Glycaemic Index Diet

This again recommends a high carbohydrate, high fibre, low fat diet – around 45-65% carbs, 15-35% protein and 25-35% fats. How it differs from other such diets is by the use of a scale that ranks carbohydrate foods according to their Glycaemic Index (GI).

So, what do I mean by GI? As we already know certain foods affect our blood sugars more, or less, than other foods and convention favoured complex carbohydrates over sugars because they felt that the process of breaking them down into sugars would take longer and thus give us lower BG levels.

A change in this thinking came about in 1981 when a Professor of Nutrition at the University of Toronto, Dr David Jenkins and his team, discovered, to their surprise, that what we had come to accept as bad carbs raised our blood glucose levels faster than good carbs!

So he developed what he termed the ‘Glycaemic Index’, a way of ranking individual carbohydrate containing foods, gram for gram, according to the effect they have on blood sugar levels. Only carbohydrate containing foods appear on the GI index.

You won’t find high fat or high protein foods such as fresh meat, chicken, fish, eggs, nuts and cheese in GI lists. Also many fruits and vegetables contain very little carbohydrate per serve, so have such low GI values they are regarded as “free” foods. Processed foods, like sausages or chicken nuggets, contain some flour so they do appear on GI lists.

How it works.

A reference point was needed from which to compare all other foods. Pure glucose was chosen as this point and given a GI of 100. All other foods are ranked from 0 to 100 according to their effect on blood sugar levels.


  • 70 or over – High GI. – raises blood sugar levels dramatically.
  • 69-56 – Medium GI – raises blood sugar levels moderately.
  • 55 or less – Low GI. – raises blood sugar levels slightly.

It can be quite a shock to discover which of our standard foods fit into which category. We are used to being told to eat complex carbohydrates because they digest slowly and cause less sudden raises in BG than their ‘simple carb’ cousins.

Imagine the shock of the folk who tested that favourite US breakfast item, the common bagel, and found it outdid glucose, with a GI of 105!

I must add a note here to the effect that baked goods do differ from place to place and the GI of a bagel has been averaged at around 72 – still high but not off the scale.

A short example of the GI of foods is as follows:-

High GI foods:

  • White and wholemeal bread
  • Certain vegetables and fruit, eg. Beetroots, parsnips, potatoes, dates.
  • Pure fruit juices
  • Highly refined breakfast cereals
  • Rice.

Medium GI foods:

  • Oatmeal, digestive or shortbread biscuits.
  • Some fresh fruits like bananas, cherries & apricots, also many canned fruits like peaches and apricots.
  • Sweetened full fat condensed milk
  • Honey

Low GI foods:

  • Some fruit eg. apples, grapefruit, oranges, peaches, pears.
  • Certain vegetables eg. sweet potato, sweetcorn, peas, chick peas,
  • Assorted beans and legumes eg. butter beans, kidney beans, baked beans, lentils,
  • Grains eg. barley, bulgar wheat, Basmati rice, porridge oats, muesli.

Now I have your interest and you are wondering about the GI of the foods you eat and how to find this out?There are a number of books written which give you lists of foods and their GI.

Examples you could try are:

  1. The New Glucose Revolution Shoppers’ Guide to GI Values 2006: The Authoritative Source of Glycemic Index Values for More Than 500 Foods. By Jennie Brand-Miller & Kaye Foster-Powell.
  2. The New Glucose Revolution Low GI Guide to Diabetes: The Only Authoritative Guide to Managing Diabetes Using the Glycemic Index, by Jennie Brand-Miller.
  3. The G-index Diet: The Missing Link That Makes Permanent Weight Loss Possible Author: Richard N. Podell
  4. The Glucose Revolution: Pocket Guide to the Top 100 Low Glycemic Foods Author: Richard N. Podell

There are also Glycaemic Index tables available on the web.

What you should eat.

At first glance it would appear that the right approach would be to live on foods with a low GI. However high-glycaemic foods are not all ‘bad’ and low-glycaemic foods are not all ‘good’, if one takes general nutrition into consideration.

What I am trying to say is don’t judge a food only by its GI value – it doesn’t tell you everything about what a food has to offer. Living on chocolate may sound great and after all it has a low GI but it also has around 5 calories (kilojoules) per gram and would not be the food of choice for anyone trying to lose weight, to say nothing of leading a healthy lifestyle!

Fruits and vegetables can have higher GI values than some cakes, so why don’t we just, as Marie Antoinette suggested, eat cake? We need the fruit and vegetables because they contain essential nutrients and anti-oxidants while cakes just have calories!

So like all other diets calories (kilojoules) have to be taken into consideration, along with portions and lifestyle. Remember the GI was worked out on 50 grams of a food. If the portion of food you eat is too large you will still gain weight, no matter how low the GI is.

You need to eat a mixture of foods. Just eating low GI foods will become boring with time and is not necessary. Add some moderate or high GI foods and balance them with low GI ones and a little fat or protein.

To make you feel better about this be aware that having protein, fat or a low GI food along with a high GI food will lower the overall GI of that meal.

Remember also that cooking and processing, which break down the food and thus make it easier to absorb, raise the GI. Eat as many of your foods such as fruit and vegetables raw.


  • You are able to eat a wide variety of foods.
  • Low GI foods help you to lose weight.
  • You tend to lose the craving for carbs and feel fuller longer.
  • A lower glycemic response means a lower insulin demand, resulting in better long-term blood glucose control and a reduction in blood lipids.


  1. The GI of foods can vary depending on factors such as ripeness (an unripe banana may have a GI of 30 while a ripe banana has a GI of 52), how it is cooked, it’s variety and where it comes from eg. Potatoes from the USA have been found to have lower GI than those from Australia.
  2. The index is an average and people are all different. The GI of a food can affect one differently at different times.
  3. Using the GI for meal planning is a fairly complicated process It is difficult to accurately work out the GI of a mixed meal.
  4. The index does not take into account the effect on blood sugars after 3 hours and some carbohydrates can take up to 5 hours to digest.
  5. The GI value for some foods isn’t known.

This is a very complex diet to explain.