Why do commercial probiotics often fail to colonize the human gut? Contrary to what you may hear, it's not a matter of concentration.
Non-native strains
Many probiotic strains are not native to the human gut and therefore haven't evolved the specific genetic traits that allow them to survive and thrive in the gut environment. These traits include:
Mucosal adherence: The ability to stick to the gut epithelial lining.
Acid resistance: Surviving the harsh, acidic environment of the stomach.
Without these adaptations, non-native probiotic strains struggle to establish themselves and colonize effectively.
Niche availability and competition
The gut microbiome is a complex ecosystem with limited space and resources. For a probiotic strain to colonize, it needs to find an available niche. This can be challenging because:
Existing bacteria may already occupy suitable niches.
Microbes face intense competition for resources.
One study found that a specific strain of Bifidobacterium longum had more success colonizing in individuals who didn't already have native B. longum strains. This suggests that when a niche is already filled by a similar species, it's harder for the probiotic strain to establish itself.
