Probiotics are live microorganisms that can be consumed through fermented foods or supplements (1).
More and more studies show that the balance or imbalance of bacteria in your digestive system is linked to overall health and disease.
Probiotics promote a healthy balance of gut bacteria and have been linked to a wide range of health benefits.
This is an overview of the key health benefits linked to probiotics.
These benefits are thought to result from the ability of probiotics to restore the natural balance of gut bacteria (4).
An imbalance means there are too many bad bacteria and not enough good bacteria. It can happen due to illness, medication such as antibiotics, poor diet and more.
Consequences can include digestive issues, allergies, mental health problems, obesity and more (5).
Probiotics are usually found in fermented foods or taken as supplements. What's more, they appear to be safe for most people.
Bottom Line: Probiotics are live microorganisms. When taken in sufficient amounts, they can help restore the natural balance of gut bacteria. As a result, health benefits may follow.
Probiotics are widely known for their ability to prevent diarrhea or reduce its severity.
Diarrhea is a common side effect of taking antibiotics. It occurs because antibiotics can negatively affect the balance of good and bad bacteria in the gut (6). Several studies suggest probiotic use is associated with a reduced risk of antibiotic-associated diarrhea (7, 8, 9).
In one study, researchers found that taking probiotics reduced antibiotic-associated diarrhea by 42% (10).
Probiotics can also help with other forms of diarrhea not associated with antibiotics.
A large review of 35 studies found certain strains of probiotics can reduce the duration of infectious diarrhea by an average of 25 hours (11).
Probiotics reduced the risk of travelers' diarrhea by 8%. They also lowered the risk of diarrhea from other causes by 57% in children and 26% in adults (12).
Effectiveness varies, depending on the type and dose of the probiotic taken (13).
Bottom Line: Probiotics can reduce the risk and severity of diarrhea from a number of different causes.
Both animal and human studies find that probiotic supplements can improve some mental health disorders (15).
A review of 15 human studies found supplementing with Bifidobacterium and Lactobacillus strains for 1–2 months can improve anxiety, depression, autism, obsessive-compulsive disorder (OCD) and memory (15).
One study followed 70 chemical workers for 6 weeks. Those who consumed 100 grams of probiotic yogurt per day or took a daily probiotic capsule experienced benefits for general health, depression, anxiety and stress (16).
Benefits were also seen in a study of 40 patients with depression.
Taking probiotic supplements for 8 weeks decreased depression levels and reduced levels of C-reactive protein (a marker of inflammation) and hormones such as insulin, compared to people who did not take a probiotic (17).
Bottom Line: Research shows taking probiotics may help improve symptoms of mental health disorders such as depression, anxiety, stress and memory, among others.
Probiotics may help keep your heart healthy by lowering LDL ("bad") cholesterol and blood pressure.
Certain lactic acid-producing bacteria may reduce cholesterol by breaking down bile in the gut (18).
Bile, a naturally occurring fluid mostly made of cholesterol, helps digestion.
By breaking down bile, probiotics can prevent it from being reabsorbed in the gut, where it can enter the blood as cholesterol (19).
A review of 5 studies found that eating a probiotic yogurt for 2–8 weeks reduced total cholesterol by 4% and LDL cholesterol by 5% (20).
Another study conducted over 6 months found no changes in total or LDL cholesterol. However, the researchers did find a small increase in HDL ("good") cholesterol (21).
Consuming probiotics may also lower blood pressure. A review of 9 studies found that probiotic supplements reduce blood pressure, but only modestly (22).
In order to experience any benefits related to blood pressure, supplementation had to exceed 8 weeks and 10 million colony-forming units (CFUs) daily (22).
Bottom Line: Probiotics may help protect the heart by reducing "bad" LDL cholesterol levels and modestly lowering blood pressure.
Certain probiotic strains may reduce the severity of eczema in children and infants.
One study found eczema symptoms improved for infants fed probiotic-supplemented milk, compared to infants fed milk without probiotics (23).
Some probiotics may also reduce inflammatory responses in people with milk or dairy allergies. However, the evidence is weak and further studies are needed (27).
Bottom Line: Probiotics may reduce the risk and severity of certain allergies, such as eczema in infants. However, more research is needed.
Over one million people in the US suffer from inflammatory bowel disease, including ulcerative colitis and Crohn's disease (28).
Certain types of probiotics from the Bifidobacterium and Lactobacillus strains have improved symptoms in people with mild ulcerative colitis (29).
Surprisingly, one study found that supplementing with the probiotic E. coli Nissle was just as effective as drugs in maintaining remission in people with ulcerative colitis (30).
However, probiotics appear to have little effect on symptoms of Crohn's disease (31).
Nevertheless, probiotics may have benefits for other bowel disorders. Early research suggests they may help with symptoms of irritable bowel syndrome (IBS) (32).
They have also been shown to reduce the risk of severe necrotizing enterocolitis by 50%. This is a fatal bowel condition that occurs in premature infants (33).
Bottom Line: Probiotics may help reduce the symptoms of bowel disorders like ulcerative colitis, IBS and necrotizing enterocolitis.
Probiotics may help give your immune system a boost and inhibit the growth of harmful gut bacteria (34).
Also, some probiotics have been shown to promote the production of natural antibodies in the body. They may also boost immune cells like the IgA-producing cells, T lymphocytes and natural killer cells (35, 36).
A large review found that taking probiotics reduced the likelihood and duration of respiratory infections. However, the quality of the evidence was low (37).
Another study including over 570 children found that taking Lactobacillus GG reduced the frequency and severity of respiratory infections by 17% (38).
The probiotic Lactobacillus crispatus has also been shown to reduce the risk of urinary tract infections (UTIs) in women by 50% (39).
Bottom Line: Probiotics may help boost your immune system and protect against infections.
For example, some probiotics prevent the absorption of dietary fat in the intestine.
They may also help with weight loss directly. In one study, dieting women who took Lactobacillus rhamnosus for 3 months lost 50% more weight than women who didn't take a probiotic (45).
However, it's important to be aware that not all probiotics aid in weight loss.
Surprisingly, some studies found certain probiotics, such as Lactobacillus acidophilus, can even lead to weight gain (47).
More studies are needed to clarify the link between probiotics and weight (48).
Bottom Line: Certain probiotics may help you lose weight and belly fat. However, other strains have been linked to weight gain.
You can get probiotics from a variety of foods or supplements.
Live probiotic cultures are often found in fermented dairy products such as yogurts and milk drinks. Fermented foods like pickled vegetables, tempeh, miso, kefir, kimchi, sauerkraut and soy products may also contain some lactic acid bacteria.
You can also take probiotics as tablets, capsules and powders that contain the bacteria in dried form.
However, be aware that some probiotics can be destroyed by stomach acid before they even reach the gut — meaning that you get none of the intended benefits.
If you want to experience any of the health benefits discussed above, it's important that you consume adequate amounts.
Most of the studies showing benefits used dosages of 1 billion to 100 billion live organisms or colony-forming units (CFU) per day.