Uploaded February 2025 | Updated September 2026, 2 weeks ago
Yogurt has been around ever since animals were first domesticated in Mesopotamia around 7000 years ago and naturally occurring bacteria of the Lactobacillus species drifted into warm milk and thickened it. Enzymes produced by the bacteria convert lactose, the naturally occurring sugar in milk, into lactic acid that in turn causes precipitation of protein in the milk producing a thick texture. Not only did people find the sour taste of the acid appealing, they also discovered that the fermented milk lasted longer. Now we know that lactic acid prevents the growth of bacteria that can cause spoilage.
The ancient Greeks and Romans took to yogurt as apparently did Genghis Khan who fed yogurt made from mare’s milk to his army. It was likely wandering Turks who introduced yogurt to Europe where it became a staple in the Balkans. Entry into the world of “health foods” came when future Nobel laureate Elie Metchnikoff hypothesized, without evidence, that the supposed longevity of Bulgarian peasants was due to their frequent consumption of yogurt. On a visit to Metchnikoff’s lab in Paris, Dr. John Harvey Kellogg of cereal fame saw a pitcher of yogurt on Metchnikoff’s desk and when asked about it was informed of its potential benefits. He took this to heart, and on his return to the “Sanitarium” he had founded in Battle Creek, Michigan, he began using it as a form of treatment. Kellogg encouraged the consumption of yogurt, but believed that its most effective use was as an enema.
Metchinkoff’s suggestions about the health benefits of yogurt pretty well flew under the radar until the 1990s when research blossomed about the bacteria that inhabit our gut, the microbiome. It turns out that these microbes are not just inactive bystanders but can affect our physiology. This is exemplified by a recent study by Harvard researchers that scrutinized dietary data and cancer statistics collected over years from some 150,000 health professionals. Just over a thousand colon cancer cases were identified in which tumours had been analyzed for the presence of bacteria. Bifidobacteria were absent in about twice as many tumours as in ones where they were present which led the researchers to conclude that these bacteria offered protection against colon tumours. They further suggested that this protection was linked to consuming more than two servings of yogurt a week.
As can be expected this generated a lot of media attention. What was mostly left out of the coverage, however, was that there were no statistically significant associations between long-term yogurt intake and overall colorectal cancer incidence! So, bifidobacteria may reduce the risk of some tumours but not the overall risk of colorectal cancer, which is what we are really interested in. Furthermore, not all yogurts contain bifidobacteria. They are all made with some form of lactobacillus, but only some producers add bifidobacteria. There is also the question of how many of the live bacteria are actually contained in the product and how many make it to the gut. If yogurt really increases longevity as Metchnikoff insinuated, it is not by preventing colon cancer.
Yogurt has been around ever since animals were first domesticated in Mesopotamia around 7000 years ago and naturally occurring bacteria of the Lactobacillus species drifted into warm milk and thickened it. Enzymes produced by the bacteria convert lactose, the naturally occurring sugar in milk, into lactic acid that in turn causes precipitation of protein in the milk producing a thick texture. Not only did people find the sour taste of the acid appealing, they also discovered that the fermented milk lasted longer. Now we know that lactic acid prevents the growth of bacteria that can cause spoilage.
The ancient Greeks and Romans took to yogurt as apparently did Genghis Khan who fed yogurt made from mare’s milk to his army. It was likely wandering Turks who introduced yogurt to Europe where it became a staple in the Balkans. Entry into the world of “health foods” came when future Nobel laureate Elie Metchnikoff hypothesized, without evidence, that the supposed longevity of Bulgarian peasants was due to their frequent consumption of yogurt. On a visit to Metchnikoff’s lab in Paris, Dr. John Harvey Kellogg of cereal fame saw a pitcher of yogurt on Metchnikoff’s desk and when asked about it was informed of its potential benefits. He took this to heart, and on his return to the “Sanitarium” he had founded in Battle Creek, Michigan, he began using it as a form of treatment. Kellogg encouraged the consumption of yogurt, but believed that its most effective use was as an enema.
Metchinkoff’s suggestions about the health benefits of yogurt pretty well flew under the radar until the 1990s when research blossomed about the bacteria that inhabit our gut, the microbiome. It turns out that these microbes are not just inactive bystanders but can affect our physiology. This is exemplified by a recent study by Harvard researchers that scrutinized dietary data and cancer statistics collected over years from some 150,000 health professionals. Just over a thousand colon cancer cases were identified in which tumours had been analyzed for the presence of bacteria. Bifidobacteria were absent in about twice as many tumours as in ones where they were present which led the researchers to conclude that these bacteria offered protection against colon tumours. They further suggested that this protection was linked to consuming more than two servings of yogurt a week.
As can be expected this generated a lot of media attention. What was mostly left out of the coverage, however, was that there were no statistically significant associations between long-term yogurt intake and overall colorectal cancer incidence! So, bifidobacteria may reduce the risk of some tumours but not the overall risk of colorectal cancer, which is what we are really interested in. Furthermore, not all yogurts contain bifidobacteria. They are all made with some form of lactobacillus, but only some producers add bifidobacteria. There is also the question of how many of the live bacteria are actually contained in the product and how many make it to the gut. If yogurt really increases longevity as Metchnikoff insinuated, it is not by preventing colon cancer.
