Survival through the gut is considered a key characteristic of probiotic strains as the mechanism of activity underlying most health benefits is associated with the transient presence, growth and activity of the live probiotic cells in the colon.
A simple way to demonstrate this scientifically is to check for the presence of the live strain in the faeces of volunteers who have ingested the probiotic. This has been done in several trials with Yakult (contact us for reference list).
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 Lactobacillus casei Shirota (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 (Lo Curto et al. 2011).
The L. casei Shirota strain was selected and cultivated because of its ability to survive the harsh conditions of the gut. There are several research papers describing human studies showing the survival of L. casei Shirota, encompassing a mix of population groups and a variety of ages, geographical locations and health conditions (see recommended further reading below).
Survival of L. casei Shirota through the gut - Spanhaak et al. (1998) Eur J Clin Nutr 52:899-907
Method: This double-blind, placebo-controlled, randomised trial in the Netherlands involved 20 healthy adult men drinking either 3 x 100ml a day of fermented milk containing 109 CFU L. casei Shirota per ml, or the same quantity of an unfermented milk placebo, for 4-weeks. Faecal samples were collected throughout the trial to assess the human gut survival of L. casei Shirota.
Results: L. casei Shirota was detected at significantly increased levels in the faeces of subjects in the treatment group during the intervention period, compared to the placebo group (P < 0.01). In the treatment group, L. casei Shirota was detected at levels reaching 107 CFU/g of wet faeces. Once ingestion of LcS had ceased, levels decreased and reverted back to their pre-intervention state. Additionally, in only those consuming L. casei Shirota, there was a significant increase in Bifidobacterium (P < 0.05).
Recommended Further Reading
Other examples of studies that have shown survival of L. casei Shirota include, but are not limited to, studies conducted in healthy adults within European populations (Tilley et al. 2014, Tuohy et al. 2007) as well as several Asian populations (Mai et al. 2017, Utami et al. 2015, Wang et al. 2015a), elderly populations (Bian et al. 2011), pre-school and school-age children (Wang et al. 2015b) and critically ill children (Srinivasan et al. 2006).