It seems as though it should be simple: Read the label and there's the carb count. Or even, knowing that yogurt is just milk with bacteria added, figuring that plain yogurt should have the same amount of carbohydrate as the milk is was made from. This makes perfect sense, but it turns out to be wrong.
Yogurt is one of the more confusing foods when it comes to carbs. Here is part of an email I received: "I was trying to watch my carbs and also going with some other report that yogurt could help you lost weight -- specifically belly fat. So here I was eating my ½ cup of plain non fat yogurt morning and evening...come to find out there is 19 carbs per serving. I was sabotaging myself. So where does yogurt fit in? And where does 19 grams of carbs come from in plain tart yogurt?"
There are three issues when it comes to carbohydrates and yogurt:
1. Stuff is Added to YogurtYes, even plain yogurt often has added ingredients that increase carbs. In the case of this reader, it was almost certainly nonfat milk powder, which is often added to thicken up nonfat yogurt. Milk has lactose, and powdered milk is going to have a greater concentration of it. Lactose is a kind of sugar, hence, added carbs. Moral: Read the label carefully.
2. The Bacteria That Makes Yogurt Dines On LactoseBut wait, there's also good news. It turns out that when you introduce the bacteria that makes yogurt (this is also true of kefir) it eats up much of the lactose, thus reducing the amount of sugar in the final product. This was confirmed by Dr. Jack Goldberg, co-author of the GO-diet and the Four Corners Diet, who has done extensive testing of fermented milk products. He found that up to 8 grams of carbohydrate are consumed by the bacteria in a cup of yogurt, kefir, or buttermilk that contains live cultures. Under ideal circumstances, this would reduce the 12 grams of carb in a cup of milk to 4 or so grams of carb.
How much carbohydrate can we subtract? Two factors are involved in how much lactose gets eaten by the bacteria. First, you must determine that live cultures are in the yogurt. This does not mean that the yogurt was "made with" live cultures; by definition all yogurt is made that way. If the yogurt says on the label that it was "made with" live cultures, you can bet that those cultures are not living now. After the bacteria are killed, the carbohydrate level becomes stable. So you want the label to say that the yogurt "contains" live cultures, with the names of at least two kinds of bacteria (and the more the better), such as lactobacillus acidophilus, bifidus, or l. casei.
The second factor that makes a difference in this process has to do with how long the yogurt is left to ferment. Although the process continues slowly after chilling, the vast majority happens in the stage where the yogurt is kept warm. Most commercial yogurt does not ferment long enough for the maximum amount of lactose consumption by the bacteria. Dr. Goldberg says that most commercial yogurt with live cultures has 7 to 8 grams of carbohydrate per cup, but that that amount will continue to slowly diminish over time, even after purchase. He also says that by the time the carbohydrate decreases to about 4 to 5 grams per cup, the amount stabilizes because so much lactic acid has been produced that the bacteria go dormant. If you make your own yogurt, it may take as long as 20 hours to get to this point (depending upon temperature). Dr. Goldberg tells me that when he sees the whey start to separate, he stops.
3. Greek Yogurt: Straining the WheyMore potentially good news for low-carbers: It turns out that most of the lactose in milk and yogurt is in the whey. It is easy to strain much of the whey out of yogurt yourself, or buy Greek-style yogurt. To strain the whey out of yogurt yourself, put a coffee filter in a strainer or colander and put that over a bowl in the refrigerator. It will become thicker and thicker as time goes on, so you can stop when it is the consistency you wan. Eventually it can reach the thickness of soft cream cheese, often called yogurt cheese. This can be eaten any way you want or mixed with other ingredients for foods such as dips. Another advantage to straining yogurt is that the concentrated yogurt has more protein per cup, as well as less carbohydrate.
Related Link: Carb Counts in Dairy Products