There has been much made of probiotics regulating digestive health in the news and repeatedly hawked by people sharing the benefits of yogurt with special bacteria that will change your life. I was advised by my mother that when I was taking antibiotics, eating yogurt would help counteract some of the negative consequences of oral antibiotics and repopulate my gastrointestinal tract with beneficial bacteria. But I was unaware of research published in Bioscience, Biotechnology, and Biochemistry showing that yogurt with Lactobacillus gasseri could actually heal acid-induced ulcers—at least in rats.
Uchida, Shimizu and Kurakazu examined how well live yogurt cultures with Lactobacillus gasseri OLL 2716 (LG21 yogurt from Meiji Dairies Corporation where the researchers are employed) could heal chronic gastric ulcers. Male Sprague-Dawley rats had ulcers induced by spot treatment of the stomach with acetic acid to simulate a chronic ulcer. Three days after this treatment, the rats were fed LG21 yogurt, γ-irradiated LG21 (to kill the bacteria in the yogurt) or distilled water, the control treatment, twice a day for ten days. The rats were sacrificed and the size of ulcer in the stomach measured. The LG21 yogurt with active Lactobacillus made a difference in the size of the ulcers. Ulcers from rats fed LG21 yogurt were a third of the size (2.9mm) compared to ulcers from rats treated with either distilled water or γ-irradiated LG21 yogurt.
With evidence of improved ulcer healing after rats consumed LG21 yogurt, the researchers decided to examine how well LG21 yogurt could protect against acute ulcers. This experiment was performed by feeding rats LG21 yogurt, γ-irradiated LG21 or distilled water 30 minutes before administering hydrochloric acid (HCl). An hour after HCl treatment, the rats were sacrificed and the resulting stomach lesions examined. Interestingly, both LG21 and γ-irradiated LG21 yogurt showed significant effects on the number of lesions found in rat stomach. In fact, 5ml yogurt/kg rat treatment level was more than five times as effective than the 2.5ml/kg treatment, which due to variation in control numbers, did not have a significant difference compared to control treatment. The 5ml/kg LG21 and γ-irradiated LG21 yogurt treatment exerted a strong protective effect by minimizing the presence of lesions to nearly nothing, less than 5mm of lesions versus control treatment of 59.9mm of lesions.
Expression of prostaglandin E2 is known to protect gastric mucosa so Uchida, Shimizu and Kurakazu examined the levels of prostaglandin E2 present in rats treated with HCl. Gastric mucosa tissue was removed from rats pretreated with water, LG21 or γ-irradiated LG21 yogurt before HCl treatment, minced and the resulting supernatant tested for levels of prostaglandin E2 using an enzyme immunoassay. While LG21 yogurt demonstrated a modest but not significant increase in levels of prostaglandin E2 compared to control, the γ-irradiated LG21 yogurt showed a significant increase in prostaglandin E2 expression compared to control treatment.
This set of experiments gave intriguing answers to the question of the protective effect of yogurt on ulcers in rats. While the presence of live cultures was needed for healing in the chronic ulcer model, the acute ulcer model demonstrated that yogurt with or without live bacteria was able to protect against induction of ulcers. Furthermore, the γ-irradiated LG21 yogurt demonstrated that live yogurt cultures are not necessary for increased prostaglandin E2 expression, another protective mechanism against ulcers, nor needed to prevent ulcer formation. While I would not go as far to say that yogurt manufacturers have found a new angle with which to advertise the benefits of yogurt, this research certainly suggests there is more to yogurt than its live cultures.
Uchida, M., Shimizu, K. & Kurakazu, K. (2010). Yogurt Containing Lactobacillus gasseri OLL 2716 (LG21 yogurt) Accelerated the Healing of Acetic Acid-Induced Gastric Ulcer in Rats, Biosci. Biotechnol. Biochem. 74, 1891–4. DOI: 10.1271/bbb.100287