Oztrack Athletics Information for Coaches

The GI factor and Sports Performance

 
  • The carbohydrate we eat is digested and absorbed too quickly because most modern starchy foods have a high G.I. Factor.
  • The G.I. Factor is a ranking of foods based on their overall effect on blood sugar levels (low G.I. means a smaller rise of blood sugar).
  • G.I represents Glycaemic Index
  • Modern diets have too many foods with a High G.I. factor.
Low G.I. Foods                                below 55
Intermediate G.I. Foods                  55 to 70
High GI Foods                                  above 70  (Glucose is the standard at 100)
 

There are times when low G.I. foods provide an advantage and times when high G.I. foods are better. For best performance a serious athlete needs to learn about which foods have high and low G.I. factors and when to eat them.

The carbohydrate we eat is stored in the body in the form of Glycogen in the muscles and in the liver.. A small amount circulates as glucose in the blood. When exercising at high intensities the main fuels are blood glucose and muscle glycogen. The body also can use fats at low intensities but loses this ability when high intensity is required. The bigger your stores of glucose and glycogen, the longer an athlete can exercise before fatigue sets in. Maintaining high glycogen stores is the key to maintaining quality training performance on a daily basis.

The beneficial effects of low G.I. foods for Athletes


Low G.I. foods are digested slowly and can remain in the small intestine for hours after consumption. The benefit of this is a slow and sustained release of glucose that occurs even during exercise.

High G.I foods release their glucose too quickly and consequently produce rapid changes in blood sugar instead of a more stable blood sugar values like Low G.I. foods.

The Pre-event meal

Low G.I. foods are best before an event and taken about 2hours before (to allow time for the food to clear the stomach). It is best to select foods that also do not cause stomach cramps and flatulence (These are usually ones with high fibre).

Consume 1g of Carbohydrate for every Kg of body weight.
1-2 hours before the start of the event.

Examples of Good Low GI foods for a 50kg athlete

Porridge                               600g  (two and a half cups)  GI=42
Sustagen                             250ml    GI about 40
Apples                                 3 small medium   GI=38
Heavy grain breads            3 slices of Burgen honey oat-bran   GI=31

During an event

Aim for 30g of Carbohydrate and 500ml of water per hour

Examples of foods that are suitable:
Sports Drinks 500-600ml per hour - Gatorade, Powerade etc.
12 jelly beans + 500ml of water per hour
Honey sandwich on high GI Bread eg wonderwhite GI=80 + 500ml water per hour

Recovery (after the event)

Muscles are more sensitive to glucose in the first hour after exercise, so a concerted effort should be made to get as many high G.I foods in as soon as possible.

Aim to consume 1 - 1.5g of Carbohydrate per Kg of body weight each 2 hours after exercise.

Examples for a  50 Kg athlete:
3 slices of a High G.I bread eg Wonderwhite        GI=80
Rice bubbles - one and a half cups + 175ml low fat milk  GI=89
Jelly Beans 25     GI=80
Sports Drinks 800ml GI=75
Lucozade 300ml original GI=95

To maximize Glycogen replenishment after competition

  • Ingest carbohydrate as soon as you can after the event and maintain a high carbohydrate intake for the next 24 hours.
  • Consume 10g of Carbohydrate per Kg of body weight over the 24 hours following prolonged exercise.
  • Choose high G.I foods in the replenishment phase
  • Alcohol delays glycogen re-synthesis so avoid it. It can also lower blood glucose levels.

  •  

    All athlete should ensure that they have a high intake of carbohydrates as it easy in hard training to become glycogen depleted which will decrease endurance and exercise performance. An athlete in heavy training should consume 500-800g of carbohydrates each day. This is much higher than the typical adult who eats only 240g a day on average.

    Athletes should aim to lower the overall G.I. of their meals by shifting their choice toward choosing to consume more low G.I. foods. There are many benefits of doing this:

  • Usually an athlete will consume less fat on a lower G.I diet as they are less hungry.
  • Eating a low GI breakfast will maintain higher blood sugar until lunchtime (many breakfast cereals are high G.I.)


Low GI Meals

Breakfast (Foods and their G.I.)
Fruit Juice and Fruits
Apple Juice 40
Grapes 46
Pears 36
Peaches 42
Oranges 44
Apples 38

Cereals (Many common ones such as Rice Bubbles are 80+)
Guardian 37
All-Bran Fruit & Oats 41
All-Bran 42
Porridge 42
Special K 54
Muesli 56

Bread (Most white bread are 70+)
Burgen Soy-Linseed 19
Burgen Oat Bran & Honey 31
Burgen Mixed Grain 34
Multi-Grain 9 Grain 43
Burgen Fruit-Loaf 44
Ploughmans Wholegrain 47
Continental Fruit loaf 47

Other meals
Lunches
Fruit salad with low fat yogurt  46
Fettucini low fat 32
Thai noodles with vegetables 36
Burgen bread sandwiches
Banana smoothie and low fat high fibre muffin

Low GI Foods
Basmati Rice 58  (Normal White Rice is 87)
Doongara 59
Sweet potato 54
Sweet corn 55
Legumes are all low
Pasta mostly 37-55
Oatmeal biscuits 55
Baked beans 48
Skim milk 32
Vitari 28
Yogurt low fat 33
Yogurt low fat (artificially sweetened) 14
Red lentils (boiled) 26
Toasted muesli 43
Tomato soup 38

Possibly surprizing higher GI Foods
Bran Flakes 74
Gluten free bread 90
Calrose white rice 87
Rice Cakes 82
Tofu Frozen dessert 115
Rye Bread 75+
Instant potato 83 (New potatoes are lower and then it depends on how they are cooked)
Baked potato 83
Steamed potato 65
Microwaved potato 83


The ideas presented are from the book:

The G.I. Factor by Professor Jennie Brand-Miller, Kay Foster-Powell, Associate Professor Stephen Colagiuri and Doctor Anthony Leeds.

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