Yogurt and Low Carb Diets

January 10, 2011 10:16 AM

I just read a webpage indicating that due to the way the govt makes food mfgrs calulate ingredients in their products, the amount of carbs in yogurt is overstated. Much of the lactose in the milk used to make it is converted to lactic acid, but remains in the carb count in the nutrition facts on the carton. I understood the fermentation process before, but was not aware of the label being misleading. Could anyone point me to research or a definitive source showing that this is true? Thanks.
posted by ackptui to Food & Drink (1 answer total)

21CFR101.9 governs nutritional labelling of foods. Specifically, from paragraph (c)(6):

(6) "Carbohydrate, total'' or "Total carbohydrate'': A statement of the number of grams of total carbohydrate in a serving expressed to the nearest gram, except that if a serving contains less than 1 gram, the statement "Contains less than 1 gram'' or "less than 1 gram'' may be used as an alternative, or if the serving contains less than 0.5 gram, the content may be expressed as zero. Total carbohydrate content shall be calculated by subtraction of the sum of the crude protein, total fat, moisture, and ash from the total weight of the food. This calculation method is described in A. L. Merrill and B. K. Watt, "Energy Value of Foods--Basis and Derivation,'' USDA Handbook 74 (slightly revised 1973) pp. 2 and 3, which is incorporated by reference in accordance with 5 U.S.C. 552(a) and 1 CFR part 51 (the availability of this incorporation by reference is given in paragraph (c)(1)(i)(A) of this section). [emph. mine]

Going to the cited reference, we read:

The difference between 100 and the sum of the crude protein and fat, moisture, and ash is called the "total carbohydrate" or "carbohydrate by difference," a practice used by Atwater in his food tables and continued in this country. In addition to the true carbohydrates, this "difference" fraction may include such compounds as organic acids

So yes, it seems that lactic acid may be included among the "carbohydrate" value in labelling.

However! That's not the end of the story. First, even in yogurt, only a fairly small amount of lactose is converted to lactic acid. This article [full version may be behind paywall] found about 0.7-0.8 g lactic acid per 100g of yogurt; This page says 0.7-1.2 g lactic acid per 1 dL yogurt. These both work out to somewhere around 2g per an 8 fl. oz. serving. Meanwhile, this page reports nutritional data of 19g carbohydrates per 8 fl. oz. plain yogurt, so you're looking at a maybe 10% difference. It may be overstated, but not by that much.

Further, it's unclear to me whether ingested lactic acid might be used as an energy source by the body anyway. Certainly, lactic acid in the blood can be used as an energy source, and it seems that ingested lactate may be used as an energy source as well, so it's possible that even though it's not technically a carbohydrate, lactic acid might to some extent function as one nutritionally.
posted by DevilsAdvocate at 2:30 PM on January 10, 2011 [3 favorites]