Have you ever really thought about what effect the foods you eat have on your blood sugar levels? Do you ever remember feeling sleepy after your lunchtime baguette, or feeling like your tank is empty whilst training? Looking at what you eat and when you eat it could help prevent such issues. Ever heard of the Glycaemic Index (GI) and wondered what it’s all about? Well, here’s the lowdown.

To describe more accurately the effect different foods have on your blood sugar levels, scientists developed the Glycaemic Index (GI). It is a ranking of foods from 0 to 100 based on their immediate effect on blood sugar levels, a measure of the speed at which you digest food and convert it into glucose. The faster the rise in blood glucose, the higher the rating on the index. The GI of foods is very useful to know as it tells you how the body responds to them. If you need to get carbohydrates into your bloodstream and muscle cells quickly, for example immediately after exercise to kick start glycogen replacement, you would choose high GI foods.

The GI of a food is worked out by the amount of food containing 50g of carbohydrate. For example, to test baked potatoes you would eat 250g potatoes, which contain 50g carbohydrate. Over the next couple of hours a sample of blood is taken every 15 minutes and the blood sugar level measured. These figures are then plotted on a graph via a PC programme and compared with the reference food (glucose)and a GI figure for the food is then given. The GI of baked potatoes is 85, which means that eating baked potatoes produces a rise in blood sugar which is 85% as great as that produced after eating an equivalent amount of glucose.

The GI of more than 600 foods is known so for me to list them all would take forever, however I have listed a few below. Even the GI values of the food may differ slightly on the various GI tables available, but the food type should still be within the same GI category (low, medium or high).

Most values lie somewhere between 20 and 100 and most people find it more useful to classify foods as High GI (60-100), medium GI (40-59) and low GI (less than 40). This simply makes it easier to select the appropriate food before, during and after exercise.

In a nutshell, the higher the GI the higher the blood sugar levels after eating that food. In general, refined starchy foods including potatoes, white rice and white bread, as well as sugary foods such as soft drinks and biscuits are high on the glycaemic index. For example, baked potatoes (GI 85) and white rice (GI 87) produce a rise in blood sugar almost the same as eating pure glucose!! Less refined starchy foods like porridge, beans, lentils, muesli, as well as fruit and dairy products are lower on the glycaemic index. They produce a much smaller rise in blood sugar compared with glucose.

The effect on blood glucose from a high versus low glycemic index carbohydrate

Foods only appear on the GI index if they contain carbohydrate. This explains why you won’t find foods like fresh meat, chicken, fish, eggs and cheese in GI lists. However, you may find some processed foods like sausages or chicken nuggets in a GI list because they contain flour!

Low Glycaemic Index foods (55 or less)
Include some of these foods in each meal or snack, but go for low-fat choices where possible, such as skimmed milk. If you want to lose weight, you’ll also need to watch your portion sizes. That means sticking to small servings of pasta and noodles, limiting yourself to two slices of bread with a meal, and having only a couple of squares of chocolate or a small handful of peanuts!

Low GI Foods

Roasted and salted peanuts-14
Low-fat yoghurt with sweetener-14
Cherries-22
Grapefruit-25
Pearl barley-25
Red lentils-26
Whole milk-27
Dried apricots-31
Butter beans-31
Fettucine pasta-32
Skimmed milk-32
Low-fat fruit yoghurt-33
Wholemeal spaghetti-37
Apples-38
Pears-38
Tomato soup, canned-38
Apple juice, unsweetened-40
Noodles-40
White spaghetti-41
All Bran-42
Chick peas, canned-42
Peaches-42
Porridge made with water-42
Lentil soup-44
Oranges-44
Macaroni-45
Green grapes-46
Orange juice-46
Peas-48
Baked beans in tomato sauce-48
Carrots, boiled-49
Milk chocolate-49
Kiwi fruit-52
Stoneground wholemeal bread-53
Crisps-54
Special K-54
Banana-55
Raw oatbran-55
Sweetcorn-55

Medium Glycaemic Index foods (56 to 69)
You may include a few of these foods each day, but again limit portion sizes if you want to lose weight.
Moderate GI Foods

Muesli, non toasted-56
Boiled potatoes-56
Sultanas-56
Pitta bread-57
Basmati Rice-58
Honey-58
Digestive biscuit-59
Cheese and tomato pizza-60
Ice cream-61
New potatoes-62
Coca cola-63
Apricots, canned in syrup-64
Raisins-64
Shortbread biscuit-64
Couscous-65
Rye bread-65
Pineapple, fresh-66
Cantaloupe melon-67
Croissant-67
Shredded wheat-67
Mars bar-68
Ryvita-69
Crumpet, toasted-69
Weetabix-69
Wholemeal bread-69

High Glycaemic Index foods (70 or more)
Swap these foods for those with a low GI value or eat them together with a low GI food. Having a jacket potato with baked beans, for example, will lower the GI value of that whole meal.

High GI Foods

Mashed potato-70
White bread-70
Watermelon-72
Swede-72
Bagel-72
Branflakes-74
Cheerios-74
French fries-75
Coco Pops-77
Jelly beans-80
Rice cakes-82
Rice Krispies-82
Cornflakes-82
Jacket potato-85
Puffed wheat-89
Baguette-95
Parsnips, boiled-97
White rice, steamed-98

Next time we’ll have a look at how the GI can help your performance.

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