The Glycemic Index and Maximising Sports Performance

sports performance

The Glycemic Index can be a helpful tool to maximise the availability of energy for both athletes and people who are seeking a healthy diet.

What is the Glycemic Index (GI)?

The glycemic index is a scale used to classify foods containing carbohydrate including breads, pasta, rice, cereals, dairy products and drinks. Each food or drink is given a score from 1-100 depending on the rate at which the food is broken down by the body, and the resulting impact it has on blood glucose levels.

The ranking of GI foods is as follows:

  • Low GI foods – 55 and under
  • Medium GI foods – 56-69
  • High GI foods – 70 and above

Carbohydrate-containing foods that break down slowly and supply glucose to the body steadily are known to have a low GI. For many people foods with a low GI are great s the basis for meals and most snacks.

Carbohydrate-containing foods that break down quickly and release a rapid supply of glucose are known to have a high GI. Pure glucose is the most rapidly absorbed form of carbohydrate and has a score of 100. In sports nutrition, high GI carbohydrates are often helpful to supply additional fuel during exercise.

Note: Some foods do not have a GI value as they don’t contain any carbohydrate, e.g. Meat, fish, eggs, oil, margarine and cheese.

What can affect the GI value?

There are many factors that can affect the glycemic index including how the food is processed, prepared and cooked. For example, potatoes will vary in GI value depending on how old they are.

Other things that affect GI include:

  • The type of starch in the food – Different types of rice have different GI values as they contain different types of starch.
  • Fat and protein eaten at the same time as carbohydrate can delay emptying of the stomach and in turn, will often slow the absorption of carbohydrate
  • The amount of fibre in a food can affect the glycaemic index, often with fibre making a food lower GI.

It is therefore important to use GI as a tool within the realm of what you already know about healthy eating. There are some peculiar cases with GI, such as low fat ice-cream having a low GI. This is because of its protein and fat content, so it doesn’t necessarily translate that food with a low GI will always make for a snack you will choose every day. To make healthy food and drink choices, it’s important to use GI alongside the nutrition guidelines.

Putting GI into practise

Use a low GI bread and a low GI cereal. Eg Rolled Oats, Whole-grain bread.

Include at least one low GI good at each meal.E.g. Combine fettuccine pasta with grilled chicken.

Keep foods ‘whole’. E.g. Intact wholegrain rather than wholemeal or white bread: whole fruit rather than fruit juice; raw and unpeeled fruit and vegetables or just lightly cooked.

A low GI food combined with a high GI food within a meal can give a moderate GI for that meal. E.g. natural yoghurt dressing with potato salad.

How can you use the glycemic index in sport?

Carbohydrate rich foods are an essential part of the diet. They are the preferred source of fuel for exercise and the only type of fuel that the brain can use.

The glycaemic index can be a useful tool in sports nutrition to maximise the availability of energy at any given time. Foods with a low GI can be helpful to supply a slow release of energy during exercise. High GI food or drink can also be helpful to provide instant fuel during exercise.

The pre-exercise meal

A carbohydrate rich meal within the 4 hour period before exercise has been show to improve endurance and performance for prolonged, moderate intensity exercise. More research needs to be done before specific guidance can be given about the exact type and timing of carbohydrate intake before exercise. This is because it depends very much on the individual and the type of exercise they are performing. However, for most people it is helpful to have a meal or snack with a moderate to low GI a few hours before exercise to supply a steady release of fuel before and during exercise. If you exercise after work or school, it will be important to include a meal or snack sometime during the afternoon.

Some ideas include:

  • A grainy bread sandwich with tuna and salad.
  • Smoothie with low fat milk, yoghurt, small banana and oats
  • Hot oats with berries and low fat milk
  • Chicken pasta salad
  • Bran and berry muffin with low fat yoghurt

For those who train very early in the morning, or find lighter snacks work better for them before training, cereal bar, fruit and yoghurt, creamed rice or smoothies are suitable.

During Exercise

For prolonged exercise your body is likely to need additional carbohydrate to fuel the workout and improve exercise capacity and performance. You should ideally consume food and/or drink which is easy to digest and will be rapidly absorbed by the body, providing an instant supply of energy. To achieve this, high GI options are likely to be helpful, with the aim of including 30-60g of carbohydrate per hour of intense, prolonged exercise.

High GI ideas include:

  • White bread with jam or honey
  • Jelly beans
  • Pikelets or crumpets
  • Sports drinks and bars
  • Sports gels taken with water

After exercise

The goal after exercise is to replenish muscle glycogen (carbohydrate stores) and allow muscles to recover and repair. If you are exercising a couple of times a week, a carbohydrate rich snack like a baked fruit bar, fruit and yoghurt, sandwich, creamed rice or your planned next meal is likely to be adequate for recovery. If training sessions are every day and/or twice a day, a more rapid approach to recovery drinks and snacks might include sports drinks, ripe bananas, honey or jam on white bread, pikelets or crumpets.

For more information seek individual advice from a Dietician or Sport Nutritionist or qualified personal trainer.

GI Value of Common Food / Drink

Low GI = 55 and Under

  • Heavy, dense grainy breads e.g. Burgen, Vogel’s, pumpernickel
  •  Rolled Oats, All-bran muesli
  • Pulses e.g. lentils, chickpeas, kidney beans
  • Grainy cracker
  • Paster, instant noodles, egg noodles
  • Milk, yoghurt, low fat icecream
  • Fresh: apples, bananas, kiwifruit, strawberries, oranges, peaches.

Medium GI = 56-69

  • Wholemeal bread, pita bread, crumpets, fruit bread
  • Weet-Bix, Mini Wheats
  • Basmati rice, brown rice, couscous
  • New potatoes
  • Fresh: apricots, mango, pawpaw, pineapple, ripe bananas
  • Raisins, sultanas

High GI = 70 and above

  • French bread, English muffins, bagels, scones
  • White rice, jasmine rice
  • Bakes, mashed potato
  • Pumpkin, swede, broad beans
  • Sports drinks, jelly sweets, honey, glucose
  • White crackers, rice crackers

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Not all GI is equal

Not all foods with a low GI are ideal food choices e.g. chocolate, potato chips!

Select foods that are low in fat and sugar, high in fibre and less processed. If your present eating patterns include very few low GI foods, try to introduce these slowly and monitor the effects on your blood glucose levels.

Before a competition/ race you may find that some low GI foods are too high in fibre, so you may need to choose other carbohydrate rich foods that you tolerate well.

By Ian Duncan

PT Courses