I previously reported that a manual count (via progressive dilutions of the sample) of our L. reuteri yogurt yielded a bacterial count of 28 billion per 1/2-cup serving—substantial, far more than bacterial counts (of Lactobacillus bulgaricus and Streptococcus thermophilus) contained in conventional yogurt that are typically in the millions. In the world of microbiome manipulation, it is becoming clear that millions make no difference; tens or hundreds of billions are required for meaningful biological effect when introduced into the 100 trillion microbes of the human microbiome. The trivial bacterial counts of conventional store-bought yogurt are due to the push to minimize production times: 4 hours of fermentation is more financially productive than our 36 hours of fermentation. But we don’t care about financial productivity; we care about biological and health effects.

I therefore had three successive samples of our L. reuteri yogurt analyzed by another method: flow cytometry. This is a computerized system in which bacteria are counted using a laser as bacteria flow through a thin column in liquid. By this more precise method, the counts were much higher: 204 billion per 1/2-cup serving.

That’s impressive. It means that my method of using prolonged fermentation to allow 12 doublings (L. reuteri doubles every 3 hours at 100 degrees F) in the presence of prebiotic fiber works—and it works extravagantly. This is a big part of the reason why most people consuming the L. reuteri yogurt are experiencing huge health benefits rapidly. Recall that we start with the relatively trivial bacterial numbers of the two L. reuteri strains contained in the BioGaia Gastrus product of 200 million per tablet, a dose conceived for benefits to infants to reduce regurgitation and infantile colic. Take a tablet and not a lot happens for us adults. But make “yogurt” using prolonged fermentation and prebiotic fibers and you increase bacterial counts 1000-fold.

I believe this means that we have leeway in making mixed-culture yogurts, i.e., fermenting with more than one species. Fermenting bacteria is a lot like growing vegetables in your backyard garden. In your 10 x 10-foot plot, say you plant tomatoes. At the end of the growing season, you are going to have a bounty of tomatoes. But plant tomatoes, zucchini, cucumbers, and squash—how many tomatoes will you have? Far fewer. The more vegetables you plant, the more they compete for space, water, sun, and nutrients. The same process applies to microbes: Ferment with one species and you will obtain a high count. Ferment with more than one species and counts will be lower.

One thing I do not know is the number of bacteria required to generate the effects we desire, such as smoother skin with reduced wrinkles, accelerated healing, restoration of youthful muscle and strength, and increased empathy, as we have not yet performed a dose-response study. Do these effects develop at 10 billion, 25 billion, 50 billion, 100 billion? Is the effect greater with higher counts? These questions have yet to be explored.

But I believe you are on solid ground if you ferment L. reuteri with one or two additional species such as Lactobacillus casei Shirota for enhanced immunity and deeper sleep, Lactobacillus gasseri BNR17 to shrink your waist and push back bacterial overgrowth, or Bacillus coagulans GBI-30,6086 for reduced joint pain and reduced muscle breakdown during strenuous exercise.