Soured milk bacteria surviving the trip through the human gut
What it found
Up to 51.2% of a specific bacterium from soured milk survived the trip through the small intestine in people.
About 28.4% reached the stool alive.
What they found
Studies in people
Survival in small intestine
In four people, up to 51.2% of the tracked bacteria were still alive in the lower small intestine during the first two hours. This was higher than survival rates reported for other similar bacteria in past studies.
Survival in stool
After daily consumption, about 28.4% of the tracked bacteria appeared alive in stool samples from six people. Bacteria levels stayed steady from day 4 to day 7, then dropped quickly when people stopped drinking the soured milk.
High numbers in gut
At its peak, the tracked bacteria outnumbered the usual gut bacteria by 10 to 100 times in the small intestine. In stool, it made up about 0.1% of the total gut bacteria.
Other findings
Why survival differed
The authors suggest the bacteria might multiply in the large bowel or stick briefly to the gut lining. They also note that secretions like bile might have affected the small intestine measurements.
What the authors conclude
- They conclude that this bacterium survives well as it travels through the human digestive tract.
- They say the high number of bacteria reaching the small intestine might be enough to produce a beneficial effect.
- They note that more work is needed to find out if the bacteria are active and what they do inside the human gut.
How it was done
Earlier work showed this bacterium could shorten bouts of diarrhea in young children and change gut bacteria in babies. The authors wanted to know how many of these bacteria actually stay alive as they travel through the human gut.
Ten healthy adults drank soured milk containing a tracked strain of Lactobacillus casei for up to 8 days. Seven volunteers had a tube placed in their small intestine to collect fluid after one dose. All ten gave stool samples over several days to count surviving bacteria.
What it can’t tell you
- This trial only tracked whether the bacteria stayed alive, so it cannot show if they improved digestion or health.
- Only four to six people provided usable data for each part of the study, so results might vary in a larger group.
The paper
- Title
- Survival of Lactobacillus casei in the human digestive tract after consumption of fermented milk
- Type
- Clinical trial
- Evidence
- Studies in people
- Summarised from
- Full text
- Cite
- Oozeer R, Leplingard A, Mater DD, et al (2006). Survival of Lactobacillus casei in the human digestive tract after consumption of fermented milk. Applied and environmental microbiology. doi:10.1128/AEM.00722-06Free full textPubMed 16885316DOI
Summary written 30 Sep 2026. Check it against the paper before it changes what you eat. How we summarise papers · Report an error