Kefir: what it is, its real benefits and how to have it

What does a serving of milk kefir provide?

The nutritional composition of kefir varies depending on the milk and how it is made. The table gives approximate values per 100 g and per 200 g glass; check the label of the specific product. The European database [1] is a general reference.

Nutrient	Per 200 g	Per 100 g
Protein	7 g	3.5 g
Calcium	240 mg	120 mg
Sugars	6.2 g	3.1 g
Vitamin D	0 µg, unless fortified	0 µg

Residual lactose varies: one study found between 2 and 3.4 g per 100 g, depending on the milk used [2]. The sugars line on the label does not, by itself, tell you how much lactose remains.

What does the evidence say about kefir’s benefits?

Studies in people are still small and use different drinks, amounts and durations. A review of 16 trials found signals for only a few outcomes, such as a possible benefit alongside treatment for Helicobacter pylori or a reduction in cholesterol [4]. Most of those studies had a high risk of bias, and the authors called for better trials before making recommendations [4].

For the gut microbiota, a recent review found modest and varied changes. Finding kefir microorganisms in stool does not, on its own, show that symptoms have improved [3]. If you want to take care of your diet as a whole, read what to eat to care for your gut microbiota.

Laboratory findings about kefir microbes or substances do not support claims that it prevents infections or boosts immunity in people [4]. Nor is there a universal amount with proven clinical effectiveness. If digestive symptoms keep recurring, it is worth investigating their cause.

How are milk kefir and water kefir different?

Milk kefir is made from dairy and retains protein, calcium and a variable amount of lactose [1][2]. Water kefir ferments a sugary mixture; its final composition depends on the recipe and fermentation time [5].

Water kefir is not nutritionally equivalent to a dairy product. It may retain sugar and produce alcohol during fermentation. There is no safe amount of alcohol for health (WHO): the less, the better, and none during pregnancy, breastfeeding or childhood, before driving, or if your medication does not allow it. The Irish food safety authority found undeclared alcohol in some unpasteurised fermented plant-based drinks [5]. Check the label if you want to avoid sugar or alcohol.

Homemade kefir: hygiene and fermentation

To make homemade kefir, use pasteurised milk and clean utensils. Follow the instructions for a reliable culture and refrigerate the drink when fermentation is complete [6]. If you see mould, notice an unusual bad smell or have doubts about how it was stored, discard it.

For water kefir, do not seal a container airtight while it is fermenting. Gas can build up and increase pressure, and alcohol may continue to form during storage [5]. If you are thinking of giving it to a child, read our guide to kefir for children.

How much kefir should you have, and how can you include it?

There is no required daily amount of kefir. If you like it and tolerate it, have it as one of your usual dairy foods. A simple option is to mix it with fruit or use it as the base for a cold sauce.

Choose plain kefir if you prefer to decide how much to sweeten it. In a study of product labels in Poland, most plain varieties had fewer carbohydrates than flavoured ones [7]; check the label of the product you buy.

Can someone with lactose intolerance have it?

Tolerance varies from person to person. Fermentation reduces some of the lactose, but conventional milk kefir may still contain it [2]. If you want to avoid lactose, check that the package says “lactose-free”. Our guide to lactose intolerance explains how to plan the rest of your diet.

Tolerating a product does not show that kefir treats lactose intolerance [4].

Who should take extra care?

If you are immunocompromised, avoid raw milk and ask your medical team before having homemade fermented products. Unpasteurised foods carry a higher risk of transmitting illness-causing microorganisms, as the CDC food safety advice reminds us [6]. A commercial product made with pasteurised milk is a more controlled option.

If you have diabetes and use insulin or medicines that can lower your blood sugar too much, check the carbohydrates on the package. Dietary choices do not replace adjustments made by your doctor [8]. If you are also managing your cholesterol, see our guide to high cholesterol.

What questions come up in consultations?

A more sour taste does not tell you how much lactose kefir contains: check the product information [2]. There is also no evidence that having it on an empty stomach improves its effects; have it whenever it suits you.