Nutrition glossary
Net carbs: what they are and how to count them
Net carbs are the carbohydrates your body actually digests and absorbs. You work them out by taking the total carbohydrate on a label and subtracting the fibre, and sometimes some or all of the sugar alcohols.
The net carbs formula
Fibre is a carbohydrate, but your gut can't break it down into sugar, so it passes through without raising your blood sugar much. That is the whole idea behind net carbs. People on keto and other low-carb diets count them because fibre-rich foods like vegetables, nuts and seeds would otherwise "use up" the daily carb budget.
Net carbs = total carbohydrate − fibre − sugar alcohols (where relevant)
Keto plans usually aim for somewhere under about 20 to 50 g of carbohydrate a day, and many of them count that as net carbs.
A worked label example
Say you pick up a low-carb tortilla in a US shop. The Nutrition Facts panel lists, per wrap:
| Label line | Amount | What you do |
|---|---|---|
| Total Carbohydrate | 19 g | Start here |
| Dietary Fiber | 11 g | Subtract |
| Total Sugars | 1 g | Already inside the 19 g, so ignore |
| Net carbs | 8 g | 19 − 11 = 8 |
The same maths works for whole foods. Half a medium avocado has roughly 9 g of total carbohydrate, and about 7 g of that is fibre, so it comes to around 2 g net. A cup of cooked white rice has almost no fibre, so its total and net carbs are nearly the same, around 45 g.
US labels vs UK and EU labels
This catches a lot of people out. On US and Canadian labels, "Total Carbohydrate" includes fibre, so you subtract it. On UK and EU labels, the "Carbohydrate" line already leaves fibre out, and fibre is listed separately underneath.
So on a UK or EU pack, the carbohydrate figure is already close to net carbs. If you subtract the fibre again, you will undercount. A slice of wholemeal bread in the UK might show about 15 g carbohydrate and 3 g fibre; the net carbs are about 15 g, not 12 g. Australian labels follow a similar approach to the UK, so check which system a pack uses before you do the sum.
The sugar alcohol caveat
Sugar alcohols are sweeteners whose names often end in "-itol," such as erythritol, xylitol, sorbitol and maltitol. You'll find them in "keto" bars, sugar-free sweets and chocolate. They are only partly absorbed, but they are not all the same:
- Erythritol is barely absorbed, so most people subtract all of it.
- Maltitol is absorbed much more and can raise blood sugar noticeably. A common approach is to subtract only half.
- Large amounts of most sugar alcohols can cause bloating and diarrhoea.
Here's where brands differ. A bar with 23 g total carbs, 12 g fibre and 9 g maltitol might be marketed as "2 g net carbs." Counting half the maltitol gives you closer to 6 or 7 g.
Net carbs are not an official number
The US Food and Drug Administration does not define or regulate "net carbs," and it is not part of the Nutrition Facts panel. Any net carb figure on the front of a pack is the company's own sum, and companies don't all use the same method. When in doubt, ignore the front and do the calculation yourself from the panel on the back.
Net carbs also say nothing about the rest of the food. A processed keto cookie and a bowl of broccoli can have the same net carbs and very different value for your health. If you have diabetes and use insulin, don't change how you dose based on net carbs without talking to your diabetes team.
Common questions
How do you calculate net carbs?
Take the total carbohydrate on a US-style label, subtract the dietary fibre, and subtract sugar alcohols if the food has them (all of the erythritol, about half of most others). On a UK or EU label the carbohydrate figure already excludes fibre, so don't subtract it again.
Should I count net carbs or total carbs?
Most keto and low-carb plans use net carbs, because it lets you eat more vegetables, nuts and seeds. Some people with diabetes find total carbs easier and more predictable. Pick one method and stick with it so your numbers mean something.
How many net carbs a day is keto?
Most keto plans set a limit of around 20 to 50 g a day. Many people start at about 20 g, because that makes it more likely you'll reach ketosis.
Related
Learn how carbs affect blood sugar in the glycemic index entry, what cutting carbs does to your body in ketosis and electrolytes, and how carbs fit with protein and fat under macronutrients. For full plans, see the keto diet guide and low-carb diets.