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Guide to Diabetes

The Glycaemic Index (G.I)



The Glycaemic Index or G.I. diet has been in the news recently but what does GI mean and how is it helpful for weight management and blood glucose control?  The glycaemic index is a way of measuring how quickly a food causes the blood glucose level to rise after we have eaten it. All foods that contain sugar or starch (carbohydrate) are broken down in the gut into glucose. The glucose is then absorbed into the blood stream causing the blood glucose level to rise.


What does it Measure?

The glycaemic index measures how quickly the glucose level in the blood starts to rise. If a food has a high GI then glucose from that food will be absorbed quickly and blood glucose level will start to rise quickly.

Foods that have a low GI are slowly absorbed and the blood glucose level rises more slowly and gradually.


Complex Carbohydrates And Refined Carbohydrates


Complex Carbohydrates.
The concept of GI was first discovered in the 1980’s. Prior to this it was thought that foods such as brown bread, brown rice and whole grains were absorbed slowly and therefore led to a gradual increase in blood glucose. Thus often called complex carbohydrates

Refined carbohydrates.
Foods that had been through more processing such as white bread, sugar and flour were thought to be absorbed more quickly and cause the blood glucose level to rise more quickly.

More recent research has shown that things aren’t quite so straightforward!
The GI has shown that some sugary foods like chocolate are quite slowly absorbed (GI 44) and some foods that you might expect to be slowly absorbed like wholemeal bread have a high GI (GI 77) And are absorbed quickly.

Other things that affect how quickly foods are absorbed include;

  • The amount of fat and protein in the food
  • The difference between our individual bodies and digestive systems
  • How well we chew our food
  • How the food is cooked
  • How ripe foods are
  • The other foods that are being eaten at that meal


How Can GI Help With Blood Glucose Control?


Choosing foods that have a low GI can help to slow down and reduce the rise in blood gluose levels after eating.

If you are controlling your diabetes with lifestyle changes (with or without tablets) choosing more low GI foods as part of your healthy lifestyle can help you to get your blood glucose level into the target range.

Foods with the highest GI are sugary drinks such as cola, lemonade and fruit juice, these drinks cause the blood glucose to rise very quickly.Drinks with a very high GI are therefore the best treatment for a 'hypo'! ie If your blood glucose level goes below 4mmol/l this is called a hypo. If this happens you should treat it immediately with something that increases blood glucose levels very quickly such as Lucozade, cola, pure orange juice or dextrose tablets.

How Can GI Help With Weight Management?


Foods and meals with low GI release sugar more slowly into the blood. For some people this helps you to feel satisfied for longer after the meal. This can mean that you feel less hungry between meals and are able to have fewer snacks and eat less. 

Here are some basic guidelines;

  • Whole grain and wholemeal products like brown pasta and rice, wholemeal and wholegrain bread and cereals are still healthy choices as they provide fibre in our diet which helps with bowel motions and vitamins and minerals for a healthy body regardless of their GI.
  • Foods that contain whole grains such as grainy/granary bread and whole grain cereal have a low GI.
  • Eating lots of salad or vegetables with a meal helps to slow down how quickly glucose appears in the blood.
  • Including pulses-like lentils, chick peas, garden peas, beans and sweetcorn in a meal helps to slow down how quickly glucose appears in the blood.
  • Sugary drinks have the very highest GI. If you avoid these when your blood glucose level is within the target range you can help to reduce the number of high blood glucose (hyperglycaemia) levels you get.
  • Use drinks and foods with the highest GI to treat hypos.


Blood Glucose Control And Glycaemic Index


Imagine that the model is your plate. An easy way to think about your portions is to aim for

  • half (½ ) your plate to be filled with vegetables or salad.
  • A quarter (¼) for meat, fish or vegetarian alternatives
  • A quarter(¼) for starchy foods like cereals, bread, potatoes and rice


How it works


  • Glucose is released into the bloodstream when we eat and digest foods that contain starch or sugar (carbohydrate foods).
  • Allowing 1 quarter (1/4) of your plate for starchy foods helps to control the portion of these foods that you eat at meals. If you have similar portions of starchy foods at mealtimes it helps to control blood glucose levels from one day to the next. This may also help you to control your weight.
  • Some carbohydrate foods release glucose into the blood more quickly than others.
  • Having lots of vegetables or salad and a portion of meat, fish or a vegetarian choice (such as beans or lentils) helps to slow down the glucose that is released from the starchy foods. It may also help you to feel less hungry between meals.
  • If you are trying to lose weight you should try to choose low fat dressings and sauces, remove the visible fat from meat and avoid frying meat and fish as much as possible.
  • By choosing foods that have a lower GI, as well as using the plate model above, you can help to control the level of glucose in your blood after meals and this may also help to control your appetite.
  • Below is a list of Food with their glycaemic index

Download the table below which  shows the GI of some common foods, choosing foods from the “low GI” column more often may help to control your blood glucose levels and appetite.


Glycaemic Index

Information about the Glycaemic Index (GI). Download Document