How does one calculate the nutrition of homemade yogurt? I'm using 2% milk and a packet of yogurt culture. Does anything change during cooking that makes the nutrition info of the final product any different than the milk I use? Does yogurt culture have calorie, fat, carb, etc content?

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The answer is that they are not much different.

During fermentation, some of the milk's lactose is converted by bacteria into protein and other substances. The amount of conversion is pretty insignificant in terms of calories and grams of macronutrients. The most important effects are the changes in taste and consistency and the presence of live bacteria. Usually many of the bacteria survive the highly acid stomach fluids to reach the small intestine where they continue digesting lactose.

Fitday.com gives the info below for a cup of each, which may be surprising at first. However, commercial yogurt tends to be more dense than milk, as you might see if you make it at home: a cup of milk gives you some watery fluid floating on top of less than a cup of yogurt.

```Food              | Calories | Fat  | Carbohydrates | Protein
------------------+----------+------+---------------+--------
Whole Milk Yogurt | 149 kcal | 8.0g | 11.4g         | 8.5g
Whole Milk        | 146 kcal | 7.9g | 11.0g         | 7.9g
```
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The answer, like all good answers, is that it depends. Do you remove anything when you make homemade yogurt from the vessel in which you make it (crock pot, pot, yogurt maker, etc)? When I make yogurt I have to pour off some water that floats to the top, which means there are more nutrients in each serving than there would be if I divided the original 2% milk by the same amount as I do my yogurt.

During the production of yogurt the bacteria will be eating some of the sugars in the milk while they do their work, but the difference in nutrition is fairly small.

General nutrition facts for whole milk yogurt and whole milk indicate that there is a pretty negligible difference between the two. In general you can take the calorie contents of your ingredients, divide by the number of servings, and get calories per serving.

In terms of nutrition the biggest difference is the live cultures that are in your homemade yogurt. The current general consensus is that these live cultures are good for a variety of things in the human body.

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Yogurt making is a pretty gentle process - the bacteria involved do consume some of the natural milk sugars (and then excrete lactic acid, which in turn curdles the milk solids which thickens the texture) - but the carbohydrate drop is pretty minimal. If I was making yogurt from store-bought milk, I'd use the nutrition information on the side of the carton.

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