Mixed
Metchnikoff's historical theory that consuming yogurt (Lactobacillus bulgaricus) delays senility and extends life is scientifically unvalidated and based on a mechanism (L. bulgaricus surviving in the human intestine) that subsequent research disproved.
Do not rely on Lactobacillus bulgaricus (found in traditional yogurt) to extend your lifespan or delay aging. While a healthy lifestyle is important, this specific probiotic does not survive in the human gut, and Metchnikoff's longevity claims were never scientifically validated. Focus on evidence-based health practices instead.
The efficacy of his treatment in retarding the onset of senility was never validated scientifically. Moreover, subsequent work by a host of investigators showed that L. bulgaricus is unable to survive in the human intestine or that of any other animal studied and, hence, not capable of replacing putrefactive bacteria in the colon (6).
Why this rating
The paper cites historical validation attempts and subsequent microbiological studies showing L. bulgaricus cannot survive in the gut.
Source
Recycling Metchnikoff: Probiotics, the Intestinal Microbiome and the Quest for Long Life
Philip A. Mackowiak · Frontiers in Public Health · 2013
This is one finding among thousands. Every one is graded and traced to its source, so you can see what the evidence actually supports. Browse the research →