How to carb load for a marathon – the latest research

I know this is a bit late for most people (as I write the New York marathon is a few days away) because the long autumn marathon season has all but finished. I’ll revisit the topic next spring.

The nutitional zeitgeist at the moment seems to be directing us towards eating fewer carbs and more protein so that our carb: protein:fat ratio is 40:30:30.  The paleo diet or versions of it seem to be everywhere. Professor Tim Noakes, (world-famous and reknowned doctor, physiologist, rigorous researcher and author of The Lore of Running and Waterlogged) has settled on a regime that’s paleo-based and pretty much cuts out carbs and has improved his health in relation to his genetic predisposition to type 2 diabetes.   All these approaches are aimed at everyone, not just endurance athletes.  So if the common theme here is fewer carbs, where does that leave us on long training runs and races?

I’d urge you to listen to a discussion about the 40:30:30 approach on Talk Ultra between Talk Ultra’s Ian Corless and  Marc Laithwaiteof The Endurance Coach, a nutritionist, sports science lecturer for 10 years and member of the British Association of Sports and Exercise Scientists (BASES).  It’s not that long and very easy to listen to. The bit that struck me in relation to carb loading was Marc’s point that our muscles and liver can’t really hold that much carbohydrate – if they could, the likelihood of hitting the wall wouldn’t be so big.  So according to him, there’s not a lot of point in eating massive amounts of carbohydrate in the days leading up to a long race. Yes you don’t want to start a race depleted; it’s just that it doesn’t take a lot NOT to be depleted and if our training volume has decreased because of the taper, the carb loading is happening by default.

This is the approach I’ve taken for the last few years and I’ve not had any problems as far as I can see with running out of energy. I’ve not eaten more calories in the days before, but have tended to make more of my calories carb-based rather than from fat or protein.

However – two new studies both suggest that it’s worth upping the carbs before a marathon – but only for one day: the day before.  They’re both outlined in this New York Times article. I won’t repeat it all here but the key points are:

  • we can benefit from carb loading the day before the event
  • breakfast on the day itself seems to make no difference
  • eat about 7g of carbohydrate per kilo of your bodyweight the day before. (It’s not actually that much – for a 63kg/10 stone person needs to eat 440g of carb.)

Carb loading advice has changed over the years from fasting a few days before so that your body is ‘better’ at taking up carbs when you do start eating again, to loading up for a week beforehand, to loading up for three days beforehand.  Loading up for three or more days tends to make us feel heavy and sluggish (absorbtion of carb has water associated with it so you really might be carting round more weight than you need to) so I quite like the sound of this new info.  I’ll be trying it the day before the Brighton mara next April.  Pity it doesn’t replace training hard, too!

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