Kefir: Nutrition, Lactose, Probiotics and How to Use

By Nikola · Precision Nutrition L1 · Updated 4 November 2026

Kefir is a sour, slightly fizzy fermented milk drink made with kefir grains, small clusters of bacteria and yeasts that ferment the milk. The low-fat kefir in the USDA database gives 52 kcal, 3.6 g of protein and 124 mg of calcium per 100 g, so one cup (244 g) covers close to 40% of the EU reference intake for calcium. In a small trial, kefir caused far fewer symptoms than milk in adults who digest lactose poorly. It is a fermented food with live microbes, but that does not make every kefir a proven probiotic.

Kefir nutrition per 100 g and per portion

Nutrient	Kefir (low-fat), 100 g	Portion: 1 cup (244 g)
Energy	52 kcal	127 kcal
Protein	3.6 g	8.8 g
Fat	1.0 g	2.3 g
of which saturated	0.6 g	1.5 g
Carbohydrate	7.5 g	18.3 g
of which sugars	6.9 g	16.9 g
Calcium	124 mg	303 mg
Phosphorus	100 mg	244 mg
Potassium	159 mg	388 mg
Riboflavin (B2)	0.17 mg	0.42 mg
Vitamin B12	0.3 µg	0.73 µg
Selenium	3.6 µg	8.8 µg
Sodium	38 mg	93 mg

Source: USDA FoodData Central, “Kefir” (FNDDS), FDC ID 2705394, checked 4 November 2026. This record describes a low-fat kefir with 0.96 g of fat per 100 g; kefir made from whole milk has more fat and energy, so check the label of your brand. The record gives 1 cup = 244 g; the portion column is calculated. Values rounded.

Per 100 g this kefir gives about 15% of the EU reference intake for calcium (800 mg), 14% for phosphorus (700 mg), 12% for riboflavin (1.4 mg) and 12% for vitamin B12 (2.5 µg). A cup gives about two and a half times that.

Glycemic index of kefir

Kefir is not listed in the international GI tables (Atkinson 2008). For comparison, the same tables give full-fat milk a GI of 39 ± 3 and fruit yogurt 41 ± 2. These are only reference points: kefir itself has no measured value in the tables, and flavoured kefirs with added sugar are a different product.

Health benefits: what the evidence says

Calcium for bones. With 124 mg of calcium per 100 g, kefir is a source of calcium under EU rules, and the EU permits the claim that calcium is needed for the maintenance of normal bones (Regulation (EU) No 432/2012).
Lactose maldigestion. In a study of 15 adults with lactose maldigestion, a test meal with 20 g of lactose as kefir or yogurt produced much less breath hydrogen than milk, and flatulence was 54-71% lower; pain and diarrhoea were negligible. The authors concluded that kefir may be another strategy for people with lactose intolerance (Hertzler and Clancy, 2003). It was a small, short study, so treat it as encouraging rather than conclusive.
Live microbes, limited proof. Kefir is a fermented food. The ISAPP consensus on fermented foods notes that milk kefir is among the few fermented foods tested in at least one randomised trial, but it also stresses that “fermented food” and “probiotic” are not interchangeable: a probiotic requires defined strains, proven safety and a demonstrated benefit. Claims that kefir fixes digestion, immunity or weight go beyond the evidence.
Protein in a drink. A cup gives almost 9 g of protein, which makes kefir a practical part of breakfast or a snack after exercise.

Ayurveda: kefir in the traditional system

Kefir does not appear in Usha and Vasant Lad’s food guidelines. The closest entries are buttermilk, favourable for Vata, to be avoided for Pitta and favourable in moderation for Kapha, and plain yogurt, which is on the list to avoid for all three doshas, while diluted yogurt is favoured. Kefir is thinner and sourer than yogurt, so it sits somewhere between the two, but this is our analogy, not a direct entry. It is a traditional view, not a clinical finding.

How to buy and use kefir

Read the label. Plain kefir should list milk and kefir cultures. Flavoured kefirs often contain added sugar.
Fat content: low-fat and whole-milk kefirs differ in energy; choose what fits the rest of your diet.
Breakfast: pour kefir over oats the night before, or stir in chia seeds and leave them to swell.
Smoothies: blend kefir with blueberries or a banana instead of milk or juice.
Savoury: use it in cold cucumber and dill soup, as a base for salad dressings, or in marinades for chicken.
Heat: heating kills the live microbes, so for cultures drink kefir cold or add it at the end.
Storage: keep it in the fridge and use it by the date on the pack.

Who should be careful

Milk allergy. Kefir is a milk product and contains milk proteins. It is not suitable for people with cow’s milk allergy. Milk allergy and lactose intolerance are different conditions.
Severe lactose intolerance. Kefir still contains lactose. Many people with lactose maldigestion handle it better than milk, but start with a small glass.
Weakened immune system. NCCIH notes that the risk of harm from probiotics is greater in people with severe illness or compromised immunity. If this applies to you, ask your doctor before drinking products with live cultures.
Added sugar. Sweetened kefirs can contain a lot of sugar. WHO recommends keeping free sugars below 10% of daily energy.

FAQ

What is the difference between kefir and yogurt?

Both are fermented milk. Yogurt is made with a few bacterial strains and is thick and spoonable; kefir is made with kefir grains that contain bacteria and yeasts, and it is thinner, sourer and slightly fizzy. Compare fat, protein and sugar on the labels, which vary a lot between brands.

Can I drink kefir if I am lactose intolerant?

Many people can. In a small study, adults with lactose maldigestion had much less breath hydrogen and flatulence after kefir than after milk. Kefir still contains lactose, so start with a small amount and see how you feel.

Is kefir a probiotic?

Kefir contains live microbes, but scientists reserve the word probiotic for defined strains with a proven health benefit. Kefir has been tested in a few trials; it is a good fermented food, not a guaranteed treatment.

Sources

USDA FoodData Central: Kefir, FNDDS (FDC ID 2705394). fdc.nal.usda.gov
Regulation (EU) No 1169/2011, Annex XIII – nutrient reference values. EUR-Lex
Commission Regulation (EU) No 432/2012, list of permitted health claims (calcium). EUR-Lex
Hertzler SR, Clancy SM. Kefir improves lactose digestion and tolerance in adults with lactose maldigestion. J Am Diet Assoc 2003;103(5):582-587. PubMed
Marco ML, Sanders ME, Gänzle M et al. The International Scientific Association for Probiotics and Prebiotics (ISAPP) consensus statement on fermented foods. Nat Rev Gastroenterol Hepatol 2021;18:196-208. nature.com
NCCIH: Probiotics: usefulness and safety. nccih.nih.gov
World Health Organization: Healthy diet, fact sheet. who.int
Atkinson FS, Foster-Powell K, Brand-Miller JC. International tables of glycemic index and glycemic load values: 2008. Diabetes Care 2008;31(12):2281-2283. PMC
Lad U, Lad V. Food Guidelines for Basic Constitutional Types, from Ayurvedic Cooking for Self-Healing, 2nd ed. The Ayurvedic Institute. ayurveda.com

This page is for information only and is not medical or dietary advice.

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