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What's with all the 'carb' bashing?

Over the past few years carbohydrates have come in for a pretty rough time, with seemingly endless condemnation from fitness magazines and online ‘experts’ who have linked them to diabetes, inflammation, heart disease, obesity and almost everything else in between. This demonisation of carbs has also not been helped by the increase in popularity of diets such as paleo, ketogenic, juicing and low carb-high fat. However, such derision is unjustified.

Breaking news: carbohydrates per se don’t make you fat, over consumption however does.

Whilst the limiting of refined sugars should be encouraged, the odd beer and cake as an occasional treat within a healthy balanced diet aren’t going to do you much harm, so stop beating yourself up and treat yourself to the odd weekend treat or even a post race pie and a pint, just don't go on a two day bender. Carbohydrates are necessary in our diet, as they play a vital role in many of our biological processes. Along with being the primary energy source for moderate to high intensity exercise, they are the exclusive energy source for the nervous system, help production of melatonin and therefore sleep and are actually needed for the metabolism of fat. Whilst there has been an increase the number of athletes using low carbohydrate diets, these have primarily been used for weight reduction, not performance gains. As such, if your aim is to improve performance, then rather than dietary restriction, you should be looking to optimise your nutrition and performance through dietary periodisation.

Sport scientist and nutritionist Professor Asker Jeukendrup recently published a review titled ‘Periodized Nutrition for Athletes’ in the journal Sports Medicine. In his review he goes into detail (too much to cover here) on the various different ways we can manipulate our nutrient intake to stimulate different response. With regards to carbohydrates, we can alter the timing of our consumption to improve things such as expression of certain genes that can increase fat metabolism, stimulate a stress response, maximise recovery and train the gut to improve gastric emptying and it absorptive capacity to reduce gastrointestinal discomfort during exercise. No of which involved long-term restriction of carbohydrates.

The timing of carbohydrate intake also needs to take training intensity into account. Over recent year, there have been several studies that have looked at fasted training (just one of the many nutritional periodisation strategies outlined in Jeukendrups' paper) as a means of improving both fat and carbohydrate metabolism. A typical example of fasted training would involve performing your low intensity training sessions following an overnight fast so that liver glycogen levels are lowered and in term stimulate greater metabolism of fat. Conversely, your moderate to high intensity sessions would be performed with normal or elevated carbohydrate levels (depending upon the particular response you are trying to train). The idea being that this method will train the body to maximise fat usage at lower intensities and spare its stores of glycogen (carbs) for when it is needed more, i.e. during higher intensities and later in your race.

Below are some examples of typical carbohydrate intakes that have been suggested based on training intensity, though it is important to remember that the exact amounts will vary for each athlete:

  • light training 3-5 g/kg

  • Moderate training (<1hr)5-7 g/kg

  • Endurance athletes (1-3hrs) 7-12 g/kg

  • Extreme training>4 hrs or high intensity >10-12 g/kg

Whilst nutritional periodisation may involve the restriction of carbohydrates to some extent dependent upon your aims, the different between this and say a ketogenic diet is that this restriction is limited to relatively short periods (hours), after which normal carbohydrate fuelling will typically resume, whereas ketogenic diets generally restrict carbohydrates to less than 20-100 g per day for several weeks. Whilst there have been studies that have shown some positive benefits of ketogenic, high fat diets for performance, these improvements were not significantly greater than those participants on a carbohydrate rich diet. In addition, such studies have been limited to short period of times and have often not used trained athletes as participants. In one of the few well controlled studies on elite endurance athletes comparing ketogenic, carbohydrate and mixed diets by Burke et al. (2016), those in the ketogenic group saw a reduction in performance by 1.6% after 3 weeks, whilst those in the other groups improved by 6.6 and 5.5 % respectively. To date there is no scientifically proven evidence to support chronic carbohydrate restriction as a means of aiding athletic performance. As athletes and with that in mind, it's time to stop beating up on carbohydrates and time to start thinking about how you can embrace carbohydrates to maximise your performance.

If you’d like more information or help on optimising your nutrition, you can contact us via our website

Dr Howard Hurst.

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