Fermented dairy likely developed independently across several pastoral cultures in Central Asia and the Middle East thousands of years ago, probably discovered by accident when milk carried in animal-skin containers fermented naturally in warm climates. It became a dietary staple across an enormous geographic range, each region developing its own distinct fermentation traditions.
Yogurt's modern scientific reputation owes a considerable debt to Russian Nobel laureate Élie Metchnikoff, whose early 20th-century observations of long-lived, yogurt-consuming Bulgarian peasants helped launch the entire modern field of research into fermented foods and gut health.
Fermented dairy has real, replicated evidence for blood pressure specifically. Multiple independent meta-analyses have found significant reductions: one review of 9 trials (543 participants) found probiotic consumption, mostly via fermented dairy, significantly reduced systolic blood pressure by 3.56 mmHg and diastolic by 2.38 mmHg, and a separate meta-analysis of 14 trials found similar reductions. Worth flagging transparently: one prominent meta-analysis on this exact topic was subsequently retracted, a genuine red flag worth weighing, even though it doesn't invalidate the other independently-conducted positive reviews.
For blood sugar management specifically, the picture is more clearly negative: a meta-analysis of 9 randomized controlled trials found no significant benefit of probiotic yogurt on HbA1c, fasting glucose, or insulin resistance in people with type 2 diabetes or obesity. This split — real, replicated blood pressure benefit (with one important retraction noted) but explicitly no benefit for glycemic control — is why "Limited-Moderate" is the accurate, honest rating.
Milk fermented with live bacterial cultures over hours to days, depending on the specific style and desired thickness/tartness.