Net carbs are the carbohydrates in a food that your body actually digests and converts into blood sugar. You calculate them by taking the total carbohydrates listed on a nutrition label and subtracting fiber and sugar alcohols. If a protein bar has 25 grams of total carbs, 10 grams of fiber, and 5 grams of sugar alcohols, the net carbs would be 10 grams.
Why Some Carbs Don’t Count
The logic behind net carbs is straightforward: not every carbohydrate you eat behaves the same way once it hits your digestive system. Fiber is technically a carbohydrate, but your body can’t break it down. Instead of being absorbed and raising blood sugar, fiber passes through your stomach and intestines largely intact. Soluble fiber dissolves in water and forms a gel-like substance that slows digestion, which actually helps stabilize blood sugar rather than spiking it. Insoluble fiber doesn’t dissolve at all and moves through your system whole, helping with regularity and improving insulin sensitivity.
Sugar alcohols (found in many “sugar-free” products) follow a similar principle, though not as cleanly. They’re partially absorbed, meaning they raise blood sugar far less than regular sugar does. Most sugar alcohols have a glycemic index in the single digits, compared to table sugar’s score of 65. Erythritol scores just 1, sorbitol lands at 4, and xylitol comes in at 12. Because their impact on blood sugar is so small, they’re subtracted from total carbs in net carb calculations.
The Basic Formula
For most foods, the math looks like this:
Net carbs = Total carbohydrates − Fiber − Sugar alcohols
Both fiber and sugar alcohols are listed separately on U.S. nutrition labels underneath total carbohydrates, so you already have the numbers you need. For whole foods like vegetables, fruits, and legumes that don’t have sugar alcohols, you’re simply subtracting fiber from total carbs.
Not All Sugar Alcohols Are Equal
Here’s where net carb math gets less reliable. While erythritol barely registers on the blood sugar scale, maltitol has a glycemic index of 35 and is about 75% as sweet as sugar. That’s dramatically higher than other sugar alcohols. Subtracting 100% of maltitol from your carb count overstates the benefit, because maltitol does cause a modest blood sugar rise.
Some people who track carbs closely subtract only half the grams from sugar alcohols like maltitol and xylitol, while subtracting erythritol entirely. There’s no official standard for this, which is part of the problem with net carbs as a concept. A “3 net carbs” claim on a candy bar sweetened with maltitol is less meaningful than the same claim on a bar sweetened with erythritol.
Where Allulose Fits In
Allulose is a newer sweetener showing up in low-carb products. It’s technically a sugar (a rare sugar found naturally in small amounts in figs and raisins), but your body absorbs very little of it. The FDA has signaled that manufacturers can exclude allulose from both the “Total Sugars” and “Added Sugars” lines on nutrition labels, and the agency counts it as only 0.4 calories per gram instead of the 4 calories per gram that regular sugar carries. If a product contains allulose, it’s typically already excluded from the sugar count on the label, and most people subtract it from their net carb calculations as well.
The FDA Doesn’t Recognize “Net Carbs”
One important detail: “net carbs” is not an official term. The FDA has never defined it, and the American Diabetes Association doesn’t recommend using it. Food companies can put “net carbs” on their packaging, but there’s no regulated standard behind the number. Two different brands could calculate net carbs differently and both be technically allowed to print their figure on the label.
This matters because it means you can’t always take a “net carbs” claim at face value. Some companies subtract all sugar alcohols entirely, others subtract a portion, and some may include or exclude allulose differently. Reading the full nutrition label and doing your own subtraction gives you more control over the number you’re working with.
Who Benefits From Counting Net Carbs
Net carbs are most useful for people following low-carb or ketogenic diets, where staying under a daily carbohydrate threshold (often 20 to 50 grams) is central to the approach. By subtracting fiber, you avoid penalizing yourself for eating vegetables, avocados, nuts, and other high-fiber foods that don’t actually raise blood sugar. A cup of broccoli has about 6 grams of total carbs but only around 3.5 net carbs after subtracting fiber, which makes a real difference when your daily budget is tight.
People managing diabetes also find net carbs helpful for estimating how food will affect their blood sugar, though the American Diabetes Association recommends focusing on total carbohydrates and working with a care team to fine-tune from there.
Watch for Digestive Side Effects
Foods marketed as low in net carbs often compensate with large amounts of fiber or sugar alcohols to keep the number down. This can cause real digestive discomfort. The average adult tolerates roughly 20 to 50 grams of sugar alcohols per day before experiencing bloating, gas, or diarrhea. People with irritable bowel syndrome hit that threshold much sooner. If a protein bar has 15 grams of sugar alcohols and you eat two or three in a day, you may be well into uncomfortable territory. The low net carb count on the label won’t tell you that.
Erythritol tends to be the best tolerated because most of it is absorbed in the small intestine and excreted without reaching the large intestine where fermentation causes gas. Sorbitol and maltitol are more likely to trigger symptoms at lower doses.