Kefir

Kefir is milk fermented by a community of bacteria and yeasts that live together in rubbery grains. It is the most diverse fermented food in the ordinary supermarket — thirty to sixty strains against yoghurt's two or three — and it is the base of the 50 Man Foods breakfast smoothie.

It tastes like sour, faintly fizzy yoghurt you can drink. Most of the lactose is gone by the time it reaches you.

  • Daily
  • 1 recipe
  • Fermented dairy
  • Updated Sep 2026

What it supplies

Nutrient · per 100 g (a little under half a cup) Amount % DV Relative amount
Calcium 130 mg 10%
Protein 3.3 g 7%
Vitamin B12 0.29 mcg 12%
Riboflavin 0.14 mg 11%
Fat 3.5 g 4%
Live cultures 30–60 strains 0%

Source: USDA FoodData Central.Percent Daily Values are based on adult reference intakes. The bars stop at 100%; the numbers do not.

Why it works

A gut is an ecosystem, and diversity is what makes an ecosystem stable. Kefir's mixed culture colonises more transiently than a single-strain probiotic but shifts the whole community, and trials show improvement in lactose tolerance, H. pylori eradication rates and constipation.

It also delivers milk's calcium and protein in a form people who cannot drink milk usually tolerate, which keeps dairy in a diet that would otherwise lose it.

How much, how often

  • 1 cup

    Daily

    Regularity matters more than volume; start with half a cup if fermented food is new.

  • Plain, whole milk

    Never heated

    Flavoured kefir is a soft drink with cultures; heat kills the cultures.

How to buy and prepare it

Whole milk, plain, grass-fed where possible. The label should list the strains and say live and active cultures. Flavoured kefir carries as much sugar as a soft drink. Water kefir is a different ferment with no dairy and far less to offer.

Making it yourself is easy and cheaper: a tablespoon of grains in a jar of milk on the counter for a day.

Drink it plain, or blend a cup with a mango, an egg yolk and a spoon of honey for the smoothie. Do not heat it; heat kills the cultures. Strained through cloth it becomes a soft cheese.

Refrigerated, it keeps to its date and then grows sharper rather than spoiling. Home kefir keeps two to three weeks cold and continues to ferment slowly. Grains rest in fresh milk in the fridge for a week between batches.

Recipes that use it

In these guides

Questions

Kefir or yoghurt?
Kefir, for diversity — ten to twenty times the strains, including yeasts — and because it is drinkable. Yoghurt is still a good food; kefir is a better probiotic.
How much a day?
A cup. More is fine but the benefit comes from regularity rather than volume. Start with half a cup if your gut is not used to fermented food.
Can I drink it if I am lactose intolerant?
Usually yes. The cultures consume much of the lactose and supply lactase; most lactose-intolerant people tolerate kefir well, and regular use improves tolerance.