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How Important Is The GIycaemic Index And Running Performance?

The theory behind the “Glycaemic Index” was first put forward and developed by a Dr David Jenkins, in an effort to help diabetics stabilize their blood sugar levels. Not only are the principles behind the glycaemic index essential for diabetics but runners can also benefit from having a better understanding and  help them choose the correct types of carbohydrates at certain times of the day.
                                
Put simply, the glycaemic index measures the magnitude of the blood sugar response to different foods. Whenever we eat, our body has an insulin response to each type of food and in this case the varying types of carbohydrate.
For example, when we eat meat our insulin response is minimal as meat contains negligible amounts of carbohydrate. Glucose however, the simplest form of carbohydrate, produces a large insulin response. It is the body’s response to glucose to which the glycaemic index is based and all foods are compared to. On the Glycaemic index, glucose has a rating of 100 and is the food which makes the body secrete the largest amount of insulin.
 
The GI response of carbohydrate rich foods is heavily influenced by the other types of food eaten in conjunction with them. For example, if you eat a bowl of white pasta (GI of 72) with a creamy and meaty sauce, the insulin response will not be as great as it would be if you had eaten the pasta on its own as other hormones have a direct affect on the amount of insulin secreted.
 
 
 
Below are examples of common high and low glycaemic index foods:
 

HIGH GLYCAEMIC FOODS 60- 100

Bread                     Cereals                           Fruit


Dark Rye 76          Cornflakes 83                Watermelon 72
White wheat 72    Shredded Wheat 69        Pineapple 65
Whole wheat 69    Rice Crispies 82             Banana 60
Cornmeal 68         Swiss Museli 60             Raisins 60

 

Baked Goods            Grain                    Vegetables


Rice Cakes 92         White rice 92           Baked Potato 83
Doughnut 76           Cous Cous 65           Mashed Potato 75
Croissant 67           Cornmeal 68            Carrots 74

 

Sugars
Glucose 100
Honey 68

 


LOW GLYCEMIC FOOD BELOW 60%


Bread                            Cereals                    Fruits


Pitta 57                        Special K 54              Mango 55
Wholewheat Pita 55       All Bran   44              Grapes 46
Whole Rye 52                Rice bran 20             Orange 43
Pumpernickel 49           Porridge Oats 49        Apple 36
                                                                 Grapefruit 23
                                                                 Pear 36

 

Baked Goods                                Grains             

                    
Danish 59                                Brown Rice 57
Bran Muffin 59                        Whole Rye 34
Banana Cake 50                       Noodles 48

 

 

 

Vegetables                   Legumes                           Beverages


Tomato 38                Baked Beans 48                     Orange Juice 57
Cucumber 24            Green Beans 30                     Pineapple    46
Green Peas 48          Kidney Beans 27                    Milk           28
Broccoli      Low                                                 Tea             0
Cauliflower  Low                                                 Coffee          0
Cabbage    Low
Lettuce     Low
Peppers     Low
Onions      Low


Sugars


Fructose 23
Lactose 46


[source “Sports Nutrition Guide” by Michael Colgan.]

 

 

The Glycaemic Index and the Endurance runner


Applying the principles of the Glycaemic index to the runner is slightly different to that of the more sedentary person. Whereas foods high on the glycaemic index should be avoided by less active people to avoid weight gain and maintain a constant blood sugar level, for people who exercise regularly consuming high GI foods after a training run is actually beneficial to help maximise glycogen storage. This is due to the bodies demand to quickly replenish carbohydrate stores immediately after exercise. Foods high in the G.I are absorbed that much more quickly into the blood stream, helping to restock the glycogen lost during the run.
Eating a snack high in the G.I such as a banana or glucose rich energy drink immediately after a hard or long run is a fantastic way to reintroduce lost carbohydrate.

Ideal food choices immediately after a run….