For Cereally?

The Claim

You should take probiotic pills or eat probiotic foods for a healthy gut.

Initial search

What exactly are probiotics? According to WebMD, probiotics are live bacteria and yeasts that are good for you and your digestive system. Everyone has bacteria in their lower digestive tract. In fact, there are more bacteria in your intestines than cells in your body! Everyone has both “good” and “bad” bacteria. In healthy people, the good bacteria are able to keep the bad bacteria in check. However, sometimes the good bacteria can be killed off, allowing the bad bacteria to take over and cause problems ranging from diarrhea and constipation to weight gain and skin conditions.

In order to help people maintain an optimal bacteria balance, some doctors recommend supplementing with probiotics, or “good” bacteria. Probiotics are available in pill form, and can also be found in fermented foods such as certain dairy products, sauerkraut, kimchi, and kombucha.

There are many types of probiotics and products available. Some claim to contain more than 100 billion live bacteria (called colony-forming units or CFUs) in each pill while others claim numbers in the millions. Some need to be refrigerated and others don’t. Some might get destroyed by stomach acid while others might not. Some were made in labs and have detailed information about genus, species, and strain while others were made in your neighborhood hippie’s backyard.

The science around gut bacteria has really gotten underway in the past decade, but there is still a lot of gray area and a lot we don’t know. This has made probiotic supplementation a controversial topic. Should everyone take a probiotic? How much do we need? Which strains? Which conditions can they help and how? Some researchers think they have answers to these questions while others are more hesitant.

Some claims made by those who support probiotic supplementation include:

They help with weight management
They treat and prevent diarrhea and constipation as well as other gut disorder such as Crohn’s disease, IBS, ulcerative colitis, and necrotizing enterocolitis
They can improve mental health conditions including: anxiety, depression, autism, obsessive-compulsive disorder, and memory via the gut-brain connection
They can help regulate insulin, and reduce inflammation, blood pressure and LDL
They can reduce symptoms of allergies and eczema
They improve sperm motility
Decrease tooth decay and gum disease
They can “boost your immune system” to decrease your chances of getting respiratory infections and urinary tract infections
They help prevent cancer

What the skeptics say:

The current research only supports treatment for certain types of diarrhea (such as that caused by antibiotics). And scientists still aren’t exactly sure how that works.
We don’t really know how much you need or which strains work best for which diseases.
We don’t really know why they seem to work for some people and not others.
They might actually cause problems for people with weak immune systems.
Probiotics have been shown NOT to change the composition of bacteria in fecal matter in healthy people
Enthusiasm for probiotics has outpaced the scientific evidence.
Until we know more, probiotics are a waste of money.

Peer reviewed research

Or click here to skip the research.

First, I conducted a search of meta-analyses of RCTs. These were all done in the past 5 years using human participants.

1. Probiotics for Gastrointestinal Conditions: A Summary of the Evidence. (2017) https://www.ncbi.nlm.nih.gov/pubmed/28762696

This summary of the evidence states that certain probiotics are effective for: acute infectious diarrhea, antibiotic-associated diarrhea, Clostridium difficile- associated diarrhea, hepatic encephalopathy, ulcerative colitis, irritable bowel syndrome, functional gastrointestinal disorders, and necrotizing enterocolitis. It states they are not effective for: acute pancreatitis and Crohn disease.

2. The role of probiotics in prevention of oral diseases. (2016) https://www.ncbi.nlm.nih.gov/pubmed/27594560

This review concluded that certain probiotics can help prevent cavities, gum disease, and bad breath.

3. Probiotics in dermatologic practice. (2016) https://www.ncbi.nlm.nih.gov/pubmed/26707956

This review looked at all the data surrounding probiotic use for skin conditions. They found enough evidence to recommend probiotic treatment for atopic dermatitis. They mentioned other conditions which needed further research.

4. Probiotics-mediated suppression of cancer. (2017) https://www.ncbi.nlm.nih.gov/pubmed/27792053

Researchers concluded that the data for using probiotics in cancer treatment is encouraging, but insufficient to recommend their use as an alternative therapy.

5. Clinical Uses of Probiotics. (2016) https://www.ncbi.nlm.nih.gov/pubmed/26844491

This review concluded that the data supports probiotic use for GI-related illnesses, but not for most other conditions. The article goes into depth regarding probiotic strains and compositions.

6. Probiotics for managing caries and periodontitis: Systematic review and meta-analysis. (2016) https://www.ncbi.nlm.nih.gov/pubmed/26965080

This review concluded that probiotics may help reduce or prevent gum disease, but the evidence for preventing and treating cavities is insufficient.

7. Systematic review: probiotics for functional constipation in children. (2017) https://www.ncbi.nlm.nih.gov/pubmed/28762070

This review found that probiotics had little on constipation in children.

8. Probiotics for the prevention of Clostridium difficile-associated diarrhea in adults and children. (2017) https://www.ncbi.nlm.nih.gov/pubmed/29257353

This review of the evidence supports probiotic treatment for people at risk for C-diff associated diarrhea.

9. Effectiveness of probiotics in irritable bowel syndrome: Updated systematic review with meta-analysis. (2015) https://www.ncbi.nlm.nih.gov/pubmed/25780308

This review found that probiotics reduce pain and severity of symptoms in many people with IBS.

10. Probiotics for weight loss: a systematic review and meta-analysis. (2015) https://www.ncbi.nlm.nih.gov/pubmed/26032481

This review found that RCTs generally do not support the use of probiotics to assist in weight loss. No significant differences were found in treatment versus control groups.

11. Probiotics and Subclinical Psychological Symptoms in Healthy Participants: A Systematic Review and Meta-Analysis. (2017) https://www.ncbi.nlm.nih.gov/pubmed/27841940

This review included 7 randomized placebo controlled clinical trial which tested whether probiotics could improve depression, anxiety, and stress. They concluded that probiotics significantly improved psychological symptoms in healthy adults.

12. Effect of Probiotics on Depression: A Systematic Review and Meta-Analysis of Randomized Controlled Trials. (2016) https://www.ncbi.nlm.nih.gov/pubmed/27509521

This review included 12 RCTs and found that probiotics significantly reduced symptoms of depression in people under age 60, but not in older adults.

13. Efficacy of probiotics on anxiety-A meta-analysis of randomized controlled trials. (2018) https://www.ncbi.nlm.nih.gov/pubmed/29995348

This meta-analysis included 12 RCTs which, together, showed no significant difference between treatment and placebo groups.

Next, I conducted a search on randomized controlled clinical trials completed in the past 5 years using humans. Some of these may have been cited in the meta-analyses above.

1.Probiotics prevent Hirschsprung’s disease-associated enterocolitis: a prospective multicenter randomized controlled trial. (2015) https://www.ncbi.nlm.nih.gov/pubmed/25370155

This RCT showed that treatment with probiotics significantly improved enterocolitis (inflammation of the small and large intestine) in children with Hirschsprung’s disease (a disease involving missing nerve cells of the colon and severe difficulty passing stool).

2. A randomized controlled trial to test the effect of multispecies probiotics on cognitive reactivity to sad mood. (2015) https://www.ncbi.nlm.nih.gov/pubmed/25862297

This RCT showed that healthy people who supplemented with a specific multi-strain probiotic for 4 weeks had a reduction in “rumination” and “aggressive thoughts” as compared to a healthy control group. The authors suggested that that this warrants research for using probiotics to treat depression.

3. Effect of multispecies probiotics on irritable bowel syndrome: a randomized, double-blind, placebo-controlled trial. (2014) https://www.ncbi.nlm.nih.gov/pubmed/23829297

This RCT showed that a specific multi-strain probiotic significantly improved IBS symptoms. After 4 weeks, 68% of the treatment group reported relief while only 37.5% of the placebo group reported relief. They also showed changes in fecal bacteria in the treatment group.

4. Influence of a combination of probiotics on bacterial infections in very low birthweight newborns. (2015) https://www.ncbi.nlm.nih.gov/pubmed/26373743

This RCT compared 80 premature infants (under 33 weeks gestation). Half received a special combination of probiotics and half did not. In the treatment group, there were about half as many late-onset septic events and half as many late-onset infections as in the control group. Also, on average, the babies who received probiotics were discharged from the NICU earlier than those who did not.

5. The effect of probiotics on serum levels of cytokine and endotoxin in peritoneal dialysis patients: a randomised, double-blind, placebo-controlled trial. (2015) https://www.ncbi.nlm.nih.gov/pubmed/25609654

This RCT showed that a 6 month probiotic treatment significantly helped dialysis patients maintain kidney function and reduce inflammation compared to the control group. I was unable to determine how significant the differences between groups were.

6. Effect of multi-strain probiotics (multi-strain microbial cell preparation) on glycemic control and other diabetes-related outcomes in people with type 2 diabetes: a randomized controlled trial. (2017) https://www.ncbi.nlm.nih.gov/pubmed/26988693

136 participants with type 2 diabetes participated in a RCT to determine whether a specific multi-strain probiotic taken over 12 weeks could help control fasting insulin and HbA1c (average blood sugar). Researchers found the probiotics to be modestly useful. The effect did not reach clinical significance for HbA1c, but did for fasting insulin.

7. The Role of Probiotics in the Treatment of Dysentery: a Randomized Double-Blind Clinical Trial. (2017) https://www.ncbi.nlm.nih.gov/pubmed/28321826

This RCT looked at how probiotics worked to help treat dysentery. The treatment group received a 7-strain probiotic for 5 days. They had significantly less time in the hospital and a shorter duration of bloody stools as compared to the control group. The effects were significant, but modest.

8. The Effect of Probiotics on Gut Microbiota during the Helicobacter pylori Eradication: Randomized Controlled Trial. (2016) https://www.ncbi.nlm.nih.gov/pubmed/26395781

This RCT showed that H-pylori patients who received probiotics along with their antibiotic treatment had better success and reduced antibiotic-resistant gut bacteria.

9. Probiotics reduce psychological stress in patients before laryngeal cancer surgery. (2016) https://www.ncbi.nlm.nih.gov/pubmed/24571169

This was a small study with only 20 patients who were randomly assigned to the treatment or control group. Researchers found that the patients treated with probiotics scored much lower on an anxiety test than the control group before they were to have surgery for laryngeal cancer.

10. Effects of continuous use of probiotics before liver transplantation: A randomized, double-blind, placebo-controlled trial. (2017) https://www.ncbi.nlm.nih.gov/pubmed/28506447

This study divided 90 liver transplant patients into treatment and control groups. They found that the patients who were treated with probiotics prior to surgery had a much lower risk of infection after liver transplant. 90 days after surgery, only 5% of the treatment group had gotten an infection whereas almost 50% of the control group did.

11. Randomized controlled trial of probiotics after colonoscopy. (2017) https://www.ncbi.nlm.nih.gov/pubmed/26183594

This RCT showed that probiotics modestly helped patients recover after colonoscopy. The treatment group reported pain for about 2 days after surgery while the control group reported pain for about 3 days.

12. Effect of probiotics on postoperative quality of gastric bypass surgeries: a prospective randomized trial. (2016) https://www.ncbi.nlm.nih.gov/pubmed/26499352

This RCT looked at whether probiotic treatment could help GI symptoms after gastric bypass. 60 patients were divided into 3 groups: Probiotic A, Probiotic B, or digestive enzyme. Results were the same for all 3 groups. Their GI symptoms improved modestly after 2 weeks of any treatment. This study could not show that probiotics worked better than digestive enzymes.

13. Probiotics prevent hepatic encephalopathy in patients with cirrhosis: a randomized controlled trial. (2014) https://www.ncbi.nlm.nih.gov/pubmed/24246768

This RCT compared 160 cirrhosis patients. The treatment group received probiotics for approximately 40 weeks while the control group did not. In that time, 7 patients in the probiotic group and 14 patients in the control group developed hepatic encephalopathy (brain damage caused by cirrhosis of the liver). Researchers concluded that the probiotics helped reduce hepatic encephalopathy.

14. Probiotics and prebiotic fiber for constipation associated with Parkinson disease: An RCT. (2016) https://www.ncbi.nlm.nih.gov/pubmed/27543643

This RCT consisted of a treatment group (80 people) and a control group (40 people) who had constipation associated with Parkinson’s disease. The treatment group consumed fermented milk with pre and probiotics daily. After 4 weeks, the treatment group had significantly fewer constipation symptoms than the control group.

15. Probiotics and Child Care Absence Due to Infections: A Randomized Controlled Trial. (2017) https://www.ncbi.nlm.nih.gov/pubmed/28674113

This RCT included 290 healthy children ages 8-14 months. Half were given a multi-strain probiotic for 6 months. At the end of the study, there was no difference in outcomes. Children who took probiotics were just as likely to get sick and need to be kept home as the control children.

16. Effects of fiber and probiotics on diarrhea associated with enteral nutrition in gastric cancer patients: A prospective randomized and controlled trial. (2017) https://www.ncbi.nlm.nih.gov/pubmed/29069041

This RCT divided 120 patients undergoing gastric cancer surgery into 3 groups: fiber-free, fiber-enriched, and fiber plus probiotic enriched. After 7 days, people in the fiber plus probiotic group had significantly reduce diarrhea and other intestinal disorders compared with the other groups.

17. Effect of probiotics on the incidence of ventilator-associated pneumonia in critically ill patients: a randomized controlled multicenter trial. (2016) https://www.ncbi.nlm.nih.gov/pubmed/27043237

This RCT evaluated 235 adults who were to receive mechanical ventilation for more than 48 hours. 36% of the treatment group acquired ventilator-associated pneumonia versus 50% of controls. Additionally, only 24% of the treatment group acquired pathogenic microorganisms whereas 44% of the control group did.

18. Probiotics (Lactobacillus gasseri KS-13, Bifidobacterium bifidum G9-1, and Bifidobacterium longum MM-2) improve rhinoconjunctivitis-specific quality of life in individuals with seasonal allergies: a double-blind, placebo-controlled, randomized trial. (2017) https://www.ncbi.nlm.nih.gov/pubmed/28228426

This study divided 173 people with seasonal allergies into either the treatment or placebo group. After 8 weeks, the treatment group was experiencing significantly reduced allergy symptoms and improved quality of life.

19. Yogurt supplemented with probiotics can protect the healthy elderly from respiratory infections: A randomized controlled open-label trial. (2017) https://www.ncbi.nlm.nih.gov/pubmed/28848330

205 volunteers age 45+ were divided into treatment and control groups. After 12 weeks, researchers determined that the risk of getting an upper respiratory tract infection was cut almost in half by taking probiotics.

20. Effect of probiotics on vaginal health in pregnancy. EFFPRO, a randomized controlled trial. (2016) https://www.ncbi.nlm.nih.gov/pubmed/27342046

Researchers wanted to determine whether probiotic food supplements could maintain or restore normal vaginal microbiota during pregnancy. 320 pregnant women participated. The treatment group received probiotics during their first trimester. No significant differences were seen between groups.

What We Know and Don’t Know

Probiotics is a topic where there is a lot we still don’t know. The research I found is very promising, but also very incomplete. I could dedicate an entire blog to probiotic treatment for each condition for which they have been studied. Here, I will try to summarize my findings in a table. I’ll assign an efficacy category to each condition (Effective and well-studied, seems somewhat effective, or probably not effective) based on my research above. However, the 30 works I’ve cited may or may not represent the majority of the data (hopefully they come close). These were simply the most relevant reviews and clinical trials I found in my non-exhaustive search of Pub-Med abstracts.

Acute infectious diarrhea	Effective, well studied
Antibiotic-associated diarrhea	Effective, well studied
Clostridium difficile- associated diarrhea	Effective, well studied
Hepatic encephalopathy	Effective, well studied
Ulcerative colitis	Effective, well studied
Irritable bowel syndrome	Effective, well studied
Functional gastrointestinal disorders	Effective, well studied
Necrotizing enterocolitis	Effective, well studied
Acute pancreatitis	Probably not effective
Crohn disease	Probably not effective
Atopic dermatitis	Effective, well studied
Dental caries	Probably not effective
Gingivitis	Effective, well studied
Cancer	May be somewhat effective, not well studied
Constipation in children	Probably not effective
Weight loss	Probably not effective
Depression and Anxiety	Found conflicting meta-analyses
Kidney function in dialysis patients	Seems somewhat effective
Fasting insulin in diabetes patients	Seems somewhat effective
Dysentery	Effective, well studied
H-Pylori	Effective, well studied
Infection after liver transplant	Seems somewhat effective
GI symptoms after gastric bypass	Seems somewhat effective
Constipation associated with Parkinson’s	Seems somewhat effective
GI symptoms after cancer surgery	Seems somewhat effective
As a preventative in healthy infants	Probably not effective
Ventilator associated pneumonia	Seems somewhat effective
Seasonal allergies	Seems somewhat effective
Upper respiratory tract infection in ages 45+	Seems somewhat effective
Maintain healthy vaginal flora during pregnancy	Probably not effective

Conclusions and applications

Each condition needs more research to determine exact strains and doses, whether probiotic foods are as effective as pills, and why treatments may work for some patients and not others.

As you can see from the table, probiotics have the best marks for GI related problems. Even for those, however, probiotics aren’t entirely understood.

Surprisingly, I did not find much research where healthy participants were studied using probiotics as a means to prevent illness or maintain health. The only study with truly healthy participants was the infant study, which found no differences between the treatment and control groups. This leads me to believe that probiotics are not a good idea at this time as an everyday supplement, especially since we have no guidance for which kinds and how much to take.

On the other hand, probiotics seem to be at least somewhat useful for a broad spectrum of illnesses and they don’t have many side effects for generally healthy people. There would be no physical harm for most people to take or eat probiotics just maybe to be on the safe side. I wouldn’t go spending a fortune though.

If you have a condition and are wondering whether to try a probiotic for treatment, I would highly recommend going straight to the peer reviewed research. Look for RCTs that have used probiotics for your specific condition. Since there is a lot we still don’t know about probiotics, it’s easy for supplement companies to promote unproven hypotheses for why and how they work or to cherry-pick studies. This is an area where you really need to consult the research instead of top websites.

I’m personally excited to see how much research is going into probiotics. We are slowly but surely figuring out the microbiome and how to help our little bugs improve our health.