Two people can both say they eat twenty grams of carbs a day on keto and mean quite different things, because one is counting total carbohydrate and the other is counting net carbs. Knowing the difference, and which to follow, saves a lot of confusion.
The basic idea
Net carbs are the carbohydrates that actually raise your blood sugar and so matter for ketosis. You arrive at them by taking the total carbohydrate in a food and subtracting the parts your body does not absorb as usable sugar, chiefly fibre and most sugar alcohols. Total carbs, by contrast, is simply the whole figure before any subtraction.
The logic is that fibre passes through largely undigested and sugar alcohols like erythritol are mostly not metabolised, so neither does much to your blood sugar. Counting net carbs lets you eat more leafy veg, nuts and seeds, which are high in fibre, without those grams eating into your daily limit.
Working it out from a label
On a British or American label you take the total carbohydrate and subtract the grams of fibre, and any sugar alcohols if listed, to get net carbs. On a European label, including Belgian ones, there is a twist worth knowing: the “glucides” or “koolhydraten” figure already excludes fibre, which is listed separately as “fibres” or “vezels”. So the carbohydrate number on a Belgian label is effectively already closer to net carbs, and you do not subtract fibre again. There is more on European labels in the reading food labels piece.
Net or total: which to count
Most people do perfectly well counting net carbs, and it makes the diet more pleasant and sustainable. A minority, particularly those who are very insulin resistant or who stall easily, find they get better results counting total carbs, which is simply stricter. If net carbs are working for you, there is no reason to switch. If you are doing everything right and not progressing, tightening to total carbs is one lever to try.
Where people trip up
The catch is processed “keto” and “low carb” products that lean heavily on the net carb claim. A bar marked “two grams net carbs” may contain a pile of sugar alcohols, and some of those, maltitol in particular, do raise blood sugar more than the marketing implies. Whole foods rarely cause this problem, because their fibre is genuine. Treat dramatic net carb claims on packaged products with a little suspicion, and let real food do most of the work.
This is general information about the ketogenic diet, not medical advice. Keto does not suit everyone; if you are pregnant, on medication, or managing a condition such as diabetes, speak to a doctor or dietitian first.