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{{Skeleton}}Introduction/Summary.* Not all the carbs we eat can be digested, so net carbs is total carbohydrate minus the indigestible carbs are equally available; some do not produce glucose.* The simplest and most common adjustment is to subtract the amount of [[Fiber]] is partly digestedfrom the total carbohydrate intake, producing Short Chain Fatty Acids* The idea of Net Carbohydrates varies but the adjustments vary by diet. * Generally[[Fiber]] is not directly digested, so most [[Low Carbohydrate Diets]] define net carbohydrates as total carbohydrate less fiber ignore Fiber in calculating Net Carbohydrates. * The Atkins does not include Diet subtracts sugar alcohols in from net carbs* carbohydrates, but [[Ketogenic Diet]]s generally do not. Sugar alcohols such as Xylitol are likely to impact ketosis and should probably be considered 50-90% of the impact of a carbohydrate. See below for details. =Fiber=Fiber is almost universally ignored in calculating Net Carbs and has a sound physiological basis; Fiber does not provide the body with any carbohydrate. Some Fiber is converted by bacteria to Short Chain Fatty Acids (SCFA) which are then digested. However these SCFA provide some Calories but they don't provide any carbohydrate intake. Not only is Fiber subtracted from Net Carbs, the common recommendation is to try to keep your Fiber intake high as [[Health Risks of the Ketogenic Diet| constipation is a common side effect of the Ketogenic Diet]]. ==Non-Calorific Artificial Sweeteners==There is little evidence that artificial sweeteners cause an increase insulin production. In rats, artificial sweeteners with a bitter aftertaste, including saccharin, sodium cyclamate (banded in the US, marketed as Sweat N Low in Canada), stevia, and acesulfame-K (marketed as Sunett and Sweet One) increased insulin in isolated rat livers, but Aspartame did not<ref name="MalaisseVanonderbergen1998"/>. However, human studies do not show a similar result. A study on sucralose on humans showed no insulin response<ref name="Ma-2009"/>, and a study of a diet soda drink containing sucralose and acesulfame-K did not change the insulin response to subsequent glucose intake<ref name="Brown-2009"/>. ==Xylitol and Other Sugar Alcohol Sweeteners =Xylitol is a sugar alcohol sweetener that is often recommended for those on a ketogenic diet<ref name="Phinney-444"/>. Sugar alcohols are types of sugars that are not absorbed in the stomach, but are meet one of three fates<ref name="OkuNakamura2002"/>:* They are A portion is absorbed in the small intestine. Some sugar alcohols, like Xylitol are then metabolized, where others, such as arabitol and mannitol are excreted in the urine<ref name="Livesey-1992"/>.* Pass Another portion pass through the small intestine to be fermented by bacteria like [[Fiber]] to Short Chain Fatty Acids. * Excreted The remainder are excreted intact. Because of this excretion, large amounts of Xylitol can produce diarrhea at levels over 0.37 g/kg for males and 0.42 g/kg for females<ref name="Oku-2007"/>, so don't take too much at a time. If the Xylitol or other calorific sugar alcohols are absorbed in the small intestine they have a Calorie value similar to carbohydrate of around 4 Calories/gram, but if they are fermented by bacteria then they will provide around 2.5 Calories/gram. This is likely to explain the various estimates for the calories from Xylitol. (Estimates of 2.4-3 Calories/gram are commonly used for Xylitol<ref name="OkuNakamura2002"/>.) ==Responses to Xylitol==When 25g of Xylitol is consumed as a drink in a fasted state, Xylitol has been shown to have a number of effects on healthy men<ref name="Natah-1997"/>:* Find research Xylitol only raises blood glucose slightly and has a [[Glycemic Index]] of only 7. This suggests a small portion of Xylitol is converted to Glucose. * Xylitol does produce a rise in insulin though only about 20-25% of the rise that would be produced by the equivalent amount of glucose.* Unlike Glucose, Xylitol slightly reduces carbohydrate metabolism and slightly increases fat metabolism. * Xylitol helps prevent tooth decay be inhibiting the harmful bacteria in the mouth<ref name="Lynch-2003"/>. Xylitol also has some broader antibiotic effects<ref name="RenkoValkonen2008"/>, but it's not clear if this would have a negative impact on antidigestive bacteria. ==Sugar Alcohols and Ketosis==Xylitol has been shown to inhibit ketosis in isolated rat livers in a similar fashion to lactate<ref name="Woods-1973"/>, but this does not necessarily mean it will have a similar effect on humans that eat foods containing Xylitol. I would speculate that if a sugar alcohol like Xylitol is absorbed in the small intestine it is in the form of a carbohydrate, but fermentation by bacteria to Short Chain Fatty acids will not act as a carbohydrate. It is not clear to me under what circumstances sugar alcohols are absorbed in the small intestine rather than getting digested by bacteria. One analysis indicates that more than 50% of Xylitol is absorbed by the small intestine<ref name="Livesey-1992"/>. While the Atkins diet does not consider sugar alcohols as carbohydrates<ref name="WestmanPhinney2010"/>, a guide to ketogenic effect diets for epileptic patients does count sugar alcohols<ref name="Rubenstein2011"/>. My personal interpretation is that 50-90% of Sorbitol sugar alcohols such as Xylitol should be considered carbohydrates when evaluating a ketogenic diet.