A Scientific Look at the Benefits of Probiotics

I’m concentrating on probiotics and fermenting for the month, and this is the first installment, here is an index I’ll add posts to as I publish them. I wanted to write an epic thorough post on probiotics, complete with scientific references and explanations. The problem is, that’s called a book. For now, please accept this truncated and incomplete version. I’ve tried to include ample sources to demonstrate that the immense importance of probiotics is not some hippy-feel-good theory, but grounded in science.

A Scientific Look at the Benefits of Probiotics

I’ve long known that ‘probiotics’ were good for you in a general way, hearing advice to take them after antibiotics. We are, however, discovering functions of probiotics that are actually fundamental to our well being, as opposed to being a nice thing to have. Studies and experiments are continually discovering new ways that these little bugs benefit the human host and I think we are just starting to uncover the tip of the iceberg.

Probiotics are mostly bacteria, with a few kinds of yeast, that populate our bodies. We tend to concentrate on the ones that reside in the gut, but beneficial bacteria are also present on all the places of contact with the ‘outside’ world, including skin, eyes, genitals, and breastmilk. For our purposes, we will focus on beneficial flora in the gut.

Technically, probiotics are defined as “live micro-organisms which, when administered in adequate amounts, confer a health benefit on the host” by the World Health Organization. This definition is mostly in reference to supplements and advertising claims, so that ‘probiotic’ on a label must have scientific evidence of some health benefit from the strain of bacteria or yeast that is being promoted. With an estimated 1000 species of beneficial flora residing in or on the human person and however, there is much more research before all the health benefits that do exist are found out. And of those 1,000 species of beneficial bacteria in the human ‘eco-system’, each of those species has multiple strains, each of which can have a different influence on the human host.

As an example of how much we don’t yet know, the second most common bacterial species listed in the American Gut Project ( a project examining swabs/samples from a variety of people mostly in the United States) doesn’t have a name – in fact, it doesn’t even have a named genus. And the most common bacteria mapped by the American Gut Project is practically non-existent in the Hanza tribe of Tanzania, a group still living a hunter-gatherer lifestyle. This study, as well as other, indicates that the composition of an individual’s microbes is dependent on that individual’s diet.

One way of categorizing probiotics is if they are resident or transient. Some probiotics are permanent, colonizing in the gastrointestinal tract and staying. Transient flora, on the other hand, are usually eaten and eliminated, although some colonize temporarily in the gut. Even though they are temporary, the bacteria still perform valuable functions and may even enhance the performance of the resident flora. The fact that beneficial flora are transient points to the importance of consuming probiotics on a continual basis.

Benefits of Probiotics (heavily relied on this article)

Although using the generic term of probiotics when listing the benefits, each benefit is influenced by a different strain, never mind species, of beneficial flora. There is evidence that there is some overlap, or that some types of probiotics can change their function based on need, but taking a general probiotic supplement or eating only one probiotic food (like yogurt) will not have the effect of conferring all the listed benefits of probiotics.


Some of the more obvious benefits of probiotics are related to the gastrointestinal tract, given that that is where they reside. Probiotics release enzymes, which help break down food and make it more available for the body to absorb and use.

Probiotics also have an effect on elimination, correcting both diarrhea (from various causes) and constipation. They can heal diarrhea by getting rid of pathogens by releasing specific bacteriocins (something like an antibiotic), creating an inhospitable environment, competing for space, strengthening the immune system, and increasing mucins (a component of mucus) that prevents pathogens from attaching to the intestinal wall. As for constipation, certain probiotics can increase peristaslis activity (the squeezing of the digestive tract to move food along).


Probiotics can synthesize vitamins, most specifically vitamin K (necessary to blood coagulation and utilization of calcium) and some B vitamins, most notably riboflavin, folate, and B12.


Probiotics have an anti-inflammatory effects, both on the gut and in other parts of the body. One study found that one bacteria helped across a range of inflammatory diseases: ulcerative colitis, psoriasis, and chronic fatigue syndrome. Given the breadth and prevelence of chronic inflammatory conditions, including insulin resistance, atherosclerosis, rheumatoid arthritis and neurodegenerative diseases, the idea that a probiotic can reduce inflammation in the body has exciting potential.

Immune System

The gut is actually responsible for about 70-80% of your immune system. That means that your ability to fight off the flu virus, the bacteria from a sneeze, and other harmful pathogens depends on the strength and health of your gut. The health of the immune system also relates to the increasing occurrence of autoimmune diseases.

In the lining of the digestive tract exist a large number of immune cells, which are transported throughout the body via the circulatory and lymphatic systems. Probiotics strengthen the gut wall (the epithelial cells), thereby strengthening the barrier guarding against pathogens penetrating the gut wall.

As well, probiotics increase the acidity of the digestive environment, which kills off many pathogens. They also can influence how some immune cells to suppress inflammation. (More on gut immunology.)

Food Allergies and Eczema

Food allergies rose a whopping 50% between 1997 and 2011. Allergies happen when the body identifies a molecule, such as from peanuts or milk, as harmful to the body and start attacking it. Evidence is building that food allergies and intolerances are probably due to ‘leaky gut’, or when the barrier of the intestinal wall is not strong enough and the offending molecules slip through into the blood stream. Probiotics can help in multiple ways, by releasing enzymes that help break down food, by strengthening the barrier of the gut, and reducing inflammation. As some skin conditions like eczema are a result of internal reactions to particles, probiotics can help with eczema as well.

Urinary Tract Infection

Common knowledge links probiotics with bladder infections, however, only a few specific strains have colonized in the urogenital area in clinical studies, and those specific strains are only available commercially in Austria. All the products that claim to populate the area with probiotics may not be effective. General probiotic health will help UTI’s by improving the immune system and reducing the number of pathogens in the digestive tract (which can infect the urethra via the rectum). Studies have had some success with probiotics and vaginitis as well.

Babies and Birth

It has long been thought that babies are in an germ-free environment in the womb and have their first exposure to bacteria when coming through the birth canal. A recent observation that bacteria are present in meconium, a newborn’s first poo, led to a study of the microorganisms of the placenta. They discovered that the placenta harbours a microbiome most similar to those found in the mouth, and that some of those microbes cross from the placenta to the baby.  Despite this new information, the birth canal and breast milk continue to be important sources of probiotics, although the birth canal could expose the baby to harmful bacteria as well. There is some evidence that the types of resident bacteria do not change after toddlerhood, so this increases the importance of parents’ having healthy microbes (the mother for obvious reasons, the father as he influences the microbes of the mother through contact) and raises the question of inherited health problems, not via genetics but via handed down microbes.


Other studies have been done/are being carried out to determine the effect of probiotics on health problems such as cancer, blood lipid levels, HIV, and oral health. Probiotics can also affect sleep (this blog is fascinating)!

One more area of interest is the microbiome-gut-brain connection, which basically means the relationship between the microorganisms living within the body, the health of our gut, and our mental health. I will, however, leave that to it’s own post.

If you find this article helpful, please leave a note! I know it doesn’t look like much, but researching a topic is very time consuming and brain challenging, and if it doesn’t benefit anyone I’ll just post recipes. 🙂

Have you used probiotics to benefit your health? How did they help?

Shared at Fat Tuesday, Pennywise Platter Thursday, Real Food Wednesday, Allergy Free Wednesday