What are Net Carbs? The role of fibre in a low-carb / ketogenic diet..

Fibre is a wonderful thing! Not only does it ensure that the food we eat ‘keeps moving’ through the digestive-system; it can actually help lower cholesterol and aids the prevention of a whole host of nasties… (NHS states heart disease, diabetes, some cancers &tc).

Whilst I can’t comment on the ‘preventative’ health-qualities of fibre; I can tell you a little bit about it, and why it’s so important to the ketogenic-dieter or diabetic.

People are often surprised to learn that fibre is actually a form of carbohydrate (alarms bells ring for all low-carb readers everywhere!!!). Having said this; it comprises the parts of plants which we cannot digest and is therefore not absorbed by the body. As such; it’s not a nutrient and contains no calories or vitamins.

Examples of indigestible plant-fibres include cellulose (the plant’s cell-walls), lignin (derived from the Latin word for wood & the thing which makes vegetables crunchy); and suberin (a waxy, rubbery material which is water-resistant, therefore acting as a barrier to moisture-loss in roots, bark &tc). Such fibres are not absorbed in the small intestine and pass straight through to the large intestine intact.

Because fibre is ‘rough’ and combines with other foodstuffs to ‘shift’ them through the digestive-tracts; it contributes to feelings of ‘fullness’/ satiety. This is a major advantage to both dieters and weight-stable people alike! The fuller you feel, the less you’ll eat!

Fibre comes in two forms:

  • Soluble fibre
  • Insoluble fibre

So what’s the difference?

Soluble fibre does as the name suggests: it attracts water and dissolves into a form of ‘gel’ in the gut. This gel helps to slow-down the digestion of other foods, including (yes!) carbohydrate and sugar. This is particularly important for diabetics. Why?  The slower the rate of carbohydrate-absorption in your system, the more stable your blood-sugars, and the lower the risk of glucose-spikes in the blood-stream.

Stable blood-sugars = better insulin management = improved health!

Examples of soluble fibres include fruits, legumes, oats (all forms of fruit & vegetables to varying extents).

Insoluble fibre is equally aptly named. It’s made of the more structural parts of plant (the lignins &tc). As a result, it also attracts water, but instead of forming a gel; it ‘puffs up’ & adds bulk/softness to other less fibrous foods. In-so-doing, it regulates the passage of foodstuffs through the intestines, thereby promoting digestive health in general.

Examples of insoluble fibres include bran, beans, green leafy vegetables, nuts & seeds.

So we know what it is and what it does. But why is fibre of special importance to a low-carb diet?

Firstly, low carb diets often consume a higher proportion of meat & dairy products than other regimes. These require good levels of fibre to secure their transit through the digestive-system

Secondly (and of supreme interest!) – because dietary-fibre is a carbohydrate which comprises the indigestible parts of edible plants; fibre should be subtracted from the total carbohydrate-content of foods, because we cannot digest it!

Yes – we minus fibre from carbohydrate whenever we calculate the carb-value of what we’re eating. This reduced figure is termed the ‘Net Carbs’ (i.e. the true nutrient-value of the carbohydrate we’re consuming; not the parts which pass straight through intact).

For many foods, this will render what seems like a high carb-value into something that’s both acceptable, and can be eaten freely on a ketogenic-diet.

Example: Carbohydrate 10g minus fibre 8g = net carbs 2g.

Sugar-alcohols should also be subtracted, but these are often hard to distinguish on UK food packaging, so are omitted from this post.

Armed with this quick and easy ‘carb-counting-tool’; shopping, cooking & ‘living’ a low-carb diet all become instantly easier and more accessible!

I hope this helps and thanks for reading,



4 thoughts on “What are Net Carbs? The role of fibre in a low-carb / ketogenic diet..

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