Low-Carb Rhubarb Crumble – a quintessentially British dessert, but ketofied!


Lovely, ultra-low-carb, rhubarb has been back in season recently here in the UK, so it inspired me to make a Low-Carb Rhubarb Crumble!

Here’s the recipe, plus a link to one for a low-carb crème anglaise/English custard to serve with it.

Jump to:

– Recipe for Low-Carb Rhubarb Crumble
– Nutritional Info
– Some Health Impacts of the Main Ingredients


Whatever the weather, rhubarb crumble is a delicious, mega-traditional British pudding. In the winter months, it’s fab and comforting served warm with thick hot crème anglaise/English custard. Or in the summer months, you might serve it at room temperature with the same custard chilled and thickened. Or try it with fresh double/heavy whipping cream poured over it – or with whipped cream or ice cream on the side.

My own recipe for crème anglaise/English custard, which I like to use to accompany Low-Carb Rhubarb Crumble, is here. You can either use it as a hot pouring sauce as soon as it is made. Or you can let it go cold and set as a thick cream before serving.

I like to buy rhubarb in bulk when it’s in season and cheap. Then I chop and freeze a good quantity so I’ve got some to see me through the winter. But outside the fresh rhubarb season, you can also look in your local stores for chopped fresh rhubarb which has been frozen without added sugar. In the UK, you can currently buy that online from Ocado, and you can sometimes find it in Asda.

If you’re not low-carbing, or otherwise managing your sugar consumption, then you can also buy rhubarb tinned in sugar syrup in most supermarkets.

The humble crumble

The crumble is a traditional, quintessentially British dish –  a national institution really, but one that’s been exported around the world. Crumbles are most commonly sweet, but can also be savoury. It was during World War II, when pastry ingredients were rationed in Britain, that crumbles grew significantly in popularity, as a practical alternative to pies.

Sweet crumbles involve a crumbly topping baked until crisp over fruit – such as rhubarb, apple, plums, or a combination. The sweet crumble topping is traditionally made of brown sugar and butter, plus some combination of flour, rolled oats or nuts.

Converting a crumble to low-carb

So whereas rhubarb is naturally low-carb, crumble most definitely isn’t! So I needed to make some adaptations to make Low-Carb Rhubarb Crumble.

In place of brown sugar, I’ve using my old favourite low-carb sugar substitute erythritol. You can read here about what it is and its nutrition and health profile. I’m using the brown version from the Sukrin brand for this recipe. But you can use any other brown or white granulated sugar substitute. Or you can use sugar itself, of course, if you’re not low-carbing.

In place of flour/oats, I’m simply using ground almonds, with a little ground flaxseed.

I’ve also added a little xanthan gum to the rhubarb. It’s a common low-carb thickener readily available in supermarkets. It’s optional in this recipe. But if you add it to the rhubarb, then as it cooks and releases its juices, they will mix with the xanthan gum and make the fruit a little thicker for supporting the crumble topping.


Nutrition Info

I’ve chosen to use rhubarb for my crumble – as opposed to any other fruit – not only because that’s very traditional, but because it’s one of the lowest carb fruits on the planet.

Rhubarb has only 0.8g of total sugars, and 7 calories, per 100g. To see how ultra-low those numbers are, let’s compare them to blackberries, also traditionally used in crumble. Blackberries are also hailed as very low-carb, and they are. But having 5.1g total sugars, and 25 calories per 100g, they still weight in heavier than rhubarb.

Low-Carb Rhubarb Crumble contains around 3g net carbs per serving, so you’re saving around 30g over a similar size portion of a regular supermarket crumble. You’re trading that for a greater quantity of healthy fats from the almonds and flaxseed, and a little more protein and fibre.

Approx. Per portion (1/6 of the crumble) Low-Carb Rhubarb Crumble Regular UK supermarket (Tesco) Rhubarb Crumble
Net Carbs (i.e. minus: polyols in erythritol; & fibre, which is counted separately) 3g 32.6g
Kcal 224 212
Protein 6g 3.7g
Fat 20g 7g
Fibre 4g 2.3g

Figures calculated using verified nutritional info on MyFitnessPal. 


Some Health Impacts of the Ingredients

Let’s have a quick look at the health profile of Low-Carb Rhubarb Crumble’s main ingredients. I’ve written previously about almonds, full fat dairy (butter), and erythritol sweetener.  And save to say that it’s a significant source of omega 3 fatty acids – in which many of us are deficient – I want to leave flaxseed for a more in-depth look another day.

So that leaves us with rhubarb.


Rhubarb has rich amounts of Vitamin K. That helps wound-healing, as it’s needed for blood clotting. And it may also play a role in bone health.

It’s also high in beta-carotene, an antioxidant which the body can convert to vitamin A. Vitamin A is essential for supporting your immune system, and for healthy vision, skin and membranes. The carotenoids lutein and zeaxanthin, also strongly present in rhubarb, may also help to protect the retina in the eye and guard against macular degeneration, although more research is needed on this.

To maximise absorption of fat-soluble carotenoids and vitamin K, rhubarb is best eaten alongside fat. That’s good news for eating this Low-Carb Rhubarb Crumble, which contains a good portion of healthy fats.

Minerals-wise, rhubarb is a significant source of potassium and chloride – which are both particularly important if you’re a keto dieter. That’s because they’re electrolytes which contribute to keeping your fluid balance and blood pressure in check. Well-balanced electrolytes may well help guard against the ‘keto flu’, which you may experience for some days when first starting a low-carb diet.

Rhubarb also contains significant amounts of calcium. That’s necessary for assisting strong teeth and bones, regulating the heartbeat and other muscle contractions, and maintaining normal blood clotting. Calcium deficiency may lead to rickets in children, and osteoporosis or osteomalacia for older adults.

Rhubarb is also reported to be a good source of antioxidants. But there’s some debate, and further research needed, about whether antioxidant levels are decreased or increased by cooking, and about their conjectured therapeutic properties e.g. against cancer.


Recipe for Low-Carb Rhubarb Crumble & Custard


Recipe for Low-Carb Rhubarb Crumble & Custard

  • Servings: 6
  • Difficulty: Moderate
  • Print

Low-Carb. Keto. Vegetarian. Free from gluten, added sugar & artificial sweeteners.


  • 350g/around 4 stalks fresh rhubarb stems (weighed after leaves have been removed)
  • 28g/1oz ground/milled flaxseed
  • 112g/1 cup ground almonds/almond flour
  • 56g/¼ cup cold, unsalted butter, chopped into small cubes
  • 5g/1 tsp xanthan gum
  • 60g/4 tbsps low-carb brown granulated sugar substitute (I use Sukrin. Use white granulated sweetener if you can’t get brown, but brown gives a slightly better flavour.)


  1. Preheat your oven to 180°C/160°fan/350°F/Gas 4.
  2. Chop the rhubarb into 1 inch slices. Put them into a ovenproof casserole dish which is shallow, but big enough to leave at least an inch gap above the rhubarb for the crumble topping.
  3. Sprinkle half (30g/2 tbsps) of the granulated sweetener over the rhubarb, add the xanthan gum – if using, and mix all together.
  4. In a separate medium bowl, mix ground flaxseed with the ground almonds and the other half of the sweetener. Put the cold butter cubes into this mixture. Rub the butter cubes into the dry ingredients with your finger tips until the mixture resembles fat crumbs.
  5. Sprinkle this crumble mixture on top of the rhubarb so it is evenly covered.
  6. Bake the Low-Carb Rhubarb Crumble in the oven for 35-40 minutes until golden brown on top, and the fruit is soft underneath.
  7. If you’re going to serve your rhubarb crumble straight away with custard, then you can be making that while the crumble is cooking (custard recipe here). Alternatively, serve Low-Carb Rhubarb Crumble with double/heavy whipping cream poured over it, or with ice cream or whipped cream on the side. the crumble is also lovely served cold, and reheats well in a microwave, or covered in the oven.


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