Carbohydrates in Performance and Recovery Nutrition.

By Michael Naylor MSc SENR & DuelFuel’s Nutrition Team


 “The lack of carbohydrates can make you a little crazy”

– Tom Hardy

“I keep my diet high in protein and low in carbohydrate”

– Sullivan Stapleton

Two actors with two completely different perspectives on carbohydrates, albeit one actor slightly better known than the other!

There’s no doubt about it, carbohydrates are controversial. Mention the word “carbs” in a gym and you’ll split the room; some will swear by them and others will swear at them.

Even defining or naming a type of carbohydrate can be controversial, so we thought we’d lift the lid on “carbs”.

The British Dietetic Association, the UK’s professional association for dietitians, classifies carbohydrates in three types; sugars, starches and dietary fibre.





A simple sugar or “monosaccharide” is a carbohydrate with one unit of sugar

Fructose, e.g. fruit juice

Glucose, e.g. honey, soft drinks

Glucose is also the main form in which carbohydrate circulates in our body

A disaccharide is a carbohydrate with two units of sugar

Sucrose, e.g., table sugar

Lactose, e.g. milk sugar


Complex carbohydrates or “polysaccharides”, with more than two units of sugar linked together

Starch in cereal grains, including wheat, bread, flour, rice, pasta.

Potatoes, root vegetables and pulses.

Dietary Fibre

Carbohydrates in plants. These are known as “non-starch- saccharides. We cannot digest them, but they are a major part of dietary fibre

Root vegetables, nuts, seeds, oats, fruit, cereals, wholemeal bread

Table1: adapted from the BDA (2016)

Y’might be thinking “jeez, Mike….why so early with the geeky ‘saccharide terminology?”. Fear not. As we’ll see, the important thing to remember here is monosaccharides and disaccharides are “simple” and “polysaccharides” are complex.

How The Body Absorbs Carbohydrates

So, now we know carbohydrates are often classified “simple” and “complex”, how do we use them?

We break down most carbohydrates in the gut, where they are absorbed into the blood stream in their individual sugar units.

Simple carbohydrates usually digest faster than the complex ones, purely because they take less time to break down. The term “simple” gives that away, right? The ease at which these simple sugars break down results in a rapid rise in blood sugar. Hint – if you exercise, you might want to remember this point.

Our complex carbohydrate friends take longer to break down into their individual sugar units before they can be absorbed, resulting in a slower rise in our blood sugar levels.

What Happens After Carbohydrates are Digested?

Once carbohydrates have been absorbed into the blood stream they are now in the form of glucose, where it is either carried into cells such as the muscles and brain with the help of the hormone insulin or converted from glucose to glycogen and stored in the liver and muscles for later use.

So What’s the Glycaemic Index?

As with many things related to nutrition, we are continually learning and there is an ongoing discussion over the most helpful way to classify and measure carbohydrates. Current thinking is that classifying carbohydrates as “simple” and “complex” does not give the full picture, whereas using the glycaemic index (GI) may do.

The GI measures how quickly and how much a carbohydrate raises blood sugar.

High-glycaemic foods like white bread raise blood sugar high and at speed, whereas low-glycaemic foods raise it gently and to a lesser degree. Some research has linked high consumption of high-glycaemic foods with a range of health-related issues, however high-glycaemic foods can provide energy during high intensity and/or prolonged activity. They can also be used to restore muscle glycogen stores after exercise.

GI is a well-known dieting tool, but it does have its restrictions, as it measures foods per 50g of carbohydrate provided and not by portion size, and so foods like carrots are included in the high GI list along with other important fruits and vegetables. 

This is where Glycaemic Load comes in!

Glycaemic Load (GL) is a calculation that takes into account the GI of a food and the available carbohydrate content in a serving of that food. Like Gl, the higher the GL, the faster the expected rise in blood sugar.

To explain, let’s look at an example from the British dietetic association (2016) which shows carrots have a high GI but a low GL.

This is because GI is based on the rise caused by consuming 50g of carbohydrate from any food. So to get 50g of carbohydrate from carrots you would need to eat around 700g of carrots– about five whole carrots to cause this blood sugar rise. As a portion of carrots eaten is much closer to 60g than 700g, carrots can be considered as having a low GL and therefore can be included in your diet.

So What’s Going On in The Elite Performance World?

In recent years the press has been full of different views on high and low carbohydrate diets.

From an elite sports performance standpoint, a common approach in the athletic world at present is carbohydrate periodisation or ‘fuel for the work required’.

During both intense, intermittent exercise and prolonged steady-state physical activity, the sugars stored as glycogen in muscles are converted back to glucose, which the body then uses for fuel.

The speed at which this glycogen is converted back to glucose depends upon the type and duration of exercise being undertaken; the greater the exercise intensity, the greater the rate at which glycogen is used up. As a result, high-intensity activity, such as repeated sprinting, can quickly use up our glycogen stores, even though the total time of activity might be relatively brief. In comparison, an endurance athlete who trains for hours at a time will also use up their glycogen stores, but at a slower rate.

The key point here is to align carbohydrate intake with planned duration and intensity of exercise. For instance, on days that involve only light physical activity of relatively short duration, considerably less carbohydrate is required to restore muscle and liver glycogen stores than on heavier training days. For that reason, current recommendations for carbohydrate intake in athletes vary to reflect the daily training load.

What Does That Mean For Me?

Current recommendations can be as much as 8–12 g carbohydrate per kilo of body weight to fully replenish muscle glycogen stores for people undertaking prolonged and/or intense activity1 2. However, many athletes, both professional and enthusiast, do not consume enough carbohydrates to meet recommended intakes. See table 2 for further recommendations for various training programs 

Type of Activity

Minutes of Activity

per Day

Recommended Carbohydrate Intake (grams/kg body weight)

Very light intensity training programme

Less than 60


Moderate intensity training programme



Moderate to high intensity endurance exercise training programme



Moderate to high intensity exercise training programme

Longer than 180


Table 2 – carbohydrate requirements for various exercise intensities

The consequences for an active person of not consuming enough carbohydrate are….

  • Limited glycogen stores which can reduce performance in high intensity and prolonged exercise
  • Potential to reduce cognitive function during prolonged exercise
  • Limit energy levels

On rest or lighter exercise days you may not require as much energy and carbohydrates so you adapt your carbohydrate intake as necessary.

Five Common Myths Around Carbohydrates

Carbohydrates are Unhealthy

Carbohydrates can play a pivotal role in supporting energy levels and many foods that contain carbohydrates are a great source fibre and can provide an array vitamins and minerals to support health too.

Eating Carbohydrate Causes Increases in Fat Mass

Every gram of carbohydrate can be stored with upwards of 3g of water, which can sometimes increase short term body mass. However, carbohydrates do not increase fat mass unless over consumed.

Low-Carbohydrate Diets are the Best Way to Lose Body Fat

Sometimes low carbohydrate meals or low carbohydrate days may be beneficial to support body composition. The key to fat loss is a healthy calorie deficit.

Don’t Eat Carbohydrate Before Exercise

Sometimes training in a low carbohydrate state can have some physiological effects to increase mitochondria; the engine component of the cell. However, this should be done in a controlled manner with support from a registered nutritionist or dietitian as it could have adverse effects.

Carbohydrates Consumed After 6pm Will Increase Fat Mass

The majority of research suggests the timing of calorie intake has less influence on increasing fat mass than a consistent calorie surplus.

Key Take Aways

  • Carbohydrates are often classified simple and complex
  • Carbohydrates are absorbed into the blood stream as glucose, or blood sugar
  • Simple carbohydrates may often raise blood sugar levels at a faster rate than complex carbohydrates; this speed is measured on the glycaemic index
  • Aligning carbohydrate intake to the type, intensity and duration of exercise can support performance and recovery during the activity
  • Not consuming sufficient carbohydrates can lead to impaired energy for intense and/or prolonged exercise

There you have it…carbohydrates, debunked.


[1] Thomas TD, Erdman KA, Burke LM.. Nutrition and athletic performance. Med Sci Sports Exerc. 2016;48:543–568. [PubMed] [Google Scholar]

[2] 4. Burke LM, van Loon LJ, Hawley JA.. Post-exercise muscle glycogen resynthesis in humans. J Appl Physiol. 2017;122:1055–1067. [PubMed] [Google Scholar]


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