How to Read a Nutrition Label for Blood Sugar
Which numbers on a nutrition label actually matter for blood sugar, in what order — and why "net carbs" is the one to be sceptical of.
Most label advice tells you to look at everything. Here's the short version: four numbers, in order.
1. Total carbohydrate
Not sugar. Not net carbs. Total carbohydrate is the number that matters most, because starch becomes glucose just as surely as sugar does.
A cracker with zero grams of sugar and twenty grams of carbohydrate is still twenty grams of carbohydrate.
2. Fiber
Fiber is carbohydrate your body largely doesn't absorb, and it slows everything else down. More is better. Three grams or more per serving is a reasonable bar for a bread or cereal.
3. Protein
Not a blood sugar number directly, but it tells you whether this food will hold you. It also tells you whether you're anywhere near the 25 to 30 grams per meal that matters after fifty.
4. Added sugars
Separate from total sugars, which include those occurring naturally in fruit and dairy. Added sugars are the ones worth minimizing, and they appear under a great many names — anything ending in "-ose," plus syrups, malt, molasses, concentrates and nectars.
The serving size trap
Check it before anything else. A packet may contain two or three servings, and the numbers on the panel refer to one. It's the most common way a label misleads without technically lying.
On "net carbs"
Net carbs means total carbohydrate minus fiber and sugar alcohols. It's not a regulated term, and the arithmetic is only sometimes valid.
Subtracting fiber is reasonable. Subtracting erythritol is reasonable — it passes through largely unabsorbed. Subtracting maltitol is not: it's partially absorbed and contributes directly to blood glucose, so a "2g net carb" bar sweetened with maltitol will do considerably more than 2g suggests.
Treat net carbs on packaging as marketing rather than measurement.
The ingredient list tells you more than the panel
Ingredients are listed by weight. If a sweetener or refined flour appears in the first three, that's most of what you're eating, whatever the front says.
A short ingredient list is generally a good sign. A long one usually means processing has done work that your digestion would otherwise have done.
Try this week: turn over three products you buy regularly and find total carbohydrate and serving size. Nothing else. It's a five-minute habit that changes your shopping permanently.
Education, not medical advice.
Sources
- Atkinson FS, et al. International tables of glycemic index and glycemic load values 2021. *Am J Clin Nutr* 2021;114(5):1625–1632 View source