Net carbs are total carbohydrates minus fiber — the idea being that fiber passes through without being absorbed as glucose, so it should not count against you. A cup of black beans with 41 g of total carbs and 15 g of fiber has 26 g net. Some labels also subtract sugar alcohols, which is where the concept gets slippery.
The fiber subtraction is mostly legitimate: insoluble fiber is not absorbed, and soluble fiber has minimal direct glucose impact while actively slowing everything else down. The sugar-alcohol subtraction is where marketing outruns physiology — maltitol, common in sugar-free candy and bars, is absorbed enough to raise glucose in many people, sometimes at half the strength of regular sugar. Erythritol genuinely has near-zero impact. The label treats them the same; your glucose does not.
Where people land in practice:
- For whole foods (beans, vegetables, berries), net carbs track real-world response well.
- For processed low-carb products, trust your CGM over the front of the package.
- Whether you count total or net carbs for your own purposes is genuinely individual — people differ in which number matches their curves, and it is worth working out with your care team.
The concept is a useful lens, not a loophole. High-fiber foods earn the discount; sugar-free candy usually does not.
