Insoluble Fibre on Keto: Sources, Supplements and Labels
Insoluble fibre is the type of dietary fibre that doesn't dissolve in water. On UK labels, fibre is listed separately from carbohydrate, so it doesn't count towards your carbs. Low-carb vegetables, seeds, nuts and avocado all contain it, and fibre ingredients such as oat fibre and bamboo fibre are popular in keto baking.
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Keto is popular for many reasons (see can you lose weight on the keto diet?), but fibre is easy to overlook when you cut back on bread, pasta and grains. Here's what insoluble fibre is, how it fits into keto and where to find it.
What is insoluble fibre?
Dietary fibre is the part of plant foods that isn't digested like starch and sugar. It comes in two main types:
- Insoluble fibre doesn't dissolve in water. It's found in vegetable skins and stalks, seeds, nuts and the outer layers of grains, such as the oat hull used to make oat fibre.
- Soluble fibre dissolves in water to form a gel. Psyllium husk and chicory root fibre (inulin) are well-known sources.
Most plant foods contain a mix of both, in different proportions.
Fibre and the keto diet
The ketogenic diet is a low-carb, high-fat way of eating that keeps carbohydrate intake very low. Fibre is technically a carbohydrate, but on UK and EU labels it's listed separately and isn't included in the "carbohydrate" figure. That means the carbohydrate number on a UK pack is effectively already the net carbs, so you don't need to subtract fibre again.
American keto advice often tells you to subtract fibre from total carbs. That's because US labels include fibre in the carbohydrate total. UK labels don't, so take the carbohydrate figure as it is.
Keto-friendly sources of insoluble fibre
These low-carb foods all contain fibre, including insoluble fibre, and fit easily into keto meals:
- Broccoli: a versatile staple for keto meals, from stir-fries to soups.
- Brussels sprouts: lovely roasted until crisp.
- Peppers: colourful and crunchy, raw or cooked.
- Flaxseeds: add them to salads, smoothies or keto bakes.
- Chia seeds: like flaxseeds, they can be used in lots of ways, including puddings.
- Avocados: a keto favourite that contains both fat and fibre.
- Almonds: whole, flaked or as almond flour for baking.
- Spinach: easy to add to salads, smoothies and main dishes.
- Asparagus: works well in stir-fries, salads and side dishes.
- Green beans: slightly higher in carbs than some other vegetables, but they can still fit into a keto diet.
Fibre ingredients for keto baking
Fibre ingredients are also used in keto baking, where they replace some of the bulk and texture that wheat flour would normally provide:
- Oat fibre: made from the outer hulls of the oat grain and mostly insoluble fibre. Read what is oat fibre? or buy our Groovy Keto Oat Fibre.
- Bamboo fibre: made from the bamboo plant and used in a similar way to oat fibre. Read is bamboo fibre keto-friendly? or buy our Groovy Keto Bamboo Fibre.
- Psyllium husk: contains both soluble and insoluble fibre, and acts as a binder in keto bread. See our psyllium husk guide.
- Flaxseed meal: ground flaxseeds, which add fibre, binding and a nutty flavour to bakes.
- Cellulose: the main insoluble fibre in plant cell walls, found in vegetables, nuts and seeds, and sometimes added to foods as powdered cellulose.
- Hemp fibre: made from hemp seeds and mostly insoluble fibre.
- Wheat dextrin: a soluble fibre often found in fibre blends. It's made from wheat, so check the label if you avoid gluten.
- Inulin (chicory root fibre): a soluble fibre that's often included in fibre blends. Read is chicory root fibre keto?
Meal ideas
Get creative with keto recipes that include these ingredients from our keto recipes collection. Stir-fry your favourite vegetables with a protein, or sprinkle seeds over a salad for crunch. Avocado, another keto favourite, is worth adding to your keto shopping list. Here are some ideas:
Breakfast
- Chia seed pudding: soak chia seeds in almond milk overnight, add a dash of vanilla and a keto-friendly sweetener such as stevia, and top with a handful of almonds for crunch.
- Avocado and spinach smoothie: blend a ripe avocado, a handful of spinach, unsweetened almond milk and a few ice cubes.
Lunch
- Broccoli and Cheddar soup: soften broccoli and onion in butter, add chicken stock and cook until tender. Blend, then stir in Cheddar and double cream.
- Pepper and tuna salad: mix tinned tuna with mayonnaise, Dijon mustard and chopped celery, and serve in pepper halves.
Dinner
- Asparagus and almond stir-fry: toss asparagus, peppers and chicken in a pan with olive oil, garlic and soy sauce, then top with toasted almonds.
- Stuffed avocados with prawns: sauté prawns with garlic, onion and spices, then spoon into halved avocados.
Snacks and sides
- Flaxseed crackers: mix ground flaxseeds with water, leave until it forms a gel, spread thinly on a baking tray and bake until crisp. Serve with guacamole or cheese.
- Roasted Brussels sprouts: toss in olive oil, season with salt and pepper, and roast until crisp.
Tips for adding more fibre
If you're adding more fibre to your diet, do it gradually and drink plenty of water. Some people find that a sudden increase in fibre causes bloating or discomfort, and tolerance varies from person to person.
A keto diet can include plenty of fibre from vegetables, seeds, nuts and avocado, with fibre ingredients such as oat fibre and bamboo fibre for baking. Aim for a varied diet that suits you.
This article is for general information only and isn't medical advice. If you have a health condition or take medication, speak to your GP before making big changes to your diet.
Frequently asked questions
What is insoluble fibre?
Insoluble fibre is the type of dietary fibre that doesn't dissolve in water. It's found in vegetable skins and stalks, seeds, nuts and the outer layers of grains, such as the oat hull. Soluble fibre, by contrast, dissolves to form a gel. Most plant foods contain a mix of both types in different proportions.
Does fibre count towards carbs on keto?
Not on UK labels. In the UK and EU, fibre is listed separately and isn't included in the carbohydrate figure, so the carbohydrate number is effectively already the net carbs. US labels include fibre in total carbs, which is why American keto advice often tells you to subtract it. Don't subtract it again here.
Which keto foods contain insoluble fibre?
Low-carb vegetables such as broccoli, Brussels sprouts, peppers, spinach, asparagus and green beans all contain insoluble fibre, as do flaxseeds, chia seeds, almonds and avocados. For baking, oat fibre and bamboo fibre are popular because they add bulk and a flour-like texture with very little digestible carbohydrate.
Is oat fibre soluble or insoluble?
Oat fibre is mostly insoluble fibre. It's made by milling the oat hull, the tough outer layer around the grain, rather than the grain itself. That makes it different from oat bran, which contains more starch and some soluble fibre. In keto baking it adds bulk and a softer, more flour-like texture.
Are fibre supplements keto?
Many fibre supplements are psyllium husk or wheat dextrin. Fibre is listed separately from carbohydrate on UK labels, but some supplements also contain sugar, maltodextrin or flavourings that add carbs, so check the carbohydrate line and the ingredients before you buy.
