Real vs fake kefir: let’s talk lactose!

There’s a big difference between real, traditionally fermented kefir made using live kefir grains, and the more commercialised versions often found on supermarket shelves. These store-bought versions are typically made with simplified starter cultures, and the difference goes far beyond flavour.

Natural kefir grains themselves are quite special – they contain a complex community of microorganisms, including lactic acid bacteria, acetic acid bacteria, and natural yeasts.¹ The diverse and balanced microbiota work synergistically during fermentation.

In contrast, kefir starter cultures used in industrial production often contain only a limited number of microbial strains and may lack the characteristic species typically found in real kefir grains. As a result, the microbial activity and, therefore, the nutritional and functional quality of commercial kefir is often much lower.

One of the key differences this creates? Lactose content and total sugars.

The real deal: why traditional kefir is low in lactose

The natural community of microbes including yeasts feed on lactose, the natural sugar found
in milk, and break it down using an enzyme called β-galactosidase.

Here’s what happens:

Lactose is broken into simpler sugars, glucose and galactose, which fuel microbial growth.
As the microbes grow, they produce Galacto-oligosaccharides (GOS) – a type of prebiotic, or non-digestible carbohydrate that serves as food for beneficial gut bacteria.
GOS has been shown to support gut health and modulate the gut microbiota and the immune system.²

What happens to the lactose?

Let’s break it down:

Starting milk: 5.58 g of lactose per 100 mL
After 18 hours of fermentation: 2.12 g → a 62% reduction
After 7 days of storage: 0.8g → an 86% total reduction

These findings come from a study³ examining lactose reduction during the natural fermentation of kefir using traditional grains. Importantly, lactose continues to be broken down even after the kefir is bottled and stored, thanks to ongoing microbial activity.

This explains why traditionally fermented kefir is often well tolerated, even by individuals with lactose intolerance.⁴

What about commercial or “fake” kefir?

Many commercial kefir products are made with direct-set starter cultures – a simplified mix of bacteria without the full range of microbes found in traditional grains. These products often:

Contain fewer bacterial species, especially naturally occurring yeasts
Ferment milk less thoroughly
Leave behind higher levels of lactose and sugar
Lack many of the prebiotic and probiotic benefits found in traditionally fermented kefir

For comparison:

A typical plain supermarket kefir contains around 8–10 g of sugar per 200 mL serving.
In contrast, traditionally fermented kefir (such as those made with live grains) can contain as little as 2.7 g of sugar per 170 mL – a reflection of the extensive microbial fermentation and lactose breakdown.

The takeaway

If you’re looking for a kefir that is:

Naturally lower in lactose
Rich in microbial diversity
Supportive of gut health and immune function
A source of natural prebiotics like GOS

…then traditionally fermented kefir made with real kefir grains is the clear choice.

The science supports it and so does your gut!

For the full low-down, make sure you read REAL kefir vs FAKE kefir: 10 key differences!

Any questions? Contact one of our Nutritional Therapists via live chat, weekdays from 8 am to 8 pm.

Real vs fake kefir: let’s talk lactose!

The real deal: why traditional kefir is low in lactose

What happens to the lactose?

What about commercial or “fake” kefir?

The takeaway

References

Questions? Talk to a Nutritional Therapist on live chat!

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