SCIENZA
Net carbs: how to work them out (and why total carbs mislead)
Published on September 4, 2026 · Updated on January 1, 1970
On keto what counts isn't total carbs but net carbs: total minus fibre. The formula, worked examples with avocado and chia seeds, and the European label trap that almost nobody explains.
You pick up a bag of chia seeds and read 42 g of carbs per 100 g. Your first thought is to put it back. Your second, if you know anything about keto, is that something doesn't add up: chia seeds are one of the most recommended foods on a ketogenic diet.
It doesn't add up because that 42 isn't the number that matters.
The formula
On keto you count net carbs:
Net carbs = total carbs − fibre
In chia seeds, 34.4 g of that 42 is fibre. That leaves 7.6 g net. From "avoid" to "go ahead", with nothing changing in the product itself — only the number you're looking at.
Why fibre doesn't count
Fibre is a carbohydrate your gut cannot digest. It isn't broken down into glucose, it doesn't enter your bloodstream, it doesn't raise blood sugar and it doesn't trigger insulin. It passes through and leaves.
That's why it gets subtracted: ketosis depends on how much glucose reaches your blood, and fibre brings none.
Three examples that change everything
| Food | Total | Fibre | Net |
|---|---|---|---|
| Avocado | 9 g | 6.8 g | 2.2 g |
| Chia seeds | 42 g | 34.4 g | 7.6 g |
| Almonds | 22 g | 12.5 g | 9.5 g |
Avocado is the starkest case: counted on total carbs it looks four times worse than it is. And along with eggs it's the emblem of the ketogenic diet.
The European label trap
Here's the part that confuses almost everyone, and it depends on where you are.
In the United States labels show Total Carbohydrate, and fibre is included in that figure. So you do need to subtract it.
In Europe, under EU regulation 1169/2011, the "carbohydrate" line means available carbohydrate only: fibre is already excluded and listed on its own separate line.
In practice:
- On an Italian, French or German label reading "carbohydrate 5 g — of which sugars 2 g — fibre 3 g", net carbs are 5 g, not 2.
- On a US table (or on USDA, the database most apps rely on) reading "carbohydrate 8 g, of which fibre 3 g", net carbs are 5 g.
Subtracting fibre from a European label means counting it twice, making a food look better than it is. It's the most common mistake people make when they move between an American app and a product bought at their local supermarket.
Rule of thumb: if fibre has its own line and is not preceded by "of which", it's most likely already outside the count.
What about polyols?
Polyols (erythritol, maltitol, xylitol — the ones in "sugar-free" products) are a third case. They're poorly absorbed and raise blood sugar far less than sugar does, so on keto they're subtracted in whole or in part:
Net = total − fibre − polyols
With one caveat: erythritol is essentially inert and can be subtracted in full, while maltitol does affect blood sugar, so counting at least half of it is the safer choice.
What to do with this
The daily limit on a standard ketogenic diet is 20-50 g of net carbs, not total. Across a day built on vegetables, nuts and seeds that difference can be 20-30 g: the difference between staying in ketosis and dropping out of it without understanding why.
On Deketox every food page shows net carbs as the headline number, with total and fibre underneath, so you can see where the subtraction comes from.
- Net carb calculator — pick a food, enter the grams, read the net carbs
- Food archive — 100 foods with a keto verdict
The information in this article is for general education and does not replace advice from a doctor or dietitian.