Probiotics
Live bacteria that support gut microbiome diversity, immune function, and hormone metabolism.
What is Probiotics?
Probiotics are live microorganisms that, when administered in adequate amounts, confer a health benefit on the host. The most common strains in supplements are Lactobacillus and Bifidobacterium species. Gut bacteria play a role in the metabolism of oestrogen, synthesis of short-chain fatty acids, and modulation of the immune system. The gut microbiome also influences testosterone production via the gut-gonadal axis.
What does the evidence say?
A 2014 study published in Cell found Lactobacillus reuteri supplementation in mice increased testosterone and testicular size, a finding that has generated significant interest but has not yet been replicated in human trials at the same scale. Multiple randomised controlled trials support probiotics for IBS, antibiotic-associated diarrhoea (Hempel et al., 2012 Cochrane review), and immune function. The testosterone-gut connection in humans is an active area of research.
Good evidence from several studies, but with some limitations in size, duration, or methodology.
Dosage guide
| Effective dose | 5–50 billion CFU per day (colony forming units) |
| Maximum dose | No established upper limit for healthy adults |
| Timing | With or before meals: food buffers stomach acid and improves live bacteria delivery. |
Best form to buy
Multi-strain products containing at least Lactobacillus acidophilus and Bifidobacterium lactis. Look for guaranteed viable count at time of use (not manufacture). Refrigerated products often have better viability.
Who benefits most
Anyone who has taken antibiotics recently, men with IBS or digestive discomfort, and those interested in general immune and gut health maintenance.
Side effects and safety
Initial bloating and gas during the first week as gut flora adjusts. Rare: serious infections in immunocompromised individuals (not relevant for healthy adults).
“The evidence for gut health is strong. The testosterone link is fascinating but not yet proven in humans at meaningful scale. Take it for gut and immune reasons, not primarily for testosterone, and you won't be disappointed.”