A few years ago, researchers noticed something odd. They'd been studying the effects of yogurt on obesity when they realized that some of the mice they'd been using were walking funny.
When they turned the wee little beasties over, they discovered that they'd grown bigger balls, so much so that they walked with a "swagger," kind of like John Wayne or maybe an NBA player who'd just drained a 3-pointer from 30 feet out with a second left on the clock.
Two groups of mice had been involved. One had been fed a junk-food diet plus yogurt and one had been fed a healthy-diet plus yogurt. The junk food eaters had experienced a 15% increase in testicular size while the healthy eaters had only experienced a 5% increase. (The junk food eaters had smaller balls to begin with, hence the disparity in percentages.)
I bet you that normal, non yogurt-eating mice began sneaking furtive looks at the big-balled mice while in the locker room – not because they were necessarily gay or anything, but because they were intrigued and maybe a little jealous.
Anyhow, the healthy-diet plus yogurt eaters also inseminated female mice faster and produced more offspring, but the beneficial side effects of the yogurt weren't restricted to their mousey testicles.
The mice also grew shinier coats that had 10 times the "follicular density" of normal, non-yogurt eating mice, giving them hair/fur quality on par with the members of a mousey K-pop band.
The results led to a question: Would the favorable side effects of eating yogurt transfer to humans? It seems they might. Harvard nutritional epidemiologist Jorge Chavarro, who's made a nice career studying all things testicle related, has found that ingesting yogurt and other low-fat dairy foods improves the semen quality in human males.
Researchers seem to think that a particular strain of bacterium in the yogurt was responsible for the big-balled rodents and superior-semen shooting men. That strain of bacteria is known as Lactobacillus reuteri.
John Wayne vs. Sparkly Ponies
Here's the weird thing. You know how people are always saying that men today aren't what they used to be, how they're less "manly"? Well, oddly enough, it might correlate with levels of L. reuteri.
Back in the 1960s, 30 to 40 percent of the population carried around at least some L. reuteri in their guts. Today that number is estimated to be between 10 and 20 percent.
John Wayne? No doubt full of L. reuteri. Guy who collects My Little Pony figurines? Probably not so much.
What the bacterium supposedly does is maintain or increase the number of Leydig cells in the testes and Leydig cells are responsible for producing testosterone. As a result of more Leydig cells or healthier Leydig cells, the testicles get a little heftier and produce more testosterone.
But beyond bigger and better balls, L. reuteri has some other interesting effects, too. The bacterium appears to decrease the production of IL-17, a cytokine intimately involved with inflammation, obesity, and various autoimmune diseases.
What did the L. reuteri-filled yogurt have to do with the lushness of mouse fur? The researchers weren't sure. Regardless, there's one big problem – American yogurts typically contain only 2 to 7 strains of bacteria and L. reuteri isn't usually one of them. That in itself might explain the discrepancy between population levels of the bacteria in the 1960s and today.
Not to worry, though. You can often find L. reuteri in American-made kefirs.
What's a Kefir?
Kefir's a milk product made from starter grains of bacteria and yeast. The end product is a slightly sour, slightly fermented beverage that even most lactose intolerant people can drink.
While it's traditionally made from cow, goat, or sheep milk, you can make it from any type of plant-based milk (soy, rice). It can even be made from coconut milk or coconut water to make coconut kefir.
Aside from containing more bacterial species, some studies have shown that the bacteria in kefir seem to be more "faithful" than those found in yogurt. In other words, the bacteria in the kefir attach to the lining of the gut and form colonies instead of dying off or being excreted.
Kefir, like most anything else nowadays, comes in a variety of fruit flavors sweetened with a metric f-ton of cane sugar, but drinking anything else but the plain, unsweetened stuff isn't congruent with the big balls you'll presumably grow from drinking it. Just make sure L. reuteri is listed on the side panel.
You can also buy L. reuteri capsules but I'm personally not entirely sure they "seed" as well as they do when you get them straight from kefir.
How to Best Use Kefir
I drink one 8-ounce glass of kefir a day, either divided into two servings or all at once. I sometimes drink it by itself, plain, or I add a scoop or two of Metabolic Drive® Protein to it (for flavoring and the protein, of course) and sort of half-spoon it, half-drink it.
Alternately, I pour a few ounces on my breakfast cereal and then make up the extra with oat milk, cashew milk, or cow's milk.
The secret seems to be eating it on a regular basis, making it as much a part of your day as the coffee you drink in the morning. Your balls might not get visibly bigger, but there's a decent chance your testicular health, and maybe your hair, will improve.
- Chavarro, Jorge, et al. Dairy Intake and semen quality among men attending a fertility clinic," Fertility and Sterility, Volume 101, Issue 5, May 2014, Pages 1280-1287.
- Dolgin, Elie, "Mice That Eat Yogurt Have Larger Testicles," Scientific American, Friday, May 4, 2012.
- Poutahidis, Theofilos, et al. "Probiotic Microbes Sustain Youthful Serum Testosterone Levels and Testicular Size in Aging Mice," PLOS One, January 2, 2014.
- Rosa DD, Dias MMS, Grześkowiak ŁM, Reis SA, Conceição LL, Peluzio MDCG. "Milk kefir: nutritional, microbiological and health benefits," 2017 Jun;30(1):82-96.
- Sharifi M, et al. "Kefir: a powerful probiotics with anticancer properties," Med Oncol. 2017 Sep 27;34(11):183.
- Vinderola CG, et al. "Immunomodulating capacity of kefir," 2005 May;72(2):195-202.
As an Amazon Associate, T Nation earns from qualifying purchases. When you buy something, using the retail links in our articles, we may earn a small commission. T Nation does not accept money for editorial reviews. Read more about our policy.