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​The endurance athlete’s guide to fibre

Posted by James Eacott on

There’s debate amongst endurance athletes around fibre. Some reference potential gastrointestinal distress but fibre is critical for overall health and even has endurance-specific benefits. Our endurance athlete’s guide to fibre explains why and how much you need as well as the best sources

33fuel endurance athlete's guide to fibre - better fuel

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What is fibre?

Often known as roughage, fibre derives exclusively from plant-based foods and is not present in meat, dairy or fish.

It’s a complex carbohydrate but unlike other carbohydrates is not digestible. Thus, it does not convert into glucose in your body and provides no energy or nutrients.

Fibre is categorised into either:

  1. Soluble fibre. It dissolves in the stomach and turns it into a mushy, glue-like substance. This ‘captures’ some compounds, slowing the absorption rate of those foods. This has positive effects we’ll discuss later
  2. Insoluble fibre. Unable to dissolve in water. Instead, it absorbs water, increases in size providing bulk to stools which aids in cleaning the lining of the intestine.

Despite providing no nutritional value, fibre plays a key role in our digestive and overall health, which of course has implications for athletic performance.

7 health benefits of fibre

For the general population, fibre has a range of benefits.

33fuel endurance athlete's guide to fibre - race longer

The benefits of fibre are varied and wide-ranging for both the general population and endurance athletes

First and foremost, fibre is really important for gut health. Carbs, fats and proteins are mostly absorbed into the bloodstream before reaching the large intestine where good bacteria resides. Fibre acts as a prebiotic, feeding the good bacteria which play a crucial role in maintaining homeostasis.

Further health benefits include:

  1. Lowers cholesterol. Soluble fibre in particular is proven to be beneficial in lowering low-density lipoprotein (LDL) or “bad” cholesterol which has the knock-on effect of lowering inflammation – a precursor to many chronic diseases
  2. Decreases likelihood of colon cancer. The third leading cause of cancer deaths, colorectal cancer incidence has been shown to decrease when fibre is present
  3. Reduce GI disorders. Insoluble fibre absorbs water and bulks stools, normalising bowel movements and reducing constipation. As this study from the University of Kentucky discovered, "Increased fibre intake benefits a number of gastrointestinal disorders including the following: gastroesophageal reflux disease, duodenal ulcer, diverticulitis, constipation, and haemorrhoids.”
  4. Reduces risk of type 2 diabetes. Fibre slows the absorption of nutrients from other foods, meaning the sugar-spike you’ll experience from some carbohydrates is stunted if fibre is also consumed. This means less insulin is triggered and therefore results in lower incidence of type 2 diabetes
  5. Lowers heart disease risk. There’s plenty of evidence showing fibre’s impact of heart health, such as this study which concluded “Consumption of dietary fibre from cereals and fruits is inversely associated with risk of coronary heart disease.” One study in the British Medical Journal went so far as to put a number of this impact and concluded that for every 7 grams of fibre consumed, your risk of heart disease drops by 9%
  6. Reduces obesity. High-fibre foods are more satiating and lead to feeling fuller for longer. This results in less calorie consumption and therefore weight loss
  7. Promotes longevity. Given the six benefits mention above, it’s clear that those with a high-fibre diet will tend to live longer.

33fuel endurance athlete's guide to fibre - lose fat

Carrying a little excess timber? Fibre could help you shift unwanted fat

Fibre for endurance athletes

All the above benefits are key for athletes too because it’s only upon the foundation of good health that athletic performance can be built. But there are some athlete-specific benefits to consuming fibre:

Athletic benefit #1: Increase lean muscle mass

Dietary fibre increases satiety and slows the absorption of nutrients from other foods, meaning you feel fuller for longer. Fibre binds with fat and sugar molecules as they travel through the digestive system, reducing the number of overall calories absorbed into your blood.

Athletes, of course, must find a balance because we still need to fuel training and racing efforts. But for those looking to shed some fat to reach race weight, fibre is certainly your friend.

Athletic benefit #2: Controls blood sugar

High fibre foods tend to sit lower on the glycaemic index. Endurance athletes in particular need to maintain stable blood sugar levels for optimal performance. The spikes and dips which result from high GI, processed and sugar-laden sports nutrition do nothing but leave us exhausted (and with a dodgy stomach).

33fuel endurance athlete's guide to fibre - stable energy levels

Fibre slows the absorption rate of nutrients – perfect for endurance athletes looking for a steady delivery of energy without peaks and troughs

Athletic benefit #3: Feeds good bacteria

As mentioned earlier, fibre feeds gut bacteria which keeps our systems firing on all cylinders and enhances immune function. A poor gut biome means less energy, poorer recovery and out-of-whack hormone production, all of which impact training performance.

Fibre and timing

Fibre slows the emptying of food from the stomach which means that consuming a lot of it close to the start of an endurance session or race can result in an upset tummy. For this reason, we recommend you refrain from fibre in the two hours before training. Some will actually lay off altogether for a day or two before a big race or competition.

Best fibre sources

If you’re looking to boost your fibre intake, it’s pretty simple - plenty of foods include a mix of both soluble and insoluble fibre.

33fuel endurance athlete's guide to fibre - brown rice

Brown rice – a fantastic source of fibre

The best sources include:

  • Oats
  • Whole grains
  • Fruits
  • Nuts and seeds
  • Brown rice
  • Vegetables
  • Beans, peas and lentils

When it comes to ‘how much?’, aim for at least 20g per day, 30g being the sweet spot.

Fibre for endurance athletes - conclusion

The health benefits of fibre are widely recognised so for this reason alone it should be a regular feature of your diet.

General health is the foundation of athletic health – how do you expect to achieve your athletic potential with an unhealthy body? – but fibre also has endurance-specific benefits such as fat loss and stabilised energy delivery.

33fuel endurance athlete's guide to fibre - premium protein

Another 33Fuel product to harness the power of plants is our Premium Protein. With 20g protein per serving from natural ingredients, this is the perfect post-training recovery fuel

More performance boosting content

From the Vlog – Be your best on race day with coach Michelle Dillon

From the Podcast – Neal Henderson – every endurance athletes’ dream coach

From the Blog

Gut health for endurance – good and bad foods

Glycaemic index and glycaemic load – what’s the difference?

Prebiotics and probiotics for health and performance

Nutrient density and sports performance

Inflammation and food


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