Did you know that the bacteria in your body outnumber your body's cells 10 to 1? It's true, and most of them reside in your gut.
But there really is no need to panic, most bacteria are quite harmless.
Having the right bacteria in there has even been linked to numerous health benefits (1).
This includes weight loss, improved digestion, enhanced immune function, better skin and a reduced risk of many diseases (2).
This leads us to the topic at hand, probiotics.
Probiotics are foods or supplements that contain these friendly bacteria, and are supposed to help colonize our guts with health-boosting microorganisms.
The importance of this can not be overstated.
Taking care of your gut, and the friendly bacteria that reside there, may be one of the single most important things you can do for your health.
According to the official definition, probiotics are "live microorganisms that, when administered in adequate amounts, confer a health benefit on the host" (3).
Probiotics are usually bacteria, but there is also a type of yeast that can function as a probiotic.
You can get probiotics from supplements, as well as foods that are prepared by bacterial fermentation.Probiotic foods include yogurt, kefir, sauerkraut, tempeh, kimchi and others. Probiotics should not be confused with prebiotics (note the "e"), which are dietary fibers that help feed the friendly bacteria that are already in the gut ( 4).
There are actually dozens of different probiotic bacteria that have been shown to have health benefits.
The most common groups include Lactobacillus and Bifidobacterium. Then there are many different species within each group, and each species has many strains.
Interestingly, different probiotics seem to work for different health conditions. Therefore, choosing the right type (or types) of probiotic is essential.
Many probiotic supplements combine different species together in the same supplement. These are known as broad-spectrum probiotics, or multi-probiotics.
Keep in mind that this is a new but rapidly expanding area of research.
Although the evidence is promising, it is not conclusively proven that probiotics help with all the health conditions mentioned in this article (5).
Bottom Line: Probiotics are live microorganisms that cause health benefits when consumed in adequate amounts. There are many different types, and you can get them from foods or supplements.
The complex community of microorganisms in your gut is called the gut flora (6).
Your gut actually contains hundreds of different types of microorganisms, with some numbers going as high as 1000.
This includes bacteria, yeasts and viruses. The great majority is bacteria.
Most of the gut flora is found in the colon, or large intestine, the last part of the digestive tract.
The metabolic activities of the gut flora actually resemble those of an organ. For this reason, some scientists refer to the gut flora as the "forgotten organ" (7).
The gut flora actually performs many functions that are important for health. It manufactures vitamins, including vitamin K and some of the B vitamins (8).
However, not all organisms in the gut are friendly. Some are good, others are bad.
Probiotics (and prebiotic fibers) can help correct this balance, making sure that our "forgotten organ" is functioning optimally (21).
Bottom Line: Your gut flora consists of hundreds of different types of microorganisms. Probiotics help your gut flora perform optimally.
Probiotics have been studied most in regard to digestive health (22).The strongest evidence has to do with antibiotic-associated diarrhea.
When people take antibiotics, especially for long periods of time, they often suffer from diarrhea for a long time after the infection has been eradicated.
This is because the antibiotics kill many of the natural bacteria in the gut, which shifts the balance and allows the "bad" bacteria to thrive.
Probiotics have also been shown to be beneficial against irritable bowel syndrome, a very common digestive disorder. They can help reduce gas, bloating, constipation, diarrhea and other symptoms (26, 27, 28).
Some studies also show that probiotics may be beneficial against inflammatory bowel diseases such as Crohn's disease and ulcerative colitis (29).
If you currently have digestive problems that you can't seem to get rid of, then perhaps a probiotic supplement is something you should consider.
Bottom Line: Probiotics have been shown to be effective against various digestive problems. This includes antibiotic-associated diarrhea and irritable bowel syndrome.
Obese people have different gut bacteria than lean people (34).
The most impressive study on this was published in 2013. It was a study of 210 individuals with central obesity (lots of fat in the belly area).
In this study, taking the probiotic Lactobacillus gasseri caused people to lose 8.5% of their belly fat mass over a period of 12 weeks (40).
When they stopped taking the probiotic, they gained the belly fat back within 4 weeks.
There is also some evidence that Lactobacillus rhamnosus and Bifidobacterium lactis can help with weight loss and obesity prevention (41).
However, this needs to be studied more before any recommendations can be made.
There are also some animal studies showing that other probiotic strains could even lead to weight gain, not loss (42).
Here's an article with more info about the weight loss effects of probiotics.
Bottom Line: There is some evidence that the certain probiotic strains can help people lose weight, but this needs to be studied a lot more.
Getting into all the incredible benefits of probiotics is beyond the scope of this article.
However, there are a few that are definitely worth highlighting here:
- Inflammation: Probiotics have been shown to 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 LDL cholesterol levels (46, 47).
- Blood pressure: Probiotics have also been shown to cause modest reductions in blood pressure (48, 49).
- Immune function: Several probiotic strains can enhance immune function and lead to reduced risk of infections, including 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).
For more details, here are the top 8 health benefits of probiotics.
Bottom Line: Probiotics have been shown to have numerous health benefits. They may reduce depression and anxiety, improve heart health and enhance immune function, to name a few.
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. This includes gas and mild abdominal discomfort (53).
After this initial adaptation period is over, your digestion should be better than it was before.
In people with compromised immune systems, probiotics can lead to dangerous infections. This includes people with HIV, AIDS and several other conditions (54).
If you have a medical condition, definitely consult with your doctor before taking a probiotic supplement.
Bottom Line: Probiotic supplements may cause digestive symptoms, but this should subside within a few days. They may be dangerous for people with certain medical conditions.
Maintaining a healthy gut goes way beyond just taking a probiotic supplement.
What you do from day to day is just as important, since all sorts of lifestyle factors have been shown to affect your gut bacteria.