GI approach to weight control
Published by Bupa's health information team, healthinfo@bupa.com, April 2008
This article looks at the glycaemic index (GI) approach to weight management. The GI concept focuses on the effect that your food has on your blood sugar level and has become popular in recent years.
The GI approach to eating may help you control your weight and may also help reduce the risk of heart disease, diabetes and cancer, although doctors need to do more research in this area before they make new dietary recommendations.
What is the glycaemic index?
The Glycaemic Index (GI) ranks foods according to the effect they have on the blood sugar level (the amount of glucose in the bloodstream).
Scientists developed the system in 1981 while studying the way different carbohydrate-rich foods affect the blood sugar levels of people with diabetes. The researchers found that it was not simply the sugar content of these foods that determined their effect on blood sugar levels. From this research, they developed the GI to categorise the effect of different foods on blood glucose.
Carbohydrates
Carbohydrates provide our main source of energy. They can be single molecules, such as glucose, double molecules, such as sucrose, or chains, such as starch. The body needs to break all carbohydrates down into simple sugars, mainly glucose, for energy. The glucose is absorbed into the blood from the digestive system.
How does the glycaemic index work?
The GI ranges from zero to 100. The higher the GI value of a food, the more rapidly and dramatically it causes your blood sugar to rise.
Most GI lists divide foods into three categories: high (70-100), moderate/medium (55-69) and low (below 55).
How does the GI approach help control weight?
When we eat foods containing carbohydrates, there is a rise in blood glucose after 15-45 minutes. This returns to fasting levels around two or three hours later.
In foods with a high GI, sugar is more easily absorbed into the blood, so they produce a fast and dramatic increase in blood sugar levels, followed by a fast decrease in glucose levels. In contrast, the slow release of sugar into the blood from foods with a low GI value provides a steady, prolonged supply of energy. The theory is that this steadier, more stable supply of energy fills us up for longer and puts us off snacking. This should mean we can eat fewer calories overall and so lose weight.
Factors affecting the GI of foods
Anything that affects the rate at which carbohydrates are broken down into glucose and absorbed into the blood affects the GI of a food. This can include:
- the size of the carbohydrates - short-chain carbohydrates such as sucrose are absorbed more quickly than starchy carbohydrates
- the structure of the carbohydrates - the starchy carbohydrates in bread and pasta are similar sizes but bread has a higher GI because of their structure
- how foods are processed - instant porridge has a higher GI than porridge made with raw rolled oats
- how foods are cooked - mashed potato has a higher GI than boiled new potatoes
- the ripeness of fruit or vegetables - an over-ripe banana has a higher GI value than under-ripe one
- how long you chew your food for - if the food particles are smaller when you swallow the food, the GI is higher
Are there any problems with the GI approach to weight management?
Sticking to low GI foods doesn't necessarily mean that you are following a healthy diet. Many foods that have a low GI value are high in fat, because fat and protein slow down carbohydrate absorption. They can also have high salt and low vitamin and mineral content. For example, sponge cakes and ice cream have a low GI, but are not nutritious snacks. Similarly, watermelon and parsnips have high GI values, but both contain useful vitamins. To compensate for this, most GI diet plans include foods that are nutritious and low on the Glycaemic Index, such as vegetables and nuts.
Another tricky aspect of the GI approach is that you need to bear in mind the overall GI value of a meal, not just individual foods. White bread has a high GI, but if you eat it with a low GI food such as baked beans, the meal takes on a GI value between the two. This means you can lower the overall GI of a meal by including more low GI foods.
Are there any other health benefits to the GI approach?
A low GI diet is good for you if you already have diabetes (type 1 or type 2) because it helps you control your blood sugar more effectively.
Low GI diets have also been linked to other health benefits, including reducing the risk of:
- type 2 diabetes
- heart disease and stroke
- diet-related cancers such as colon and breast cancer
But doctors need to do more research into this to prove the link.
Getting started
If you decide to follow a low GI diet, you still need to make sure you eat a balanced diet. A healthy diet should include plenty of fruit and vegetables, and a minimal amount of fatty or salty foods.
To lose weight on a GI diet you need to make sure your overall calorie intake is lower than the amount you are burning through activity. You will find you lose weight quicker if you exercise as well - aim for 30 minutes of moderate activity on at least five days of the week.
Key points
- The GI of a food tells you what effect that food has on your blood sugar.
- Many factors affect the GI of a food, including the type of carbohydrate it contains, how it's cooked and how long you chew it.
- Low GI foods cause a slower release of sugar into your blood.
- Eating low GI foods can help you to feel full for longer.
- Including lots of low GI foods can mean you eat fewer calories overall.
- Eating a low-GI diet may reduce your risk of diabetes, heart disease and cancer.
Further information
- Food Standards Agency
020 7404 6504
www.eatwell.gov.uk - Beat (formerly the Eating Disorders Association)
www.b-eat.co.uk - Weightwise
www.bdaweightwise.com
Related information
- Healthy weight and exercise
- Carbohydrates
- Benefits of exercise
- Exercise - what type, how much?
- Walking and health
- Football and health
- Cycling and health
