Insulin dose adjustment with food: glycaemic index (GI)

David Kinshuck


Why test glucose levels and adjust insulin dose?

Food good control insulin dose has to matches carbohydrate intake. Starch and sugars (carbohydrates) are the foods that cause blood glucose to rise, and these are the main foods that you need to consider when adjusting quick-acting insulin dose.


Food types

Food contains a mixture of fat, protein, carbohydrate and fibre:


food group examples
protein meat, nuts, fish, cheese,
fat butter, margarine, oil, cream, mayonnaise
carbohydrate bread, rice, pasta, breakfast cereals, milk, fruit, sugar
carbohydrate with protein etc pulses (lentils/beans etc)


Fibre, fat, protein

Fibre (most vegetables) has no calories and so a negligible effect on blood glucose. Fat and protein have a small effect, although this can be significant on occasions (for instance if large amounts are eaten). We can ignore their effect at this stage; it is covered in more detail on the DAFNE course, and patients can work out the effect themselves by regular glucose testing.



Carbohydrate is the main food group that causes a rise in blood glucose, and the does of insulin should match the amount of carbohydrate eaten. Unless the insulin dose and blood insulin level dose match the blood glucose level, the diabetes will not be controlled.

Foods that contain carbohydrates need to be matched accurately with quick-acting insulin if you are to achieve good glucose control. You can eat as little or as much carbohydrate as you want, as long as it is matched by quick-acting insulin (although large amounts will increase weight!):


food containing carbohydrate
cereals fruit & vegetables dairy produce
  • bread / chapattis / naan
  • rice
  • pasta
  • breakfast cereals
  • noodles
  • flour
  • biscuits / crackers
  • pastry / scones
  • cakes / teacakes
  • yorkshire pudding
  • pancakes
  • potato
  • crisps / waffles / chips
  • fruit
  • fruit juice
  • beans / pulses / lentils
  • milk
  • yogurt
  • ice-cream


The carbohydrate portion

Good diabetic control involves eating the amount of carbohydrate you would like, and learning how to match this with an appropriate dose on insulin. Carbohydrate portions (CPs) are a way of judging the amount of carbohydrate in food.

One carbohydrate portions (CP) contains about 10g of carbohydrate.

By using the carbohydrate portion list as here  you will be able to add up the carbohydrate value of the foods you would like to eat. You can then inject the right amount of quick-acting insulin to match this. On the DAFNE training program, you will begin to learn how many units of quick-acting insulin you need for each 1 CP. Carbohydrate in both meals and snakes will need insulin.


An example of Carbohydrate counting (thanks to colleagues at Good Hope)


Meal plan for a type 1 patients with a ratio

  • 1.2u : 10g at breakfast
  • 0.8u : 10g at lunch
  • 0.8u : 10g at evening meal
Meal food / drink weight (g) CHO estimate (g) insulin units
  • 2 x weetabix
  • semiskimmed milk
  • orange juice
  • 38
  • 100
  • 160ml
  • 28
  • 45
  • 14
5.65 (5-6)
  • McDonalds Meal
  • Big mac
  • medium fires
  • medium diet coke
  • -
  • 41
  • 42
  • -
6.64 (6-7)
evening meal
  • cicken curry
  • white basmati rice
  • apple juice
  • 365
  • 161
  • 160ml
  • 57 (combined)
  • 16
5.84 (5-6)
  • 1 pear
  • 2 rich tea biscuits
  • 104
  • 100
  • 10
  • 10
  • 1
  • 1



Different types of carbohydrate and their effect on glucose levels

Sometimes glucose levels rise or lower unpredictably. It is not just the amount of carbohydrate, but also the type that affects blood glucose levels.

Different starches are absorbed at different rates.

You need to experiment with different foods to see how they affect you. Blood glucose monitoring is the main way to find this out.


Glycaemic index (GI): how different foods affect blood glucose levels

graph of glycaemic index (glycemic)

Food with a high glycaemic index GI (red) cause a dramatic rise in blood glucose. Lower glycaemic foods are healthier (green)



The speed of glucose rises and falls after eating a particular food is known as the 'glycaemic index' of that food. Many foods have been tested, although sometimes values change from day to day in the same person...so glycaemic index is only a rough guide.

A carbohydrate that causes a fast rise and fall in blood glucose (i.e. quickly absorbed) has a high glycaemic index; one that is absorbed more slowly has a low glycaemic index. But as the speed of absorption is affected by other foods eaten at the same time, the glycaemic index of carbohydrates becomes important mainly if a single carbohydrate type is eaten in a large amount or on its own.

Low glycaemic index (GI) foods assist diabetic control, high GI foods make good control difficult to achieve. High


High glycaemic foods

high glycaemic index foods
(rapid-acting carbohydrate)
  • glucose
  • Lucozade
  • Cola
  • Jellied sweets
  • Boiled sweets
  • Dextrose tablets
  • Fruit juice



High glycaemic index foods (rapid-acting carbohydrate) are good for treating hypoglycaemia.

Generally high glycaemic foods cause such high glucose spikes, even with the 'correct' dose of insulin These the high levels are dangerous in the long term, and contriubte to diabetic complications, so these food are best avoided as part of the day to day diet..

Low glycaemic foods

low glycaemic index foods (slow-acting carbohydrate)
  • lentils, beans,
  • pulses of all types
  • barley
  • cherries
  • grapefruit
  • nuts
  • fructose

Low glycaemic index foods are absorbed very slowly and if you inject insulin to match carbohydrate you may find the insulin works too quickly. Your blood glucose levels could fall before the carbohydrate is absorbed. It is therefore best to ignore their carbohydrate content and not give any insulin, or if eating large quantities of these foods, give less insulin that would be anticipated from their carbohydrate content.

All other carbohydrate foods can be matched with Quick-Acting insulin, e.g. chocolate, bread, milk, fruit, cereal.


How can I prevent weight gain?

Foods that contain fat provide many more calories than carbohydrates. For example, one potato contains 70Kcal but a portion of chips contains 200Kcal. Alcohol also provides many carbohydrates. See  A dietician can provide individual advice, but healthy eating and physical activity help you to lose weight.


Sweeteners and sugar substitutes

Many foods contain sugar, sugar substitutes, or sweeteners, and each has a different effect on weight and blood glucose.


This causes blood glucose to rise, and contains calories. If eaten on its own, it can lead to erratic blood glucose readings. If the sugar is contained in a recipe then its effect on blood glucose is slowed down. All sugar needs to be covered with quick-acting insulin.


Sugar substitutes (sorbitol, fructose, maltitol, and isomalt)

This do not cause rise in blood glucose levels and so do not need insulin. For this reason they are used in many 'diabetic' products. Unfortunately, they have a laxative effect, and are very expensive. Although they are sugar free, they still contain calories, and can produce gain in weight. These products are not recommend....we recommend you use ordinary products (e.g. chocolates) and inject an appropriate amount of quick-acting insulin.


Arificial sweeteners (aspartamine, Sucralose, Saccharin)

These contain no calories and should have no effect on blood glucose. They are found in soft drinks. Unfortunately new evidence suggests they do not stop people being 'hungry' so they may end up having more calories from other sources.