Do probiotics survive stomach acid?
Some do, and the label rarely tells you which. The strain code is the number that matters, and most tubs do not print one. Here is what to look for.
Short answer: some survive, most of the dose does not, and the bigger problem is that you usually cannot tell which strain you bought. A label reading Lactobacillus acidophilus names a species, not an organism anyone studied. The research is done on specific strains, written like LGG or DSM 17938, and a tub without one of those codes cannot be checked against anything.
Stomach acid is the objection everyone raises, and it is real. It is also not the reason most probiotic supplements are hard to evaluate.
The acid part
Stomach pH sits somewhere around 1.5 to 3.5, which kills the large majority of ingested bacteria. Some strains tolerate it much better than others, and manufacturers deal with the rest in two ways.
Delayed-release or enteric-coated capsules pass through the stomach intact and open further down. Higher counts are the cruder answer: send in far more than needs to arrive.
Both work to a degree. Neither is printed on the front of most tubs.
The number that is printed, and what it leaves out
CFU means colony forming units, and it is the count on the front. Two things about it are worth knowing.
First, most labels state CFU at time of manufacture. Live bacteria die off across a shelf life, so the count on the day you swallow it is lower, sometimes by a lot. A label that says "at expiry" or "through end of shelf life" is making a meaningfully stronger claim than one that does not, and it costs the manufacturer more to guarantee.
Second, CFU is a quantity with no quality attached. Fifty billion of a strain nobody has studied is not better than one billion of one that has been.
Strain codes are the real tell
This is the part worth taking away.
Probiotic effects are strain specific, not species specific. Two organisms can share a genus and species and behave completely differently. So research names strains precisely:
- Lacticaseibacillus rhamnosus GG
- Limosilactobacillus reuteri DSM 17938
- Bifidobacterium longum BB536
Those trailing codes are the organism. A label listing "Lactobacillus acidophilus" with no code has told you roughly as much as a supplement listing "amino acids".
If there is no strain code, there is no way to look up whether anything was ever demonstrated for what is in the tub.
What the good labels do
They print the full name and code for every organism, give the CFU per strain rather than one combined total, and state the count at end of shelf life. Some also name the delivery method.
That is four pieces of information, all of which fit on a label, and most products give you one of them.
What to do
- Look for strain codes. Letters and numbers after the species name. No code, no way to check.
- Check whether CFU is at manufacture or at expiry. Only one of those is the dose you actually take.
- Ignore the size of the CFU number by itself. It is the easiest figure to inflate and the least informative one on the tub.
Related reading: can you take too many supplements and do greens powders replace vegetables.
Verdict reads the label, not the reputation. Photograph the supplement facts panel and it pulls every dose, compares each against the amounts used in published research, and adds up your whole stack. It reports the arithmetic. It does not tell you what to take.
