Survival through the gut is considered a key characteristic of probiotic strains as the mechanism of activity is associated with the transient presence, growth and activity of the live probiotic cells in the gut. The strongest evidence for survival is detection of the strain in the faeces of people after they have consumed the probiotic.    

Lactobacillus casei Shirota, the strain in Yakult, was selected and cultivated because of its ability to survive the harsh conditions of the gut. There are several peer-reviewed publications that describe human studies showing the survival of L. casei Shirota including, but not limited to, studies in European¹ and Asian populations², children³ and critically ill children⁴.

In vitro or model studies are not proof of gut survival in vivo, however they do provide useful information on factors that can affect the viability of the strain. When L. casei Shirota was exposed to physiological levels of gastric, bile, and pancreatic juices, for a realistic time of digestion, it was confirmed to have an excellent survivability, particularly when embedded in a milk matrix.⁵

Probiotic bacteria consumed are generally only transient in the intestinal tract and cannot establish permanent residency in the gut of the host. Within weeks of ceasing probiotic intake, generally the strains consumed are no longer detected in the faeces. However, studies suggest that complementary probiotic intake may help our resident microbes by encouraging the growth and numbers of our own bacteria; see our page of MODULATION to find out how Lactobacillus casei Shirota modulates the gut microbiota.

Survival of Lactobacillus casei Shirota through the gut

Tuohy et al. (2007) Journal of Applied Microbiology 102(4):1026-1032.

Method 

This double-blind, placebo-controlled study at the University of Reading, involved 20 healthy volunteers who consumed either L. casei Shirota (at least 13x10⁹ CFU) as a fermented milk drink or placebo for 21 days. Stool samples were collected at days 0, 7, 14, 21 and 28 to measure survival of L. casei Shirota and changes to faecal bacteria.   

Results 

Seven days after subjects started to take the probiotic, L. casei Shirota was recovered at a mean level of 1.1 x 10⁷ CFU/g of faeces, and this level was maintained throughout the course of probiotic consumption and decreased after participants stopped consuming the probiotic.

Concurrently, in subjects consuming L. casei Shirota, an increase in total lactobacilli was observed, which persisted even after probiotic consumption had stopped. Bifidobacteria were also found to increase during the 21 days, but this increase was not sustained once consumption of L. casei Shirota had stopped.

1. Tuohy et al. (2007) Journal of Applied Microbiology 102(4):1026-1032.

2. Mai et al. (2017) Asia Pacific Journal of Clinical Nutrition 26(1):72-77.

3. Wang et al. (2015) Annals of Nutrition & Metabolism 67:257-266.

4. Srinivasan et al. (2006) Journal Pediatric Gastroenterology and Nutrition 42:171-173.

5. Lo Curto et al. (2011)  Food Microbiology 28:1359-1366.