What is it? Kefir is a fresh, cultured-milk product typically served as a creamy drink that is as thick as a milk shake. It originated in the Middle East and is now becoming more widely available. Its flavor, similar to that of yogurt, is mild and slightly tart.
The general concensus from my team is home made kefir contains 4 grams per cup (8oz) , so 1/2 cup (4 oz) would be 2 carbs = to 1/2 teaspoon of sugar. Now with that said commercially made kefir can run a higher count as much as double, here's a nutritional label from a commercial product;
Kefir (low-fat, plain), 1 cup (227g)
Calories: 160
Protein: 14g
Carbohydrate: 8g
Total Fat: 2.5g
Fiber: 0.0g
If it was me I'd play it on the safe side and count 1/2 cup of your home made kefir as 4 carbs. Remember, active
weight loss is maintained at 20 carbs or less per day.