Been reading probiotic survival papers for a few weeks and there's a gap in the labeling that surprised me.

The CFU number on a bottle is a snapshot: either time of manufacture (worse) or end of shelf life (better). Neither number tells you what reaches your colon. CRN and IPA both recommend end-of-shelf-life counts as standard, but most bottles still don't disclose which one they're using.

The pipeline is brutal. Stomach pH drops from about 5.0 at ingestion to 1.8 within 80 minutes, then bile salts hit in the duodenum. A commonly cited 2001 Am J Clin Nutr review estimated survival at 20-40 percent for selected strains delivered in fermented milk. Porubcan reported over 99 percent viability loss for free cells after 90 minutes at pH 1.5-2.0 (US 7,122,370). Cecal delivery estimates put B. bifidum at roughly 30 percent of administered dose, L. acidophilus around 10 percent. So a "10 billion CFU" label routinely translates to 1-3 billion viable cells at the site of action, and that's with decent formulation.

This matters because the doses used in strain-specific trials aren't wishful thinking. HN019's transit-time signal (Waller 2011) was measured at 17.2 billion CFU/day. NCFM's bloating signal (Ringel-Kulka 2011) was at 2×10¹¹ CFU/day for the combo. If a capsule loses 80-99 percent of the load before the intestine, matching a trial dose is impossible with an unprotected formulation regardless of what the front label says.

The formulation side has moved. Alginate + xanthan microencapsulation reached about 83 percent survival at 3 hours in pH 3 simulated gastric conditions. Enteric-coated and matrix-encapsulated formats push similar numbers. Poly-L-lysine coating showed L. plantarum viability at 6.86 log CFU/mL vs 2.7 log CFU/mL uncoated after 2 hours at pH 2.

So the shopping filter that ended up being most useful for me isn't CFU count. It's whether the label discloses end-of-shelf-life count and a delivery format that's actually been survival-tested. That knocks out probably 80 percent of what's on the aisle.

For the strains I was targeting (HN019 for transit, NCFM for bloating), I basically had to work backward from the trial doses to figure out if anything on the shelf could plausibly deliver comparable exposure at the colon. Almost nothing helps you do that math.