The Glycemic Index


Ever wondered the best way to fuel your body before an intense workout at the gym? Or perhaps you struggle to make it through a busy day at work without feeling tired or lethargic. Well, the Glycemic Index could just be the answer to your problems when you feel yourself running out of steam.

The Glycemic Index
The Glycemic Index (GI) is a nutritional tool designed to measure how rapidly a carbohydrate is absorbed from the small intestine into your bloodstream. Generally speaking, the faster a carbohydrate can enter the muscle cells the more rapidly energy will be available to the body.

Scientists developed the GI to give a more accurate description of how different foods will affect blood sugar levels. When a carbohydrate has passed through the small intestine and has entered the blood stream it is ultimately available as a source of energy. Foods are ranked on a scale of 0 to 100 based on their immediate effect on blood sugar where they are compared to a reference food such as Glucose. The resulting reference number ultimately represents the speed of which the carbohydrate can be presented to the muscle to be used as energy; a high GI carbohydrate will enter the blood stream rapidly whilst a low GI carbohydrate will create a slower and more sustained response. As an example, mashed potato has a GI of 70 which means it produces a rise in blood sugar which is 70% as great as that produced after eating the equivalent amount of Glucose.

To date, scientists have calculated the GI of around 700 foods which will fall in to 1 of 3 categories:
Low GI (less than 55): Ultra Fine Scottish Oats, Palatinose, Brown Pasta, Lentils, Pulses.
Medium GI (56-69): Potatoes, Chocolate, Noodles
High GI (70 or more): Dextrose, Maltodextrin, White Rice, White Bread.
These categories make it easier for you to choose which carbohydrate will suit your time of consumption, especially in and around exercise.

Consuming the correct food at the correct time can boost fuel availability and enhance physical performance. It is, therefore, crucial that you carefully consider exactly what you eat before during and after exercise to get the most out of your physical capabilities.

Consuming a High GI carbohydrate or a Low GI carbohydrate before exercise is a hotly debated subject. A vast amount of research has been performed at the University of Sydney to support the use of Low GI foods before exercise as they believe this provides a sustained supply of energy during exercise. Research found that when a Low GI food, such as Ultra Fine Oats, was consumed 1 hour before exercise a group of trained athletes were able to exercise considerably longer than when they consumed a High GI meal. Other studies have also shown that a Low GI meal before exercise produces greater blood sugar and fatty acid levels during the latter stages of exercise. This clearly shows that Low GI foods are extremely advantageous to anyone taking part in endurance sports.

During and immediately after exercise, it has been suggested that the consumption of High GI carbohydrates, such as Dextrose, is much more preferable. As High GI foods have a much more marked and immediate influence on blood sugar levels, this provides the body with an immediate supply of energy. The eating of high GI carbohydrates after exercise increases plasma glucose and insulin concentrations and this facilitates muscle glycogen resynthesis, thus preventing the breakdown of actual muscle tissue for energy.

Away from exercise Low GI foods have been shown to support a number of health benefits over High GI foods, including:

Reduced risk of Type 2 Diabetes
Reduced risk of heart disease
Greater control over body weight
Reduced cholesterol levels

It is also suggested that consuming High GI foods generally make blood glucose levels higher which can lead to a number of health issues. Glucose spikes stimulate hunger because you are getting that dramatic drop in glucose, 90 minutes to two hours after eating. By eating Low GI foods you feel fuller for longer and are, therefore, not as likely to go searching for snacks every two hours. Insulin is a storage hormone that stockpiles nutrients for later use by the body. Therefore, High GI foods can cause a lot of insulin to be produced and when you have too much insulin in your body too much of the time, it makes it easier to store fat and harder to burn it.

A diet combining High and Low GI foods is vital for a varied diet and also for energy production. There are obvious times that certain level GI foods are more appropriate than others, but it should be recognised that the Glycemic Index is a great tool for a healthy diet.

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