Open a bag of erythritol and you would think you were looking at sugar: white crystals that taste sweet and dissolve in liquid. But if you looked at sugar alcohol under a microscope, you would see that its molecular structure is slightly different than sugar- rendering it less metabolizable by the body, and having less (or no) effect on blood glucose after eating them.
Despite the miracle-of-science sound of “xylitol” and “erythritol,” both of these sugar alcohols come from natural plant sources, such as birch trees and corn. The judicious use of sugar alcohols makes it possible to create low carb desserts that taste very close to the real thing. Many dieters using sugar alcohols subtract them from total carbohydrates, much like fiber. Boston Keto Kitchen uses erythritol in our ice cream and donuts, with delicious results.
It is not debated that erythritol has a glycemic index of zero, meaning it does not affect blood glucose (and presumably insulin) at all. But for reasons that are not clear yet, sugar alcohols do seem to lower ketone levels in some people.
This is likely why the Ketogenic Diet Center at Johns Hopkins, the premier center for the treatment of childhood epilepsy through this diet, advises parents to count each gram of sugar alcohol as a gram of regular carbohydrate. There needs to be more research into why this substance drops ketones in some people, but the clinical evidence points in that direction.