Net carbs represent the carbohydrates in a food that your body actually digests and converts into blood sugar. The basic formula is simple: take the total carbohydrates listed on a nutrition label, then subtract the fiber and any sugar alcohols. What’s left is the net carb count. A protein bar with 25 grams of total carbs, 10 grams of fiber, and 5 grams of sugar alcohols would have 10 grams of net carbs.
Why Fiber and Sugar Alcohols Don’t Count
Fiber is the structural part of plants, found in vegetables, fruits, grains, nuts, and legumes. Your body cannot digest or absorb it. Fiber passes through your digestive system largely intact, which means it doesn’t raise your blood sugar or provide glucose for energy. Even though fiber is technically a carbohydrate and shows up under “Total Carbohydrates” on a nutrition label, it behaves nothing like bread or sugar once you eat it.
Sugar alcohols are a different story. They’re sweeteners commonly found in “sugar-free” or “low-carb” packaged foods, and most of them have very little impact on blood sugar compared to regular sugar. For context, table sugar has a glycemic index of 65. Erythritol, the most popular sugar alcohol in low-carb products, has a glycemic index of just 1. Xylitol comes in at 12, sorbitol at 4, and mannitol at 2. The outlier is maltitol, which scores 35 on the glycemic index. That’s still lower than table sugar, but it’s high enough that counting it as zero net carbs is misleading.
The Formula Isn’t Perfect
The American Diabetes Association notes that the net carb equation “is not entirely accurate because the contribution of fiber and sugar alcohols to total carbohydrates depends on the types present.” In other words, not all fiber behaves identically, and not all sugar alcohols are created equal. Subtracting 10 grams of erythritol is reasonable since it barely touches your blood sugar. Subtracting 10 grams of maltitol is more generous than reality warrants.
Some people adjust for this by only subtracting half the grams of sugar alcohols (excluding erythritol, which they subtract fully). There’s no official standard for this. It’s a judgment call, and how much it matters depends on how tightly you’re tracking your carb intake.
Net Carbs Have No Official Regulation
The term “net carbs” has no legal definition from the FDA. Food manufacturers can put it on packaging, but there’s no standardized rule governing how it’s calculated. The numbers you see on the front of a protein bar or snack wrapper are the company’s own math. The Nutrition Facts panel on the back, which lists total carbohydrates, fiber, and sugars separately, is the regulated part. That’s the information you’d use to calculate net carbs yourself.
This lack of regulation means two brands could calculate net carbs differently for similar products. One might subtract all sugar alcohols completely; another might not. If net carbs matter to you, it’s worth doing the subtraction yourself from the Nutrition Facts panel rather than trusting a marketing claim on the front of the package.
Where Allulose Fits In
Allulose is a newer sweetener showing up in low-carb foods, and it creates a confusing label situation. It’s technically a sugar (a monosaccharide), so it must be included in “Total Carbohydrates” on the Nutrition Facts panel. But your body barely uses it. About 70% of the allulose you eat is eliminated intact through urine and feces within 48 hours. It produces only a negligible increase in blood sugar and insulin, and it delivers no more than 0.4 calories per gram (compared to 4 calories per gram for regular sugar).
The FDA currently allows manufacturers to exclude allulose from “Total Sugars” and “Added Sugars” on labels, but it still appears in the total carbohydrate line. So if you’re calculating net carbs from a product sweetened with allulose, you’d subtract it along with fiber and sugar alcohols. Many brands note this on the label, but not all do.
Net Carbs in Whole Foods
Net carbs aren’t just relevant for packaged low-carb products. They’re useful for understanding how whole foods affect your blood sugar too. High-fiber foods can have significantly lower net carbs than their total carb counts suggest.
A cup of cooked lentils has about 40 grams of total carbs but 15.5 grams of fiber, bringing the net carbs down to roughly 24.5 grams. A cup of black beans has around 41 grams of total carbs and 15 grams of fiber, landing at about 26 net carbs. A cup of raspberries contains about 15 grams of total carbs and 8 grams of fiber, so only about 7 net carbs. A cup of boiled broccoli has roughly 11 grams of total carbs and 5 grams of fiber, yielding about 6 net carbs.
Compare that to foods with little fiber. A medium banana has about 27 grams of total carbs but only 3 grams of fiber, so roughly 24 net carbs. White rice and white bread have very little fiber, meaning their net carbs are nearly identical to their total carbs.
Why People Track Net Carbs
Net carb counting is most popular among people following ketogenic or other low-carb diets, where the goal is to keep carbohydrate intake low enough that the body shifts to burning fat for fuel. A typical keto target is 20 to 50 net carbs per day. Using net carbs instead of total carbs allows more room for vegetables, nuts, and seeds without “spending” carb allowance on fiber your body won’t absorb anyway.
People managing diabetes also find the concept useful because net carbs more closely predict how much a food will actually raise blood sugar. That said, the American Diabetes Association cautions that the calculation has limitations, especially with sugar alcohols. If you’re using insulin or medication that requires precise carb counting, the imprecision of net carb math matters more.
A Note on Sugar Alcohols and Digestion
Because your body can’t fully digest sugar alcohols, eating too many can cause bloating, gas, and diarrhea. Research suggests that 10 to 15 grams per day is generally well tolerated, but amounts above that often trigger digestive discomfort, sometimes within hours of eating. If you’re eating multiple low-carb bars or sugar-free candies in a day, the sugar alcohols can add up quickly. Erythritol tends to be the best tolerated, while sorbitol and maltitol are more likely to cause problems at lower amounts.