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Probiotics 101: A Simple Beginner’s Guide

Kris Gunnars
Jan 9 2019

Yogurt is one delicious way to get probiotics to help your gut flora flourish. (Brenda Godinez/Unsplash)
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 (
1, 2).
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 (
They’re usually bacteria, but certain types of yeasts can also function as probiotics.
You can get probiotics from supplements, as well as from foods prepared by bacterial fermentation.

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. Cabbage kimchi, sauerkraut sour glass jars over the rustic kitchen table.
Dozens of different probiotic bacteria offer health benefits.

The most common groups include Lactobacillus and Bifidobacterium. Each group comprises different species, and each species has many strains.
Full fruit and Greek yogurt breakfast bowl. Persimmon, apple, walnuts, pomegranates and natural yogurt. Healthy food concept on a light background, top view.
Interestingly, different probiotics address different health conditions. Therefore, choosing the right type—or types—of probiotics is essential.
Some supplements—known as broad-spectrum probiotics or multi-probiotics—combine different species in the same product.
Although the evidence is promising, more research is needed on the health benefits of probiotics (

Importance of Microorganisms for Your Gut
The complex community of microorganisms in your gut is called the gut flora or microbiota (
In fact, your gut contains hundreds of different types of microorganisms—as many as 1,000, according to some estimations.
This includes bacteria, yeasts and viruses—with bacteria making up the vast majority.
Most of the gut flora is found in your colon, or large intestine, which is the last part of your digestive tract.
Surprisingly, the metabolic activities of your gut flora resemble those of an organ. For this reason, some scientists refer to the gut flora as the “forgotten organ” (
Your gut flora performs many functions that are important for health. It manufactures vitamins, including vitamin K and some of the B vitamins (
It also turns fibers into
short-chain fats like butyrate, propionate, and acetate, which feed your gut wall and perform many metabolic functions (9, 10).
These fats also stimulate your immune system and strengthen your gut wall. This can help prevent unwanted substances from entering your body and provoke an immune response (
11, 12, 13, 14).
However, not all organisms in your gut are friendly.
Your gut flora is highly sensitive to your diet, and studies show that
unbalanced gut flora is linked to numerous diseases (15, 16).
These diseases include obesity, type 2 diabetes, metabolic syndrome, heart disease, colorectal cancer, Alzheimer’s and depression (
17, 18, 19, 20).
Probiotics—and prebiotic fibers—can help correct this balance, ensuring that your “forgotten organ” is functioning optimally (

Impact on Digestive Health
Probiotics are widely researched for their effects on digestive health (
Strong evidence suggests that probiotic supplements can help cure antibiotic-associated diarrhea (
23, 24, 25).
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 (26, 27, 28).
Some studies also note benefits against inflammatory bowel diseases, such as Crohn’s disease and ulcerative colitis (
What’s more, probiotics may fight Helicobacter pylori infections, which are one of the main drivers of ulcers and stomach cancer (
30, 31, 32, 33).
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 (
Interestingly, animal studies indicate that fecal transplants from lean animals can make obese animals lose weight (
35, 36).
Therefore, many scientists believe that your gut bacteria are important in determining body weight (
37, 38).
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 (
Conversely, some animal studies demonstrate that other probiotic strains could lead to weight gain, not loss (

Other Health Benefits
There are many
other benefits of probiotics. They affect:
  • Inflammation: Probiotics reduce systemic inflammation, a leading driver of many diseases (43).
  • Depression and anxiety: The probiotic strains Lactobacillus helveticus and Bifidobacterium longum have been shown to reduce symptoms of anxiety and depression in people with clinical depression (44, 45).
  • Blood cholesterol: Several probiotics have been shown to lower total and “bad” LDL cholesterol levels (46, 47).
  • Blood pressure: Probiotics may also cause modest reductions in blood pressure (48, 49).
  • Immune function: Several probiotic strains may enhance immune function, possibly leading to a reduced risk of infections, including for the common cold (50, 51).
  • Skin health: There is some evidence that probiotics can be useful for acne, rosacea and eczema, as well as other skin disorders (52).
This is only a small slice of probiotics’ total benefits, as ongoing studies indicate a wide breadth of health effects.

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 (
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 (
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.
However, probiotic supplements offer a wide range of benefits with few side effects — so if you’re interested in improving your gut health, they could be worth a shot.

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