhea—even long after the infection has been eradicated.

This is because the antibiotics kill many of the natural bacteria in your gut, which shifts gut balance and allows harmful bacteria to thrive.

Probiotics also combat irritable bowel syndrome, a common digestive disorder, reducing gas, bloating, constipation, diarrhea and other symptoms (262728).

Some studies also note benefits against inflammatory bowel diseases, such as Crohn’s disease and ulcerative colitis (29).

What’s more, probiotics may fight Helicobacter pylori infections, which are one of the main drivers of ulcers and stomach cancer (30313233).

If you currently have digestive problems that you can’t seem to vanquish, a probiotic supplement may be something to consider—though you should consider consulting with your doctor first.

Impact on Weight Loss

People who are obese have different gut bacteria than those who are lean (34).

Interestingly, animal studies indicate that fecal transplants from lean animals can make obese animals lose weight (3536).

Therefore, many scientists believe that your gut bacteria are important in determining body weight (3738).

Although more research is needed, some probiotic strains appear to aid weight loss (39).

In one study in 210 people with central obesity, which is characterized by excess belly fat, taking the probiotic Lactobacillus gasseri daily resulted in an 8.5% loss of belly fat over 12 weeks (40).

When participants stopped taking the probiotic, they gained the belly fat back within four weeks.

Evidence also suggests that Lactobacillus rhamnosus and Bifidobacterium lactis can assist with weight loss and obesity prevention—though this needs more research (41).

Conversely, some animal studies demonstrate that other probiotic strains could lead to weight gain, not loss (42).

Other Health Benefits

There are many other benefits of probiotics. They affect:

  • Blood cholesterol: Several probiotics have been shown to lower total and “bad” LDL cholesterol levels (4647).
  • Blood pressure: Probiotics may also cause modest reductions in blood pressure (4849).


Safety and Side Effects

Probiotics are generally well tolerated and considered safe for most people.

However, in the first few days, you may experience side effects related to digestion, such as gas and mild abdominal discomfort (53).

After you adjust, your digestion should begin improving.

In people with compromised immune systems, including those with HIV, AIDS and several other conditions, probiotics can lead to dangerous infections (54).

If you have a medical condition, consult with your doctor before taking a probiotic supplement.

The Bottom Line

Maintaining a healthy gut is about more than taking a probiotic supplement.

Day-to-day diet and exercise are just as important since many lifestyle factors impact your gut bacteria.


Kris Gunnars is a nutrition researcher with a bachelor’s degree in medicine. This article was first published on