Net carbohydrates are the carbs in a food that your body actually digests and converts to blood sugar. You calculate them by taking the total carbohydrates listed on a nutrition label and subtracting fiber and sugar alcohols. The idea is simple: since fiber and certain sugar substitutes pass through your body without raising blood sugar the way starches and sugars do, they shouldn’t “count” toward your carb intake. But the concept is more nuanced than that formula suggests, and it has no official regulatory definition.
The Basic Formula
Net carbs = total carbohydrates − fiber − sugar alcohols. If a protein bar lists 25 grams of total carbohydrates, 10 grams of fiber, and 5 grams of sugar alcohols, its net carb count would be 10 grams. That number is meant to represent the portion that will meaningfully affect your blood sugar.
This calculation became popular through low-carb and ketogenic diets, where people track net carbs to stay under a daily threshold (often 20 to 50 grams). Many food companies now print net carb counts on their packaging. The problem is that neither the FDA nor the American Diabetes Association recognizes “net carbs” as an official term. The FDA recommends using total carbohydrates on the nutrition facts label, and there is no legal standard for how companies must calculate or display net carbs.
Why Fiber Gets Subtracted
Fiber is technically a carbohydrate, but your body doesn’t break it down the way it breaks down starch or sugar. Instead of being absorbed in the small intestine and entering your bloodstream as glucose, fiber passes through your digestive system largely intact. The CDC notes that fiber doesn’t cause a spike in blood sugar the way other carbohydrates can. It also moves slowly through the stomach, which is why high-fiber foods tend to keep you feeling full longer.
This is why subtracting fiber from total carbs makes physiological sense. If you eat a cup of broccoli with 6 grams of total carbohydrates and 2.4 grams of fiber, only about 3.6 grams are the kind your body converts to glucose. For most whole foods, the net carb calculation works reasonably well for this reason.
Why Sugar Alcohols Are Trickier
Sugar alcohols are sweeteners found in many “sugar-free” and “low-carb” products. Common ones include erythritol, xylitol, sorbitol, and maltitol. The standard net carb formula subtracts all of them equally, but your body absorbs each one differently.
Erythritol is barely absorbed at all, contributing almost no calories or blood sugar impact. Maltitol, on the other hand, is partially absorbed in the small intestine at rates ranging from 5% to 80%, depending on the individual and the amount consumed. That means a “low net carb” bar sweetened with maltitol can still raise your blood sugar noticeably. Subtracting 100% of maltitol from total carbs overstates how “free” those carbs really are.
A more conservative approach that some people use is to subtract only half of the sugar alcohols (except erythritol, which can be fully subtracted). This isn’t an official guideline, but it better reflects the partial absorption of sweeteners like maltitol, sorbitol, and xylitol.
Where Allulose Fits In
Allulose is a newer sweetener showing up in low-carb products. It’s chemically a sugar, so the FDA requires it to be included in the total carbohydrate count on nutrition labels. However, the FDA allows manufacturers to exclude allulose from the “Total Sugars” and “Added Sugars” lines, because it provides only about 0.4 calories per gram (compared to 4 calories per gram for regular sugar) and has minimal effect on blood sugar.
This creates a confusing label situation. A product sweetened with allulose may show a high total carbohydrate number, but much of that comes from a sweetener your body barely uses for energy. Most people following a net carb approach subtract allulose entirely, similar to erythritol. If you see a surprisingly high total carb number on a product marketed as low-carb, check the ingredients for allulose.
When Net Carbs Work Well
For whole, minimally processed foods, net carbs give you a useful picture of how much digestible carbohydrate you’re eating. Vegetables, nuts, seeds, and legumes all contain significant fiber, and subtracting that fiber reflects the real metabolic impact of those foods. An avocado with 12 grams of total carbs and 10 grams of fiber genuinely behaves like a 2-gram-carb food in your body.
Net carbs also work well as a general framework if you’re following a low-carb diet and eating mostly real food. The formula’s weaknesses show up mainly with processed products that use large amounts of sugar alcohols or novel sweeteners to engineer a low net carb count on the label.
When the Formula Falls Short
The core assumption behind net carbs is that fiber and sugar alcohols are not absorbed or metabolized. As the American Diabetes Association points out, this is not always true. Some fibers and sugar alcohols are partially digested, still provide calories, and still affect blood glucose.
This matters most in two situations. First, packaged foods with high amounts of sugar alcohols (especially maltitol) may raise your blood sugar more than their net carb count suggests. If you’re managing diabetes or closely monitoring ketosis, this gap between the label and your actual response can be significant. Second, different people metabolize these compounds differently. Your gut bacteria, the speed of your digestion, and even what else you ate in the same meal can change how much of a sugar alcohol gets absorbed.
For people with diabetes, both the FDA and the American Diabetes Association recommend using total carbohydrates rather than net carbs for meal planning and any insulin calculations. Total carbs give you a more conservative, predictable number to work with.
How to Read Labels With Net Carbs in Mind
Start with the “Total Carbohydrate” line on the nutrition facts panel. Directly beneath it, you’ll see fiber and sometimes sugar alcohols listed as sub-items. To calculate net carbs, subtract the full fiber amount and all or half of the sugar alcohols, depending on the type.
- Erythritol and allulose: subtract fully, as these have negligible blood sugar impact
- Maltitol, sorbitol, xylitol: subtract half to account for partial absorption
- Fiber: subtract fully from total carbohydrates
If a product’s front label claims a net carb number, flip to the nutrition facts and check the math yourself. Some companies use creative accounting, and since there’s no regulated definition, the number on the front of the package may not match what your body actually experiences. The ingredient list will tell you which specific sweeteners are used, which helps you decide how much to subtract.