Nobel Prize winner Élie Metchnikoff believed eating yogurt could extend human life to 140 years.

Élie Metchnikoff was a Russian zoologist and immunologist who won the Nobel Prize in Physiology or Medicine in 1908 for his work on phagocytosis. During his later years at the Pasteur Institute in Paris, he became obsessed with the concept of orthobiosis, which is the idea of living a full and healthy life to its natural limit. He published his theories in the 1907 book 'The Prolongation of Life: Optimistic Studies', where he argued that aging was caused by 'autointoxication' from putrefactive bacteria in the large intestine.Metchnikoff's research focused on the rural populations of Bulgaria and the Russian Caucasus, where he noted a high concentration of centenarians. He discovered that these populations consumed large quantities of fermented milk containing a specific bacterium identified by Bulgarian student Stamen Grigorov in 1905. This bacterium was later named Lactobacillus bulgaricus. Metchnikoff hypothesized that these beneficial microbes would create an acidic environment in the gut, preventing the growth of harmful bacteria that produce toxins.To test his theory, Metchnikoff began consuming sour milk every day and encouraged the public to do the same. This sparked a global health craze and effectively founded the probiotic industry. While modern science has debunked his claim that humans could live to 140 simply by eating yogurt, his work laid the foundation for contemporary research into the gut microbiome. Today, scientists recognize the vital role of gut flora in immune function and overall health, validating Metchnikoff's status as the 'father of probiotics'.