Probing the World of Probiotics: Interview with an Expert

Interview by: Dr. Julie Ennis, PHD, OICC Research Fellow.

With a growing understanding of just how large, diverse and important the populations of bacteria living within the human body are, research into how we can alter the microbiome and what potential health benefits this may have is exploding. 

The potential for diet to impact the balance of gut bacteria and improve health is an area of particular interest. More and more probiotic foods and dietary supplements are being marketed for this reason.

Can these products live up to the marketing hype? In today’s blog we interview Dr. Mary Scourboutakos, PhD, who was the lead author on a paper published this year that looked at the status of probiotic-containing foods in the Canadian food supply and clinical trial research.(1) We’ve brought some of the most common questions our Naturopathic Doctors get from patients about probiotics from the diet.

To start us off, what are “probiotics” and why do they matter?

To put it simply, probiotics are “good bacteria” that survive digestion and live inside of us. While residing in our guts (aka intestines), they work for us by aiding digestion, supporting the walls of the intestine and interacting with our immune cells. In fact, we couldn’t survive without them! Most people don’t realize that we all have two to six pounds of bacteria inside of us. And the more good “probiotic” bacteria we have, the harder it is for bad bacteria to move in, multiply and make us sick.

What foods are probiotics found in?

In our study, probiotics were primarily found in yogurt and fermented milk drinks (called kefir). Most people mistakenly think they’re getting probiotics from all yogurt, but it’s important to realize that while all yogurt is made with bacteria, not all bacteria are probiotic! Therefore, unless the label says “probiotic” there’s no guarantee that a food will provide good bacteria.

Beyond yogurt and fermented milk, there are additional foods entering the marketplace such as teas and juices that can also provide probiotics.

Fermented foods—like pickles, sauerkraut and kimchi—could potentially be a source of probiotics. However, if you buy fermented foods at the grocer y store you probably won’t get any probiotics for two reasons. 1) These foods are often heat-treated and high temperatures can kill bacteria; and 2) these products have very long shelf-lives that could exceed the lifespan of these good bacteria.

If you make fermented foods yourself they could provide probiotics. However, unless you have the lab skills to analyze the strains of bacteria in your food, there’s no guarantee whether or not the strains in your food are indeed probiotic.

What are the key findings from your research on probiotics?

We found that different probiotic food products contained different types of probiotic bacteria. This finding led us to conduct a systematic review of all the published literature that tested these bacteria in humans. After conducting the review, we found that different types of probiotic bacteria are associated with different health benefits. This means that not all probiotic food products are created equal.

While one product might help with constipation, another could decrease your risk for the common cold. The catch is, the consumer doesn’t know which product can offer which benefit. That’s where our study came in. Our goal was to synthesize this information and figure out what benefits consumers can actually get if they eat these products. We created a chart that summarizes our findings.

The second, more unexpected, finding from our study, was that the dosage of probiotics that was tested in clinical trials was often higher than the dosages found in products on grocery store shelves. The studies were reviewed tested anywhere from two to twenty-five times the dosages commonly found in the food products!

This means that even though these food products contain good bacteria that have been proven to have certain health benefits, they often don’t contain the dosage that has been proven to offer the health benefit. We hope that in the future, with improved probiotic labelling laws companies will have more incentive to put higher doses in their products. Currently, most products are simply putting the minimum that’s required in order to be labelled “probiotic”.

Does the amount of bacteria found in a food product decrease over time? How quickly should someone finish their yogurt or kefir once they’ve opened it to make sure that they are getting the most bacteria?

The sooner you eat probiotic yogurt or kefir, the better. Bacteria are constantly dying. Therefore, the dosage in most probiotic food products is irreversibly declining. This is one food you should never eat past the expiration date, because by then, the probiotic benefit will likely be gone.

Does sugar affect the amount or type of bacteria present in foods? When it comes to bacteria, would “plain” yogurt be better than flavoured?

Plain yogurt is usually the best choice. That being said, some of the bacterial strains with the most evidence behind them, came in products that contained 10 grams of sugar per serving. But keep in mind, that’s still only one-quarter of the sugar found in a can of coke!

Sugar doesn’t affect the bacteria present in your food, but it can affect the bacteria already in your gut. That because when you eat, you’re not only feeding yourself; you’re also feeding all of the bacteria that live inside of you. Foods high in certain types of fiber (found in asparagus, Jerusalem artichoke, bananas, garlic, leeks, onions, tomatoes, barley, rye, and dandelion greens) tend to selectively feed good bacteria. Unfortunately, a diet high in sugar can preferentially feed bad bacteria and consequently promote their growth. Hence, it’s always a good idea to consume sugar prudently.

What about kimchi or kombucha? Are there non-dairy sources of probiotics that are as good as dairy products?

These products could potentially offer probiotic health benefits. However, without knowing the bacterial strain and dosage they contain, there’s no guarantee. Always look at the label!

It’s not the food itself that determines whether or not the product is a good source of probiotics. Instead, the specific type and dose of bacteria present is what distinguishes one probiotic food source from another.

Are the effects of probiotics long lasting? How often do probiotics need to be consumed to see changes in the microbiome?

Probiotic bacteria have a short lifespan and are constantly passing through us. Therefore, it’s important to consume probiotics consistently. In most of the studies that we reviewed, these products were consumed daily. Studies suggest that if you stop eating probiotics, your gut will revert back to its original state. That being said, beyond eating probiotics the other thing you can do is eat prebiotics. Prebiotics are food for probiotics. They’re found in the aforementioned foods including asparagus, Jerusalem artichoke, bananas, garlic, leeks, onions, tomatoes, barley, rye, and dandelion greens.

We are grateful to Dr. Scourboutakos for taking the time to answer some of our questions about probiotics in foods.

Dr. Mary Scourboutakos, PhD

Dr. Mary Scourboutakos is a nutrition expert with a PhD from the University of Toronto. Mary is a former Vanier Scholar whose research has been published in prestigious medical journals and has helped influence public policy at City Hall and Queen’s Park. In addition, Mary is an avid science communicator who is devoted to spreading the word about the importance of eating-well as a means to live optimally. She has appeared on CBC (TV & radio), CTV & TVO and she blogs at