Probiotic yogurt: fact vs fiction

Probiotic yogurt: fact vs fiction

You know that yogurt commercial with piles of women happily munching on yogurt in a sunny field laughing about nothing? What the heck, yogurt marketers? Who are these women?? I mean….technically I’m one of them. I eat yogurt every other day. But instead of in a field, I usually shovel it in my mouth standing over the sink. Classy, I know.

Besides being delicious and easy and an awesome vehicle for sugary granola, there’s the mysterious promise of “health benefits” from the probiotic bacteria. As a microbiologist, I’ve been skeptical of these health benefits:

1) I couldn’t imagine the bacteria surviving the acidic gastric juices

2) If they DID survive, I couldn’t imagine they could push aside the normal flora and establish residency

After years of skeptical yogurt-consumption, I realized that I’m a scientist and research is my JOB. Somebody probably answered these questions already! I hit the metaphorical books (aka the internet) and discovered that I was RIGHT but also mostly wrong.

First of all, mysterious health benefits of consumed bacteria have been a subject of investigation for over one hundred years. An amazing review cited a 1906 article where a scientist isolated Bifidobacterium from baby poop and insisted it could displace pathogenic gastrointestinal bacteria. Warning: not only is this article in French, it’s not actually accessible via internet as far as I can tell.

Anyway, my first concern is decidedly wrong. Many bacteria, especially of the genera Lactobacillus and Bifidobacterium, have strong acid tolerance responses determined through in vitro methods or simple recovery from fecal samples after oral administration. In retrospect, my first concern is rather silly because obviously certain bacteria survive the harsh environment of the stomach to colonize the intestines in the first place!

My second concern, however, contains hints of truth. The aforementioned review suggests in the 1930s, scientists discovered that the two bacteria that make yogurt, Lactobacillus bulgaricus and Streptococcus thermophiles, were unable to colonize the gut (I knew it). So, Lactobacillus acidophilus was added to the yogurt, a bacterium that can persist longer in the the gut. L. acidophilus is still a major constituent of modern yogurt. A quick exploration of pubmed, however, shows that the original yogurt bacteria, using current molecular methods of detection, are sometimes detectable in the stool….sometimes. Not always. Especially, wimpy old Streptococcus, which almost never survives. AGAIN, this bring us back to my original concern! Are the bacteria just surviving in the intestines? Or are the benefits of probiotics actually through colonization? Or do the bacteria magically sprinkle “health benefits” as they pass by the normal flora on their way to the septic system?

I would argue there is a definitive difference between the ability of bacteria to survive, attach and colonize the GI tract. While some probiotics are capable of host attachment and indeed, Lactobacilli make up < 1% of resident bacteria in human intestines, it seems rare for an orally-administered probiotic to persist in the gut through colonization. This suggests the benefits of probiotics only occur if consumption is maintained. The minimal serving of daily yogurt I’ve seen for these randomized trials with positive correlations to mysterious health benefits was ONE CUP. Goodbye variety and interesting breakfast meals, I have to eat gallons of yogurt a month.1

Fortunately, probiotics also come in pill form, which avoids the issue of funneling yogurt on a daily basis. And while my second concern contains hints of truth, exploration into the subject has convinced me that probiotics have many mechanisms for improving health without colonization. Probiotics can metabolically support flora, influence the immune system and antagonize pathogens all without establishing permanent residency.

Am I going to run out to my local health foods store and stock up on probiotic pills? No! Will I continue to eat yogurt? Yes! A survey of college students in Japan showed a dose-dependent effect on the microbiota based on number of yogurts eaten per week. In other words, as little as 1-2 yogurts a week had a significant increase of beneficial bacteria within the normal flora and the effect was amplified with more yogurts. Good enough evidence for me.

Thanks to my mom for the OJ and peach schnapps (aka Fuzzy Navel). Enjoy happy hour y’all!

1Speaking of gross amounts of yogurt, Activia was actually sued by the FTC for misleading advertisement in 2010. Activia claimed “clinically-proven” regulation of digestion occurred with a single serving a day because of the probiotic Bifidobacterium regularis. Firstly, the placebo data was withheld from publication because there wasn’t a statistically-significant difference with the Activia group. Secondly, slowing on intestinal transit only occurring upon eating three Activia yogurts a day. Scandal!!

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