Natural yogurt, Greek yogurt, skyr, kefir and buttermilk are often found next to one another in the supermarket.
They are all cultured or fermented dairy foods, but they are not the same product.
They differ in how they are made, their texture, nutritional composition and the microorganisms involved in fermentation.
Natural yogurt
Natural yogurt — plain, unsweetened yogurt — is produced by fermenting milk with characteristic yogurt bacteria.
These bacteria convert some of the lactose in milk into lactic acid. This creates yogurt’s characteristic acidity and helps produce its texture.
Natural yogurt provides protein and calcium and may contain live bacterial cultures when consumed.
Plain natural yogurt is also nutritionally different from many flavored yogurts, which may contain added sugar.
Greek yogurt
Greek yogurt is traditionally produced by straining yogurt to remove part of the liquid whey.
This creates a thicker and more concentrated product.
Greek yogurt is typically higher in protein than standard natural yogurt. Its fat content can vary considerably between products.
Products described as Greek-style yogurt are not necessarily produced using traditional straining and may achieve their texture through different manufacturing methods.
Skyr
Skyr originated in Iceland.
Although it is commonly sold and eaten like yogurt, traditionally it is closer to a cultured fresh cheese.
It is typically thick, high in protein and often relatively low in fat.
Its high protein content is one of the main nutritional characteristics that distinguishes skyr from many conventional yogurts.
Kefir
Kefir is a fermented milk drink produced through a different fermentation process.
Traditional kefir involves a complex microbial community containing both bacteria and yeasts.
This gives kefir a different microbial profile from conventional yogurt, which is produced using defined bacterial starter cultures.
Kefir is usually thinner than yogurt and has a characteristic acidic taste.
Commercial products can differ from traditionally fermented kefir, so their microbial composition may also differ.
Buttermilk
Buttermilk means maślanka.
Traditional buttermilk was the liquid remaining after cream was churned to produce butter.
Most buttermilk sold today is cultured buttermilk, produced by fermenting milk with selected bacterial cultures.
It is therefore a separate fermented dairy product and should not be considered another name for kefir or yogurt.
Which differences matter nutritionally?
These products can offer different nutritional characteristics.
Greek yogurt and skyr are typically higher in protein, which can make them useful when a higher protein intake is a priority.
Yogurt as a broader category has more direct long-term observational evidence. Higher yogurt consumption has been associated with lower all-cause mortality. Current research does not establish whether this association differs between natural yogurt, Greek yogurt or other types of yogurt.
Kefir is distinctive because its traditional fermentation involves a diverse microbial community, including bacteria and yeasts.
This does not mean that current research has established one of these products as superior for healthy aging.
The long-term evidence for yogurt does not tell us whether natural yogurt, Greek yogurt, skyr, kefir or buttermilk provides the greatest longevity benefit.
When choosing between them, the actual nutritional composition remains important. Protein, fat, added sugar and ingredients can vary substantially between individual products.
