Eating foods that have a low score on the glycaemic index can keep blood sugar levels steady and can even help your body metabolise fat more efficiently. Nutritionist Jo Lewin explains how the diet works...
The glycaemic index (GI) was originally designed for people with diabetes to help keep their blood sugar levels under control. It is also a useful tool for non-diabetics in planning healthy meals and choosing foods.
The GI ranks carbohydrate foods based on the rate at which they are broken down into glucose. Too much glucose in the bloodstream triggers the pancreas to release a hormone called insulin to bring blood sugar levels back into the normal range. Consuming foods with a high-GI leads to high levels of circulating insulin levels, which we want to avoid.
How does it work?
Carbohydrates are found in starchy foods such as bread, pasta, potatoes and in sugary foods such as fruit, cakes, biscuits and honey. They provide the main source of energy, used to fuel every part of the body from the brain to our beating hearts (a bit like petrol in a car). All carbohydrates have the ability to raise glucose levels in the blood but the slower a carbohydrate is digested, the slower it releases energy - in the form of glucose - into the bloodstream and the lower its GI score. The faster a carbohydrate is digested, the more rapidly glucose levels in the blood rise, and the higher the GI score.
The speed at which this digestion to glucose occurs, and the amount it raises glucose levels in the blood is measured on the GI scale. Glucose, one of the most rapidly absorbed carbohydrates, has been given a score of 100.
A sharp increase in glucose in the blood triggers the pancreas to release a rush of the hormone insulin, which removes any excess glucose. Insulin removes the surplus glucose from the blood and lowers the speed at which the body burns fat. A large surge in insulin, caused by eating high-GI foods, will start reactions in the body that leave you feeling lethargic, hungry and craving more sugar.
Eating low-GI carbohydrate foods causes a steady rise in the level of glucose in the blood, which in turn leads to a small and gentle rise in insulin. Small increases in insulin keep you feeling full and energised for hours after eating and also encourage the body to burn fat.
Foods with a GI of 70 or more are typically called 'high-GI foods' as they trigger a rapid rise in blood sugar. Foods with a GI of 55-69 are 'medium-GI foods' as they trigger a moderate increase. Foods with a GI below 55 are 'low-GI foods' because they have a minor impact on blood sugar.
- Low-GI foods provide natural, slowly released energy.
- Generally, the less processed a carbohydrate, the more likely it is to have a low-GI score.
- Foods that are white, including processed foods made with white flour and white sugar, tend to have a high-GI.
- High fibre foods take longer to digest and therefore produce a slower rise in blood sugar levels. Fibre also keeps you feeling fuller for longer, which helps prevent overeating. Most vegetables, whole-grains, legumes, nuts, seeds and fruits are rich in fibre when you eat them whole.
Your glycaemic response to a food also depends on the other foods you eat with it. You can eat healthy high-GI foods in a meal that also contains protein and essential fats. Combining foods slows down the rate at which your body releases sugar from a meal.
For example, try a high-GI baked potato with low-fat cheese (protein) and a green salad (fibre), or a higher GI carrot soup, sprinkled with seeds (essential fats) and wholegrain pitta (fibre) stuffed with lean chicken (protein). That way you get the nutrients from healthy, high-GI foods while minimising the effect on your blood sugar.
Lower GI foods
Higher GI foods
|Pitta bread||White bread|
|Fresh apricots||Baguettes and bagels|
|Under-ripe bananas||Apricot puree make with sugar|
|Plain yogurt with fresh berries||Cupcakes|
|Spaghetti||Fruit flavoured yogurts|
|Fructose||Canned grapefruit in syrup|
|Fresh tomato salsa||Mashed potatoes|
|70% dark chocolate||Tomato ketchup|
|Tortilla wraps||Chocolate biscuits|
Eating out or with friends can be difficult if you are following a low-GI diet. Limit any potential damage by remembering a few tricks. Opt for multigrain, sourdough or granary bread and say no to chunks of baguette and ciabatta. Decline chips and have an extra serving of low-GI vegetables or salad instead. Skip pudding or compromise by having a small amount. If drinking alcohol, consume with meals and try 70% cocoa chocolate to satisfy a chocolate craving or try spreading high-GI white bread with a protein-rich topping such as peanut butter to slow digestion and limit the overall effect on blood sugar levels. Added sugar affects the GI rating. This means that canned fruit in syrup has a higher GI than canned fruit in juice.
As tropical fruits have a moderately high-GI score, try citrus, stone fruits and apples, pears, berries and rhubarb:
Apple, pear & cherry compote
10-minute winter fruit compote
Grapefruit, orange & apricot salad
Try making your own wholemeal bread:
Mixed seed bread
Jo Lewin holds a degree in nutritional therapy and works as a community health nutritionist and private consultant. She is an accredited member of BANT, covered by the association's code of ethics and practice.
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