"Net carbs" shows up constantly on low-carb and keto-marketed products, usually printed more prominently than the "Total Carbohydrate" line required by law. The two numbers are trying to answer related but different questions, and only one of them is actually regulated.

What total carbs includes

"Total Carbohydrate" on a U.S. Nutrition Facts label is a required, standardized figure: it includes all carbohydrate in the food, whether it is starch, natural or added sugar, or fiber, all added together. This is the number that reflects the full carbohydrate content of the product as manufactured, with no adjustments.

What net carbs is trying to measure

"Net carbs" is a marketing calculation, typically total carbohydrate minus fiber and, on many products, minus sugar alcohols as well. The idea behind it is that fiber and most sugar alcohols have a smaller effect on blood sugar than other carbohydrates, so subtracting them gives a number closer to the carbohydrate that actually raises blood glucose. The logic has some basis in how these components are digested, but the resulting number is calculated differently by different manufacturers.

Why net carbs is not a regulated term

Unlike "Total Carbohydrate," the FDA does not define or require a standardized "net carbs" calculation, which means two products can both print a "net carbs" number arrived at using different assumptions about how much a given sugar alcohol actually affects blood sugar. Some sugar alcohols, like maltitol, have a more significant blood sugar effect than the "subtract it entirely" approach assumes, which means a product's net carbs number can meaningfully understate its real effect for some people.

Fiber and sugar alcohols: the two common subtractions

  • Fiber: generally has minimal effect on blood sugar for most people and is a reasonably safe subtraction, though very high fiber counts on some products are worth a second look for plausibility.
  • Sugar alcohols like erythritol: tend to have a small blood sugar effect for most people, making the subtraction reasonably fair.
  • Sugar alcohols like maltitol: have a more noticeable blood sugar effect than erythritol despite being treated similarly in many net carbs calculations, a common source of the gap between a product's marketed net carbs and how it actually behaves for some people.

The glycemic index connection

The idea behind subtracting fiber and sugar alcohols from a carb count is loosely tied to the concept of glycemic index, a measure of how much a given food raises blood sugar relative to pure glucose. Fiber generally has a low glycemic impact because it isn't broken down into glucose the way starch is, which is the legitimate part of the net-carbs logic. Where the logic breaks down is in treating every subtracted ingredient as equally low-impact, when in practice glycemic effects vary meaningfully within both the fiber and sugar-alcohol categories.

What to actually rely on

For most people managing blood sugar, the Total Carbohydrate line, combined with a look at the ingredient list to see which specific fiber or sugar alcohol is being subtracted, tends to be a more reliable starting point than trusting a "net carbs" number at face value. If a particular sugar alcohol seems to affect you more than a product's net carbs claim would suggest, that is a reasonable, individual signal worth paying attention to over the marketed number, and it is a good detail to bring up with a doctor or dietitian if you are working closely with them on blood sugar management.

A quick example

A protein bar might list 22 grams of Total Carbohydrate, 9 grams of fiber, and 8 grams of maltitol, arriving at a marketed "5g net carbs." The Total Carbohydrate figure of 22 grams is the regulated, verifiable number. The "5g net carbs" figure assumes both the fiber and the maltitol have close to zero blood sugar effect — a reasonably fair assumption for the fiber, but a more questionable one for the maltitol given its documented glycemic effect, which means the real-world blood sugar impact of that bar likely sits somewhere between the two printed numbers rather than at either one.

A useful habit for anyone eating a lot of "net carbs"-labeled products is keeping a personal note of how specific products actually affect you, whether through a glucose monitor or simply how you feel afterward, rather than assuming the marketed number is the final word. Two "5g net carbs" bars from different brands can behave quite differently in practice if one leans on erythritol and the other leans on maltitol for its sweetness, even though the front-of-package number looks identical on both.

None of this means net carbs marketing is dishonest in a legal sense — it's simply an unregulated calculation layered on top of a regulated one, and the gap between the two is exactly where it pays to look a little closer, particularly for anyone managing blood sugar as a daily, ongoing concern rather than an occasional consideration.