The ketogenic diet is defined by extremely low carbohydrate intake, moderate protein, and high fat consumption. The primary goal is to shift the body’s metabolism into ketosis, where it burns fat for fuel instead of glucose. Maintaining the strict carbohydrate limit (often 20 to 50 grams per day) requires precise tracking of food intake. This tracking introduces the term “net carbs,” which is necessary for successfully maintaining ketosis.
Defining and Calculating Net Carbs
Net carbohydrates represent the portion of total carbohydrates that the body can digest and convert into glucose. The standard “Total Carbohydrates” listed on a nutrition label includes starches, sugars, dietary fiber, and sugar alcohols. Low-carb dieters use a calculation to determine their true carbohydrate load: Net Carbs = Total Carbohydrates – (Dietary Fiber + Sugar Alcohols). This subtraction is not a formal requirement for food labeling, but it determines the amount of carbohydrate that will influence blood sugar levels. This distinction is applied because not all carbohydrates have the same metabolic effect.
Why Net Carbs Align with Ketosis Goals
Counting net carbs is based on the physiological fact that certain carbohydrates are not absorbed into the bloodstream. Dietary fiber is a primary example because the human digestive system lacks the necessary enzymes to break it down. As a result, fiber passes through the small intestine intact, providing bulk without contributing to blood glucose. This lack of absorption prevents the release of insulin that normally occurs after eating digestible carbohydrates. Insulin regulates blood sugar and, when present, signals the body to stop producing ketones, so subtracting non-digestible carbohydrates allows dieters to consume foods with a higher total carbohydrate count without compromising ketosis.
The Complexities of Counting Non-Digestible Carbs
While subtracting dietary fiber is straightforward, including sugar alcohols (polyols) introduces complexities, as these sweeteners vary significantly in their impact on blood sugar. Some, such as erythritol, are absorbed but not metabolized, meaning they have a glycemic index of zero and can be subtracted entirely. However, others like maltitol and xylitol are partially absorbed and can cause a noticeable increase in blood glucose and insulin levels. Maltitol, for instance, has a glycemic index high enough (35 to 52) to potentially interfere with ketosis, leading many to recommend counting about 50% of its grams as net carbs. Reading ingredient lists is important because a product’s “net carb” claim may not align with an individual’s unique metabolic response.