Glycaemic Index and how it can make you a stronger cyclist

What is Glycaemic Index?

The Glycaemic Index (GI) is a numerical indication of the effect on your blood glucose levels of 50g of Carbohydrate (CHO) from a particular food.  Carbohydrate in the form of glucose is used as a reference point and scores 100 on the GI scale.  A score of less than 55 is considered low GI and greater than 70 is considered high GI (Hang with me on this....)

 So how does that help me? 

Knowing that alone doesn’t but, if you know also that high GI foods are rapidly digested and cause a large rush in blood glucose levels, followed by an equally rapid fall.  Whereas low GI foods are more slowly absorbed, don’t produce a spike in blood glucose and provide a steadier energy release over a greater time (remember both are still delivering the same amount of energy) you begin to see that you can choose foods to best fuel your body in any given situation. 

Like What? 

Well, for example.  Before heading out for the Sunday run eating a high CHO, low GI breakfast (eg. Porridge or beans on toast) will mean that you last much longer into the ride before you begin to fatigue. This is because your muscles are constantly being provided with glucose from the blood thus sparing the reserves kept in the muscles.  This is a very real advantage as when these muscular stores of glycogen are used up, a condition known as Glycogen Depletion, you have “hit the wall”, “bonked” etc.  Put like that the advantages that this knowledge allows you become clearer.  Add in a bidon of sports drink* (moderate GI) instead of water and some high GI snacks (eg. Banana, honey sandwich etc) to keep your blood glucose topped-up and you have a winning formula to keep you riding stronger for longer. 

Okay so low GI good high GI bad right? 

There is a time and a place for everything, horses for courses and all that.  Applying the knowledge we now know we can see that eating high GI foods will produce a surge in blood glucose and there is a time when this is very desirable indeed.  Following exercise your body is crying out for glucose to replenish those muscle glycogen stores.  You have about a 2-hour window in which time the enzymes responsible for replenishing glycogen stores are at their most active, your body will greedily stash away as much glucose as it can cram into your muscles (up to 60g/hr).  At this time high GI foods are exactly what will serve your needs best so break out the honey sandwiches and Mars bars at the coffee shop, your legs will thank you for it! 

* If you want to sample the benefits of a sports drink then you’ll be glad to know that you can make your own with the same energy, osmolality and electrolyte content as commercially available versions.  Mix your choice of fruit juice with an equal amount of water and add a flat teaspoon of salt for every litre of mixture.  Bingo instant rocket fuel!