All foods that we eat contain energy and the amount of energy they contain and which is available to us is based on their composition and structure. The main components of foods are fat, protein, available carbohydrates, and/or fibre.
Foods which are mainly composed of fat, protein, available carbohydrates, and/or fibre, are more slowly broken down and give a sustained release of energy. However foods which contain a high sugar and/or carbohydrate that is readily digested are quickly broken down meaning that energy is rapidly available.
Glycaemic Response focuses on how quickly carbohydrate-rich foods are broken down in the gut and how quickly the energy from the carbohydrates present in these foods is released into the body’s blood stream as blood glucose for use throughout the whole body. How quickly this happens can be categorised by measurements of the body’s blood glucose levels.
Relative values for energy release to the body as blood glucose are determined using scientific tests which measure the effect of foods on blood glucose compared with the effect of glucose references.
The following information explains the different measures:
Glycaemic Index (GI)
The Glycaemic Index (GI) ranks carbohydrate-rich foods based on the effect that the carbohydrate present in the food has on blood glucose levels when consumed at equal carbohydrate intakes in the food.
The problem with GI is that although it is determined from measurements of blood glucose responses to the whole foods, the responses are attributed to the carbohydrate component of the food alone. GI is calculated as the response to a portion of food containing 50 g carbohydrate as a percentage of the response to 50 g glucose, so it allows you to compare carbohydrates in foods, and foods that contain equal amounts of carbohydrates.
However, not all foods or food portions contain the same quantity of carbohydrate so it makes comparisons between foods difficult. Also the GI of food does not change with quantity, so a muesli bar has a GI of 50 whether a person consumes 50 g or 80 g, meaning that the effect of serving size is neglected.
Glycaemic Load (GL)
Glycaemic Load is a new measure for assisting in making healthy food choices by being able to compare foods using a combination of the Glycaemic Index of the food and the amount of carbohydrate in the food. This measure gives an estimate of the relative glycaemic effect a food has on blood glucose expressed as Glycaemic Glucose Equivalents (GGE). If a portion of food has a GGE value of 8, it means it would have about the same effect on blood glucose as 8 g of glucose.
The following example explains how GL is more accurate than GI when presented with foods of different serve sizes and carbohydrate content. An average 58 g apricot and a 128 g banana have Glycaemic Indexes of 57 and 58 respectively. However, because a banana contains more carbohydrate and is twice the size of the apricot it will raise blood glucose levels six times higher than an apricot. This real difference in the glycaemic effects of a banana versus an apricot is reflected in their GL values; the GL of the 58 g apricot is 3, while the GL of the banana is 18. Hence the GL gives a better indication of the impact of the food item on blood glucose levels.
There are three categories of GL which foods can be classified into and a balanced diet should contain foods from all of these.
Low GL, but high carbohydrate foods assist in making you feel fuller for longer due to a lower and more sustained increase in blood glucose levels. This assists in controlling weight by making you feel less like snacking between meals. Including carbohydrate foods in the diet that give low blood glucose responses improves insulin sensitivity and decreases the risk of diabetes. Low GL foods are classified as containing 0 to 10 GGE/100g and examples are Multigrain bread (5), WeetBix (7) and raw apple (5).
Medium GL foods range from 11 to 19 GGE/100g and examples are Bread (Fibre white) (10), Molenberg Bread (10) and fresh orange juice (12).
High GL foods contain 20 GGE/100g or higher and examples are plain bagel (25), toasted sweetened muesli (25), and canned apricots (47). Diets containing large amounts of high-GL food have been associated with increased risk of diabetes and heart disease. For people with Type 2 diabetes, consuming a low-GL diet is one method of controlling their diabetes and general health as low-GL foods put less pressure on the requirements for insulin.
However an example of how low GL and high GL foods are an important part of a person’s diet is when you consider the requirements of a sports person. Sports people consume low-GL foods before an event to delay the time it takes to reach exhaustion point. However they also consume high-GL foods to reduce fatigue during an event and to help with recovery time afterwards.
Glycaemic Load offers a guide to choosing a variety of food combinations to make up a balanced diet and give a measure of the relative impact the food will have on blood glucose levels.