A runner’s guide to the glycaemic index (GI)

Here's our guide to how GI eating can improve your running and racing fitness.

So what is GI all about? And, more importantly, is it of any relevance to you as a runner? Here, we give you the facts on what GI means to you and whether it can make any difference to your running. This guide includes information and tips on:

• What GI eating is all about
• How to make a GI diet work alongside your running
• Top GI running foods

What is GI all about?
‘GI’ stands for ‘glycaemic index’, which is a ranking system for foods, based on the rate at which they release energy into the bloodstream. Foods are ranked from 1 to 100 according to how fast they are absorbed, which is extremely useful when planning your food intake for fuelling your running training.

There are two basic categories of GI foods:

High GI
These foods are rapidly absorbed by the body and provide a quick source of energy. Examples include:

• Glucose
• Sugars
• Refined products such as white bread, cakes and biscuits.

Low GI
These foods are absorbed much slower by the body and provide a more sustained source of energy. Examples include:

• Porridge
• Grains
• Unrefined products such as wholemeal bread, pulses and many vegetables.

Can GI eating help my running?
The answer to that question is yes. Practising good GI eating can genuinely mean the difference between running success and failure in both your training and racing. To understand how GI eating can support your running, think about the link between your fuel systems and running:

• During your run, you burn calories to fuel your session. The further or faster you run, the more calories you use – so by the time you finish your run, your body’s fuel tank will be partially or fully depleted. To effectively replenish your fuel stores, you need to eat carbohydrate. Carbohydrate can be either high GI (fast release simple sugars) or low GI (slow release complex type carbohydrates).

• Pre-run, eating low GI foods is ideal, as they will provide you with a sustained energy release during the run – so you won’t run out of energy mid-session.

• Post-run, eating both high and low GI foods in the correct proportions and at the correct time will maximise your recovery and enable you to load fuel at the optimum rate.

Runner’s GI protocols

Fuelling before run training
For your race or running training session, you need to take in slow release energy to provide a sustained supply of fuel for the entire duration of your run. You should therefore look to consume low GI foods such as wholemeal pasta, porridge and vegetables. If you eat high GI foods, you will get a quick energy ‘hit’ but the effects will be short-lived and will be followed by an energy low – which will significantly hamper your performance. That is why marathon runners typically enjoy a pasta party before they race; they are filling their fuel tanks with a supply of slow release energy to sustain them for over 20 miles of running.

You should also make sure you allow plenty of time for digestion before your running activity, because low GI foods take longer to leave the stomach and digest than high GI foods.

Refuelling after running training
The 15 minutes after your running session is your ‘golden window’ for optimum refuelling. During this period, your muscles are most receptive to restocking with energy, and so you should consume high GI foods because they enter the bloodstream rapidly and will quickly commence the refuelling process. Drinking a high GI drink is ideal, as it will be absorbed even faster due to it being a liquid – and will also help you to re-hydrate.

After the initial 15 minutes post-session, your absorption rate will begin to fall, so you should eat only low GI foods after the 15-minute ‘golden window’. Ideally, you should try to eat a low GI carbohydrate meal together with some protein in the period between 15 minutes and two hours after your run. The low GI food will provide you with sustained energy for your next training session and the protein content will further help the desired ‘slow release’.

GI energy tips
Apart from capitalising on the body’s ‘golden window’ after training, your diet should be completely focused on unprocessed, low GI foods so that you have enough slow release energy for sustained training. To further help the slow release process, try the following tips:

• Include fat in your running diet
  Ensure that your meals contain a small amount of fat, which will help to slow down gastric emptying (try to avoid saturated fats, however).
• Go pro!
  Including protein with each meal will further slow transit time from the stomach.
• Fruit AND fibre!
  By making your meals fibre rich – i.e. by avoiding highly refined factory-made produce, and eating wholegrain foods and plenty of fruit and vegetables – you will be getting plenty of fibre, which helps to slow down the absorption of glucose into the blood.
• Quick cook
  Reduce your cooking times – because the longer you cook carbohydrate-rich foods, the more they break down into simple sugars, and hence the faster they are absorbed.
• Unripe can be good
  The riper a piece of fruit is, the more simple sugars it contains; bananas are a good example as they become much sweeter to the taste when they are very ripe. Less ripe fruit contains more complex carbohydrates and will therefore have a lower GI.
• Timing helps
  The body’s GI response is greater at the end of the day, so for marathon runners, that evening pasta meal is timed just right for the race the following day.

GI in the long run
For the runner, there are few better nutrition plans than following the GI method. GI eating focuses on unprocessed foods, avoids simple sugars and balances meals with fibre, protein and fat – which are ideal combinations for a runner’s diet. Running primarily requires slow release energy – and because the foundation of any GI eating plan is on always eating complex carbohydrates, it will optimise your running-specific nutrition, which means that you are giving yourself the best chance of performing well.

In addition, you will find that weight management is easier, because you are saying no to high-fat and low-nutrition foods and supplying your body with a wide range of nutrients – which is essential for all-round good health.