Probiotics are tiny, but the big attention they have attracted has many people wondering if probiotics are good for you. Here are 5 science-backed facts you should know about probiotics, including answers to some of your biggest questions. Put these microscopic organisms under the lens, and let’s see what the scientific literature is saying about whether you should take a probiotic, how much is best, and which are the most helpful strains.
FACT: By definition, a probiotic is proven to offer health benefits to the host.
The word probiotic comes from the Latin word ‘pro’ (which means for), and the Greek word ‘biotikos’ (which means life). It was Elias Metchnikoff in 1900 who first developed the idea that microorganisms are beneficial for human health. He proposed that aging is caused by toxic bacteria in the gut, while lactic acid, producing good bacteria could prolong life. It was ground-breaking at the time and inspired others to investigate the relationships our bodies have with the bacteria and yeast that live on and in us. Today, the definition of a probiotic is a live micro-organism which when administered in adequate amounts confers a health benefit to the host. In other words, if you have enough of these helpful lactic acid bacteria or yeasts in your body, it’s good for your health.
The dynamic community of micro-organisms that live in your intestine is called the gut microbiota (formerly called the gut flora). There are complex interactions happening between your gut and the 100 billion micro-organism community you find there. Since your gut is the primary interface between you and the external world (the food you ingest), it’s important that it’s functioning optimally.
FACT: Probiotics are transient guests that pass through your gut offering beneficial effects.
Probiotics are good for you in many ways. Probiotics support human health by helping your gut resist the growth of pathogenic micro-organisms while restoring and maintaining the beneficial micro-organisms. Some probiotics help breakdown the food you’ve eaten, enhance gut barrier function, improve absorption of nutrients, help gut motility (e.g. pleasant visits to the porcelain throne), and interact with your gut’s cells to promote healthy immune reactions, as well as the gut-brain axis influencing your mood.
It’s important that any fluctuations in your gut’s inhabitants maintain their balance – if there are too many opportunistic pathogenic bacteria at any given time, the health of the gut declines. You’ll feel it: gas, bloating, indigestion, diarrhea, constipation, low immunity, poor mood, etc. Fluctuations in which microorganisms are in your gut’s microbiota can occur more frequently than you realize, particularly under stress, dietary changes, illness, use of certain medications, pregnancy, aging, and more. A growing body of evidence shows that probiotic supplementation can help restore the balance in the gut microbiota. In particular, a large study published in the scientific journal, Gut Microbes, involving 1413 people, revealed the use of antibiotics is associated with a long-term shift (up to 4 years in some individuals) in the composition of the gut microbiota. Of note, another review suggests probiotic consumption may reduce acute infections and thus the need for antibiotics.
FACT: Probiotic supplementation helps restore gut microbiota balance after antibiotic use.
Your purpose for taking a probiotic will determine the dose. Use efficacious studies as a guide to help you. Check the CFU (colony forming unit) used in such a study to help you determine an ideal dosage. A CFU is a measurement of how many of the little microbes are likely to grow to form a colony in the gut. When choosing a probiotic supplement, look for manufacturers that list the total number of CFUs on the label, ideally by strain, and state the amount that will be there at the date of expiry (use by date), not the date of manufacturing. Why? There’s a decline in CFUs in a product as it sits on the shelf, which should be taken into account when the manufacture made the product.
It’s important to note, it appears that an effective dose is strain-specific. In other words, each strain may need to be present in differing amounts than other strains to be effective – there may not be one helpful CFU dosage for all probiotics.
FACT: CFU (colony forming unit) is a measurement of how many probiotics will likely form a colony.
Like most things in the world of microbes, it’s complicated. Multi-strain products can have many different strains in them and a higher CFU than single-strain, which play a factor in the difficulty in determining a definite answer. A recent systematic review found that multi-strain mixtures were not significantly more effective than single-strain probiotics. The most important factor to value in choosing a probiotic supplement is whether the probiotic strain (or strains) have been shown in clinical research to provide a benefit.
Each probiotic is identified by its family name (Lactobacillus, Bifidobacteria, Saccharomyces), species (acidophilus, longum, boulardii), and its strain (HA-11, GG, etc). It is important to recognize, that like the human beings they inhabit, each probiotic strain is unique. Thus, when looking for a probiotic that elicits the desired health benefit, pay attention to its strain. Strains have specific health benefits.
FACT: Probiotic strains are different and can offer unique health benefits.
Here are the 3 top probiotic species based on being the most commonly known, talked about, and used in supplements (in some countries). Each is a link to a helpful article/resource where you can discover more about them:
Prebiotics are typically non-digestible fiber compounds that assist specific members of the gut microbiota, helping them grow within the gut environment. In other words, prebiotics are fibers that probiotics love to use as fuel to help them flourish.
Yes, as a result of fermentation, fermented foods can contain live micro-organisms that are known probiotics. However, not all micro-organisms used in fermentation are considered by the scientific community as probiotics and may not be present in adequate amounts to elicit a health benefit.
Looking for more information about probiotics? Here are some great resources, from peer-reviewed scientific journals:
Choosing an appropriate probiotic product for your patient: An evidence-based practical guide. PLOS One 2018 Dec 26;13(12):e0209205.
A review of dose-responses of probiotics in human studies. Benef Microbes 2017 Apr 26;8(2):143-151.
Efficacy of single-strain probiotics versus multi-strain mixtures: systematic review of strain and specificity. Dig Dis Sci 2021 Mar;66(3):694-704.
Effectiveness of multi-strain versus single-strain probiotics: current status and recommendations for the future. J Clin Gastroenterol 2018 Nov/Dec.
Impacts of gut bacteria on human health and disease. Int J Mol Sci 2015 Apr;16(4):7493-7519.
Gut microbiota in obesity and undernutrition. Adv Nutr 2016 Nov 15;7(6):1080-1089.
Long-term effects of anti-microbial drugs on the composition of human gut microbiota. Gut Microbes 2020 Nov 9;12(1):1795492.
Does probiotic consumption reduce antibiotic utilization for common acute infections? A systematic review and meta-analysis. Eur J Public Health 2019 Jun 1;29(3):494-499.
Role of probiotics in stimulating the immune system in viral respiratory tract infections: a narrative review. Nutrients 2020 Oct;12(10):3163.
Contributed by Allison Tannis
Known for her deliciously geeky words, Allison’s articles and books are read around the world by those curious about where to find the most delicious (and nutritious) places to stick their forks. More at allisontannis.com. Follow @deliciouslygeeky.