Glycaemic index (US ~ glycemic) is the measure of a food’s ability to affect the blood sugar levels. This immediate effect is usually based on the type of carbohydrates within a food. Since all foods contain a mixture of carbohydrates, protein and fat to varying degrees, the glycaemic index is relevant to all foods, not only carbohydrates. Awareness about the glycaemic index (GI) of foods is important for us all, but particularly for those suffering with diabetes and obesity.
How does GI work?
When you eat food, the carbohydrates are then broken down into simple sugars like glucose. Some foods will take longer to be processed so only a small amounts of glucose will enter into the bloodstream over a period of time. This allows your body to use this glucose for its energy needs at a reasonable rate with causing a sudden spike or dip in the blood sugar levels. These carbohydrates are known as low glycaemic index (GI) carbs. It may also be referred to as the slow-releasing carbohydrates or the ‘good carbs’.
Some carbohydrates break down quickly and flood the bloodstream with glucose. This causes an increase in the blood sugar levels. The body’s counteracts this by secreting insulin which forces cells to take in more glucose and any excess may be stored in the liver as glycogen or converted into fat. This process is flawed in diabetics and this is the reason why they may experience blood glucose spikes after certain foods. These type of carbohydrates are known as fast-releasing carbohydrates or high GI carbs. They are also commonly referred to as the ‘bad carbs’.
So the glycaemic index ranks foods according to their effect on your blood glucose levels.
Why is GI important?
If you are a diabetic or trying to lose weight then the importance is obvious. Low GI foods will not cause spikes in your blood sugar levels. This will be converted to fat or go uncontrolled as in diabetes. A diet that has more low GI foods will ensure that you have a steady flow of glucose, prevent sugar spikes and dips which may cause bursts of energy followed by tiredness and avoid the complications of diabetes or additional weight gain.
Can GI be altered?
The glycaemic index of foods can be altered to some degree. Protein and fibre are the two best nutrients to affect the the GI of foods. Ideally protein and fibre should be eaten with high GI foods to slow the release of glucose but this does not mean that you can continue on high GI foods in this manner. It only alters the GI moderately and you should still follow a low GI diet.
Is GI only important for diabetes and weight loss?
Glycaemic index is relevant to every person, whether diabetic, obese or not. By maintaining a healthy diet of low GI foods, you will feel energetic for longer, are less likely to feel the mid-morning and late afternoon lethargy and sleepiness and can maintain a healthy body weight.
What are the high and low GI foods?
A simple way of assessing glycaemic index is by understanding the processing of the raw materials that make up the food. Refined starches are usually high GI foods while foods that are less processed are usually low GI. This does not apply in every instance so you should familiarise yourself with the list of high and low GI foods. For example – white, brown and wholewheat bread are all high GI foods while low GI bread and rye bread are low GI foods. One would think that since wholewheat or brown bread is less processed then it would be a low GI food but this is not the case.
Consult with a dietitian about your individual need dietary needs especially if you are a diabetic or need to lose weight.