Glycaemic index/GI

Although the GI system has been around since the 1990's, it has recently gained more acceptance within the diet and health industry. There are an increasing number of diet plans that rely on the GI system. Despite this widespread acceptance the academic applications to everyday life remain flawed and difficult.

Aim to eat a well balanced healthy diet based on a variety of foods. A healthy diet should consist of a mix of carbohydrate rich foods. You should try and increase your intake of low GI foods, such as whole-grain breads, pasta, brown rice, wholegrain breakfast cereals, beans and pulses and fruit and vegetables.

The current system also implies that foods with a high GI have no other nutritional benefits. Bread is a low fat, highly nutritious food packed with B-vitamins, calcium and iron. According to GI tables, food like bread, broad beans, carrots, bananas and most fruits are all high GI foods. On the basis of this one measurement - these foods would be labelled as 'unhealthy' and avoided. In light of the recent Department of Health 5 a day campaign -this would be nutritional disaster. If consumers are still confused about basic weight loss messages can we really expect them to understand the many complexities and flaws of the GI system? We currently need more reliable data and reproducible results before we adopt this system.

The glycaemic index has been criticised on the grounds that values for specific foods are not reproducible from one laboratory to another or in the same individual on different occasions. It has also been suggested that the glycaemic index of a food changes when it is incorporated into meals or diets.

Factors that affect the glycaemic response include particle size, processing, storage, cooking and the presence of fat and protein.  For these and other reasons the GI is not a valid or nutritionally sound tool to use in the formation of diets and eating plans:

1. Generally speaking the smaller the particle size, the greater the glycaemic response. Soda bread scones made from coarsely milled flour produce smaller glucose and insulin responses than scones made from finer flour milled from the same grist.
2. The GI of a food is easily changed by actions such as chewing. The more a food is chewed, the greater the glycaemic response.
3. Similarly the rate of food intake may also play a part with foods consumed quickly initiating a greater GI response than foods consumed slowly.
4. Fat is known to delay digestion and protein is known to increase insulin production. A given amount of fat may produce different responses depending on whether it has been cooked with the carbohydrate or added after cooking as a spread.
5. High carbohydrate foods are not consumed in isolation but as part of a mixed diet. Bread is typically eaten with a filling or topping. Add a slice of cheese to white bread and the GI falls.
6. The cooking and storage of products may affect the GI ranking. When bread cools a starch is produced that is resistant to digestion (resistant starch). Processing can also affect the response as the more highly processed the food is, the higher the GI.