Your gut contains a mind-boggling number of microorganisms. The human intestines is composed of ten trillion to one hundred trillion microorganisms. Its collective genome contains at least 100 times as many genes as your genome, representing a total of 500-1000 species.^1,2 The link between the gut microbiome and systemic health is irrefutable. 

Probiotics are healthy bacteria that are naturally part of the microbiome. While not all beneficial bacteria have the same effects, specific species promote healthy digestion, skin, mood, immune system, blood sugar control, and insulin, healthy weight, cholesterol, liver function and support healing leaky gut. A 2020 review of probiotics concluded, “multi-strain dietary supplements are at an advantage over single microorganisms,” because combining strains expands the range of potential benefits.³ This blog reviews some of the top health benefits of probiotics.

Mood

The pioneering research into the gut-brain axis has unlocked the profound impacts intestinal health has on mood, sleep and cognition. Microorganisms and the chemicals they produce regulate the body through a series of biochemical and functional linkages.^4,5 Because of these powerful benefits, probiotics that affect the brain are called psychobiotics.⁶

Psychobiotics effect neurotransmitters and proteins. They can produce gamma-aminobutyric acid (GABA), serotonin, glutamate, dopamine, and brain-derived neurotrophic factor (BDNF).^3,7-9 These chemicals play important roles in regulating mood, the ability to process information learning and memory. 

What the bacteria produce is specific to the strain, since not all bacteria synthesize the same chemicals. Lactobacillus plantarum and Streptococcus thermophilus can both produce serotonin.¹⁰ Other probiotic strains, such as Lactobacillus casei, Lactobacillus helveticus and Lactobacillus plantarum create dopamine.⁷ Serotonin and dopamine are your happy chemicals, and may explain how these bacteria support healthy mood. 

An early, 2011 study demonstrated that feeding mice Lactobacillus rhamnosus decreased anxiety-like and depressive-like behaviors.¹¹ Based on this and other animal studies, randomized, placebo-controlled clinical trials in humans have investigated the effects of multi-species probiotics on mood and confirmed this earlier animal study.

Clinical trials showed that even “healthy” volunteers experienced benefits of psychobiotics. A triple-blind, randomized, placebo-controlled clinical trial evaluated the effects of a multi-species probiotic blend taken for four weeks. Forty healthy participants took a total of five billion colony forming units (CFU) per day of combined Bifidobacterium lactis and Lactobacillus acidophilus, Lactobacillus brevis, Lactobacillus casei, Lactobacillus lactis, and Lactobacillus salivarius. After four weeks, rumination (persistent, negative thoughts that cause emotional distress) and aggression were significantly decreased in the group taking the probiotic compared to the control group.¹²

Another randomized, blinded, placebo-controlled clinical trial tested a different combination of probiotic strains, which included Lactobacillus fermentum, Lactobacillus rhamnosus, Lactobacillus plantarum and Bifidobacterium longum. Thirty-eight healthy volunteers took a total of four billion CFU of probiotic bacteria per day. After six weeks, there was a significant improvement in overall mood, energy and sleep, and reduction in feelings of anger and hostility, in the people taking the psychobiotics compared to placebo. Even three weeks after stopping the probiotics, mood and energy were still significantly better than in the control group.¹³ 

Other researchers have evaluated giving probiotics to people with diagnosed depression and anxiety. A 2020 review of six randomized clinical trials showed significant benefits of psychobiotics for promoting healthy mood in people with depression and anxiety. Given the published studies and overall safety of probiotics, the authors concluded that probiotics could be recommended “to enhance beneficial bacteria in the gut and to improve mood through the gut-brain axis.”¹⁴ 

Gas, bloating and discomfort

Being uncomfortable because you’re struggling with intestinal distress, or worried that you might have to leave the room because you don’t want to clear the room, is not something anyone wants to experience. And if you’re in an important meeting or on a date, it’s even worse. Unfortunately, people struggle with this all the time, especially folks with irritable bowel syndrome (IBS). 

Gas is created by gut bacteria taking the food you eat and turning it into methane gas. It can be a sign that too many unhealthy bacteria have taken up residence. Fortunately, probiotics can modify the gut microbiota, which has been shown in clinical trials to reduce flatulence, bloating, discomfort and altered bowel habits in people with IBS. A meta-analysis of 59 randomized, controlled clinical trials with 6,721 volunteers with IBS, showed significant improvements in overall symptoms, bloating, and flatulence when using probiotics.¹⁵

In a randomized, double-blind, placebo-controlled trial of 49 people with IBS, volunteers were administered a multispecies probiotic (B. longum, B. bifidum, B. lactis, L. acidophilus, L. rhamnosus, and S. thermophilus) twice daily for four weeks. The probiotic combination provided substantial relief to 68% of people who took it, compared to only 37.5% who took the placebo. Specifically, abdominal pain was reduced an incredible 75% in the probiotic group compared to those not taking the probiotic. People taking the probiotic supplements also experienced a significant 40% decrease in abdominal bloating and a 34% decrease in abdominal discomfort.¹⁶ 

A randomized double-blind placebo-controlled trial evaluated the effectiveness and safety of multi-strain probiotic in 51 adults with diarrhea-predominant irritable bowel syndrome (IBS-D). The volunteers were randomized to take five billion CFU per day of a probiotic mixture comprising different strains of bacteria from the prior study. They took Bifidobacterium. breve, Bifidobacterium longum, Bifidobacterium lactis, Lactobacillus rhamnosus, Lactobacillus paracasei, Lactobacillus acidophilus, Lactobacillus casei, Lactobacillus plantarum, and Streptococcus thermophilus. 

After eight weeks of taking the probiotic, 100% of the volunteers who initially rated their GI symptoms as severe said they were no longer severe. The number of people rating their IBS as moderate dropped by 52% and the total IBS symptom score decreased by an incredible 49%.¹⁷ These changes were significantly greater in those taking the probiotic compared to the control group. 

Immune system

Older adults are at higher risk for infections, and they die three times as often from infections compared to younger adults. For example, during the flu season about 90% of flu-related deaths occur in people older than 65.¹⁸ Flu vaccines are also not as potent in the elderly.¹⁹ Additionally, as people get older the immune system tilts towards inflammation, contributing to the illnesses that are so common we age—cancer, cardiovascular disease, stroke, arthritis, osteoporosis and dementia.²⁰

Probiotics can suppress pathogens. In fact, molecules secreted by friendly lactic-acid probiotics can reduce the prevalence and virulence of certain highly inflammatory bacteria such as Klebsiella and E. coli.²¹ A molecule secreted by the probiotic Lactobacillus salivarius prevented mice from succumbing to invasive infections caused by Listeria monocytogenes.²² 

One way in which probiotics promote a healthy immune system is by stimulating the body’s secretion of immunoglobulin A (IgA). This immune protein helps protect against gastrointestinal infections, as well as reduce allergies, modulate the expression of genes, release important natural enzymes and decrease the ability of pathogens to adhere to the intestinal wall.²³

Probiotics have even been demonstrated to improve vaccine response in adults. A review of twenty randomized controlled trials in nearly 2,000 adults who took probiotics or prebiotics found the response to flu vaccine was significantly improved over their counterparts who did not consume probiotics and prebiotics.²⁴

Blood sugar control

Poor blood sugar control and insulin resistance are hallmarks of metabolic syndrome, obesity, diabetes, heart disease, dementia and lot of other problems nobody wants. They can also cause depression, anxiety, difficulty concentrating and fatigue. 

Your gut microbiome profoundly influences blood sugar and insulin. In vitro and animal models have shown that probiotics can improve insulin resistance.²⁵ And human clinical trials have confirmed the benefit of probiotics. A meta-analysis evaluated 10 randomized clinical trials with 565 volunteers with insulin-dependent diabetes (type 2 diabetes). The data showed that at the end of the clinical trials, which lasted from four to 12 weeks, people taking the probiotics had significantly lower fasting blood sugar than the control group.²⁶

Another meta-analysis of 15 studies with 902 volunteers with type 2 diabetes concluded that those who took probiotics had lower fasting blood sugar, hemoglobin A1c (HbA1c) and insulin resistance compared to the control groups. Clinical trials evaluated in the meta-analysis supplied multi-species probiotic blends containing Lactobacillus acidophilus, Lactobacillus casei, Lactobacillus rhamnosus, Lactobacillus bulgaricus, Bifidobacterium bifidum, Bifidobacterium breve, Bifidobacterium lactis, Bifidobacterium longum, Streptococcus thermophilus.²⁷

Weight management

Given all the ways in which gut bacteria influences systemic health, it’s not surprising that probiotics promote healthy weight. The first evidence pointing to an association between obesity and intestinal microbes was produced by studies applying large-scale DNA sequencing technology to screen the entire gut microbiome.²⁸ There are many potential mechanisms to explain the microbiome’s effect on weight. However, improving insulin resistance and inflammation are likely two of the most important, and supplementing with healthy gut bacteria have been shown to promote healthy levels of both.²⁹ 

In adults, combinations of different strains of Lactobacillus and Bifidobacterium led to a significant reduction of body weight, body mass index (BMI), waist circumference, and fat mass. In a randomized, controlled clinical trial of obese postmenopausal women (ages 45-70 years old), volunteers took a probiotic blend containing nine different strains 2.5 billion CFU of Lactobacillus and Bifidobacterium or placebo for 12 weeks. At the end of the study, the women taking the probiotic supplement had lower body weight, BMI and fat mass.³⁰

Cardiovascular health

Heart disease is the leading cause of death in the United States. Someone in the U.S. dies from heart disease about every 90 seconds, killing over 375,000 people a year. Elevated cholesterol is a risk factor for heart disease and stroke. Over 93 million Americans (20 years or older) have total cholesterol levels at or above 200 mg/dL, which the Centers for Disease Control (CDC) considers too high.³¹

Some helpful Lactobacillus and Bifidobacterium species express an enzyme, called bile salt hydrolase (BSH), that interacts with cholesterol and makes it less absorbable. Instead of the cholesterol entering your blood stream, your body eliminates it in your poop, which helps explain the ability of probiotics to support healthy cholesterol levels.³² 

In a randomized double-blind controlled trial, the effects of a probiotic combination of Lactobacillus acidophilus plus Bifidobacterium bifidum were evaluated in 70 volunteers with high cholesterol. People who received the probiotic capsules took a total of six billion CFU per day of the bacteria from the supplement. The study lasted six weeks. At the end of the study, total cholesterol and low-density lipoprotein (LDL) cholesterol were significantly lower in people taking the probiotics compared to those taking in the placebo.³³ 

A systematic review of 13 clinical trials with 485 volunteers confirmed the health benefits of probiotics on cardiovascular disease risk. Total cholesterol, LDL cholesterol and triglycerides all significantly improved in the people taking the probiotics. The mean decrease in total cholesterol was 6.40 mg/dl, LDL cholesterol decreased 4.90 mg/dl and triglycerides dropped 3.95 mg/dl.³⁴ 

Liver health

Your liver controls than 300 processes in the body. It detoxifies chemicals (both synthetic and naturally occurring), metabolizes medications, produces blood clotting proteins, breaks down fat to create energy, helps ensure the amount of sugar in your blood stays constant and detoxifies ammonia in the blood so it doesn’t build up to toxic levels. 

Fatty liver is a dangerous condition that can lead to liver fibrosis, irreversible cirrhosis, liver cancer, heart disease and complications from type 2 diabetes.³⁵  The technical term is steatohepatitis. In medical speak, “steato” means fat, “hepa” means liver and “itis” means inflammation. So this condition is a combination of fat in the liver and inflammation. While alcoholics are at high risk for this, people who don’t drink excessively can also develop fatty liver. 

Non-alcoholic fatty liver, or non-alcoholic steatohepatitis (NASH) is common in Western countries. While obesity is a major risk for developing this, even up to 50% of non-obese people in the general population have NASH.³⁶ In people who are overweight, weight loss improves NASH. 

This condition damages liver cells and causes liver enzymes to leak into the blood, which are then detected in high amount on blood tests. The liver enzymes are aspartate transaminase (AST) and alanine aminotransferase (ALT). AST and ALT tests are routinely ordered during annual exams. Cholesterol and triglycerides are also commonly elevated in people with fatty liver.

Probiotics have emerged as a powerful tool for promoting liver health in people with NASH. Given their general health-promoting effects, probiotics likely also support healthy liver function in people without this condition. 

Two meta-analyses concluded that multi-strain probiotics promote liver health in people with NASH. The studies evaluated 31 randomized, controlled clinical trials with 1343 volunteers who had been diagnosed with NASH. The bacterial strains used differed between studies, but the most commonly used bacteria were B. breve, B. longum, L. acidophilus, L. paracasei, L. plantarum, L. bulgaricus, L. rhamnosus and S. thermophilus. Liver enzymes (ALT and AST), inflammation, cholesterol (total and LDL) and BMI were all  significantly improved in people taking the probiotics.^37,38 Another group of researchers that reviewed data from 26 randomized, controlled clinical trials came to the same conclusions.³⁹

Skin health

Your skin is your body’s largest organ, and probiotics have been shown to promote healthy skin in people with acne, atopic dermatitis and psoriasis. Research confirms that gut health has indirect benefits for the skin, and that probiotics can promote healthy skin by strengthening the intestinal lining, promoting healthy inflammation and immunity and by producing butyrate and other short chain fatty acids.⁴⁰ 

In healthy people the gut barrier protects us from inflammatory molecules passing into the blood stream and traveling throughout the body. However, during gut dysbiosis the intestinal lining is damaged, inflammatory molecules can reach the blood stream and create systemic inflammation, including inflammation in the skin. Fortunately, clinical trials have demonstrated that probiotics can promote a healthy gut microbiome and significantly improve skin health in people with acne, atopic dermatitis and psoriasis. 

Acne is the bane of many teenagers, but older adults are not immune to getting a flare up later in life. Acne affects 85% of adolescents and young adults (12-25 years old) in Western countries, and as many as 50% continue struggling with adult acne.^41,42

In a 2013 randomized, open-label clinical trial, researchers evaluated the effects of an oral probiotic blend of B. bifidum, L. acidophilus and L. bulgaricus on adult acne. Forty-five volunteers (18-35 years old) with adult acne who took the multistrain probiotic for 12 weeks experienced an 82% reduction in acne, which was significantly better than volunteers taking only the antibiotic.⁴³

Two additional studies evaluated the effects of taking probiotics alone. One looked at using a single probiotic species of L. rhamnosus and showed a 30% improvement in acne over 12 weeks in adults.⁴⁴ The other study, which combined L. bulgaricus and S. thermophilus for twelve weeks resulted in an up to 66% decrease in adult acne.⁴⁵

Atopic dermatitis is a chronic inflammatory condition that makes your skin red and itchy. In a randomized, placebo-controlled clinical trial, fifty children with moderate atopic dermatitis ages 4 to seventeen years old were randomized to receive either a probiotic supplement containing B. lactis, B. longum, and L. casei or placebo for twelve weeks. All volunteers continued their topical anti-inflammatory steroid medications and moisturizing cream. At the end of the study, 96% of the children taking the probiotic improved, compared to 46% in the placebo group. Using a standardized symptom scoring model for atopic dermatitis, the researchers concluded that the main symptoms score decreased by 83% in the group taking the probiotic compared to only a 24% improvement in the placebo group and topical steroid use also significantly decreased in the probiotic group compared to placebo.⁴⁶ 

Another study determined that taking a probiotic blend shifts the gut microbiome to a healthier mix of bacteria, which is associated with improved skin health.⁴⁷ Three clinical trials, each lasting 8 weeks, detected a 63-68% improvement in volunteers taking probiotics.^47-50 They used probiotics mixtures containing B. bifidum, B. breve, B. infantis, L. bulgaricus, L. casei, L. rhamnosus, L. salivarius or S. thermophilus. 

Probiotics have all shown to be helpful for people with psoriasis, another skin condition characterized by chronic inflammation. Researchers conducted a 12-week randomized, double-blind, placebo-controlled clinical trial on ninety patients with psoriasis (ages 18-70 years old). The volunteers took a probiotic supplement containing B. lactis, B. longum and L. rhamnosus or placebo. At the end of the study, nearly 67% of the volunteers taking the probiotic experienced a reduction in the Psoriasis Area and Severity Index score of at least 75%, compared to only 42% of those taking the placebo.⁵¹ Another study that provided only B. infantis for 6-8 weeks to people with psoriasis. At the end of the study there was a significant decrease in systemic inflammatory markers such as C-reactive protein (CRP) and tumor necrosis factor alpha (TNF-alpha), showing once again the probiotic dietary supplements promote healthy inflammation beyond the gut.⁵²

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