Why Are Men Taking This Probiotic to Increase Testicle Size?

Lactobacillus reuteri is a probiotic designed to help the digestive system. But lately, the bacterium is being touted on social media — sans evidence, unsurprisingly — as a way to increase testicle size.

Per Wired, any scientific evidence that L reuteri does “anything to expand testicles is almost nonexistent,” but that hasn’t stopped several individuals and at least one company from touting this purported … I don’t know, benefit? A lot of the current claims reportedly base their ball-enhancement theory on a single 2014 study.

“Our previous studies and observations, taken together, led us to hypothesize that dietary L. reuteri may act to prevent age- and obesity-related testicular atrophy in mice,” those researchers noted. “The results of the present study confirmed this hypothesis. The testes of probiotic-fed aged mice were rescued from both seminiferous tubule atrophy and interstitial Leydig cell area reduction typical of the normal aging process. Preservation of testicular architecture despite advanced age or high-fat diet coincided with remarkably high levels of circulating testosterone.”

The Colorado-based supplement supplier UMZU seems to be the most egregious offender of big ball claims; they suggest their Floracil50 probiotic “contains the only living bacteria that can solve the problem of small balls.” That company’s founder, Christopher Walker, is an influencer with 423,000 Instagram followers. UMZU’s website suggests Walker healed a brain tumor naturally through “diet, training, lifestyle and supplementation.”

While some users of UMZU products (and knockoffs) claim they’ve seen results, others have claimed they just got bad gas. The need for some men to seek larger testicles appears to be connected with societal ideas around testosterone and masculinity, but the article suggests this particular probiotic use has also seen increased interest amongst bodybuilders who may have shrunken testicles due to steroid use.

Scientists are not impressed with UMZU’s claims. “I mean, on the level of weak evidence for something, this is as weak as it can possibly get,” Faysal Yafi, medical director of the department of urology’s Men’s Health program at UC Irvine in California, told Wired. “To call it a stretch is the least you could say, basically. It’s really not rooted in any kind of evidence whatsoever.”