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Tuesday, 20 February 2018

The Why, What and When of Pre Event Nutrition

There is a lot of confusing information when it comes to what and when to eat before an event. Most people are nervous and /or excited enough without having to worry about this. And the last thing you want to do is mess up all that great training by having issues during the event.

First some back ground - if you want to skip to the end for the specifics that's fine but some people like to understand the science - and it helps to validate the recommendations.

Stored Energy.
There are essentially two systems in which the body stores energy - lipid (fat) and glycolic (sugar).

For high intensity exercise like a sprint distance triathlon or a Crossfit WOD the primary fuel is glycogen (sugar). Glycogen is stored both in the liver and muscles. Logically the more muscle mass you have the greater the amount of glycogen you can store but greater muscle mass burns more glycogen in order to move so it tends to average out. The liver stores around 100g (440 calories) and muscle ranges between 320g (1400 calories) and 450g (2000 calories). As mentioned more muscle means more glycogen but also a higher burn rate so regardless of the total maximum amount stored the body stores enough glycogen for around 1 hour and 40 minutes of exercise. MORE than enough for even a long WOD like Murph.

This means that ‘carb loading’ isn’t necessary for shorter events like a WOD or 5-10km running race etc. For longer events or when doing multi events on the same day it should be noted that it takes around 24 hours to reload glycogen (1). Note that it doesn’t take any longer than that so people that carb load for 3-4 days are really just looking for an excuse to eat donuts..

Digesting Food.
Your body burns a lot of calories (energy) solely on digesting food. For a person on a 2000 calorie a day diet approximately 250 calories is burnt purely digesting this food. Interesting different macros require more/less calories to digest - Protein is the highest with about 20-30% of the calories in protein going to digesting it. Fats require the least energy with around 0-3% used. The time to digest food also varies - on average the majority of foods are digested in less than two hours (fruit and vegetables being the fastest) but high protein foods like steak, fish and eggs can take significantly longer - up to 5 hours.

Exercise and digestion.
For digestion, blood moves to the stomach to assist in this metabolic process. When we exercise blood is required in the muscles. As running away from the lion is more important than digesting it priority is given to the muscles so blood moves away from the stomach to the muscles. In hot weather blood also moves to the skin for cooling (blood/skin/sweat work like an evaporative air conditioner). So when exercising and especially in a hot environment like a gym/box, digestion slows significantly to the point where digestion stops. Undigested food rots in the stomach which does not create a pleasant experience for either yourself or the person following you into the portaloo…

Bringing this all together.

  1. Food takes around two hours to digest
  2. It’s better to do a hard workout on an empty stomach
  3. Protein is slow to digest
  4. The body doesn’t realise any energy from protein - in fact it consumes a significant amount digesting it. 
What all this means is that you should plan to have your pre event meal around 2 hours before the event. This provides enough time for the food to pass through the stomach and for blood sugar / insulin levels to normalise.

The pre event meal should be low in protein - in fact protein consumption for the 12 hours prior to the event should be low.

A typical pre-event meal would be something like a bagel with peanut butter, bircher muesli, sweet potato chips, pasta with non meat sauce, vegetarian pizza. Apologies for stating the obvious though but this isn’t the time to try a food you haven’t tried before so don’t go experimenting with something new.

A final word on hydration. The human body isn’t a camel - we can’t store water beyond what is stored within the cells. So whilst we don’t want to be dehydrated there is also no point in trying to over hydrate - in fact it can be more dangerous to over hydrate (hyponatremia) so I typically recommend drinking to thirst prior to the event (and even during)

(1) Carbohydrate loading in human muscle: an improved 1 day protocol.

Bussau VA1, Fairchild TJ, Rao A, Steele P, Fournier PA.

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