The Net Carbs Calculation: What It Is, How It Works, and Why It Matters
A companion explainer to There’s No Safety Net in Net Carbs
If you read our main piece on net carbs and wanted more detail on the science behind it, here’s exactly how the calculation works, which ingredients are doing the subtracting, and what the research says about each of them.
The formula many manufacturers use is straightforward on its surface: total carbohydrates, minus dietary fiber, minus sugar alcohols, equals net carbs. That logic is reasonable in theory. In practice, the details matter enormously.
The glycemic index: The glycemic index, or GI, measures how quickly a food raises blood sugar, with pure glucose set at 100 as the reference point and table sugar sitting at approximately 60. Not all sugar alcohols have the same glycemic index, and the difference between them is significant for anyone managing blood sugar.
Erythritol: Glycemic index of essentially zero. It’s absorbed in the small intestine and excreted unchanged, meaning it has minimal effect on blood sugar or insulin. Subtracting it from the carbohydrate count is often considered scientifically defensible.
Maltitol: Glycemic index of approximately 36 in powdered form and up to 52 as a syrup, far closer to table sugar than to erythritol. Maltitol brings a significantly higher glycemic index compared to other polyols, making it less suitable for people with diabetes than lower-GI or zero-GI options. Yet in the net carbs calculation, maltitol and erythritol are subtracted identically, as though their effect on blood sugar were the same.
Other sugar alcohols: Sorbitol has a glycemic index of approximately 9, xylitol approximately 13, and lactitol approximately 6. All are lower than maltitol but none are zero, meaning they all affect blood sugar to varying degrees that the net carbs calculation doesn’t distinguish between.
IMO fibers: Isomalto-oligosaccharides, commonly known as IMOs, were widely added to low-carb products as a fiber ingredient, allowing them to be subtracted in the net carbs calculation. Some research suggests IMOs may not behave like true fiber, and that their effect on blood sugar may be greater than the label implies. The science is still evolving, but their impact is less settled than the net carbs calculation makes it look.
The FDA’s 2016 action: When the agency revised the nutrition facts label in 2016, it defined dietary fiber so that only certain intrinsic or FDA-recognized added fibers with demonstrated physiological effects could be counted on the panel. This was a direct response to the widespread practice of adding inexpensive isolated fibers specifically to boost the fiber count. The action improved the Nutrition Facts panel, but it didn’t extend to the net carbs calculation, which remains largely unregulated.
The bottom line: Net carb claims are created by food brands for marketing purposes. The number is a calculation the manufacturer designed, using ingredients the manufacturer selected, and subtracted according to rules the manufacturer invented. Current FDA rules let manufacturers group sugar alcohols together on the nutrition facts panel, so even there the label may not tell you whether they used the kind that affects blood sugar, like maltitol, or the kind that barely registers, like erythritol. The one place maltitol can’t hide is the ingredient list, where it must be named. For anyone making decisions about blood sugar, or assuming a low net-carb number means low calorie, that list tells a more complete and more honest story than the front of the package ever will.
**************
MEDICAL ADVICE DISCLAIMER
DISCLAIMER: This website does not provide medical advice. For health or wellness-related content, SFD Media LLC emphasizes that information about medicines, treatments, and therapeutic goods (including text, graphics, and images) is provided for general information only. No material on this site is intended to substitute for professional medical advice, diagnosis, or treatment. Users are advised to independently evaluate and verify the accuracy, reliability, and suitability of the information before relying on it. You should not rely on the content as a substitute for professional medical advice. Consult with a physician or other health care professional for any health concerns or questions you may have. SFD Media LLC is not responsible for any action taken based on the information provided on this website. The use of any information provided on this website is solely at your own risk.
