There are some reasons why a low GI diet can contribute to weight loss. For example, many low GI foods are bulky, high in fiber, and more satiating than high GI foods because they take longer for the body to process; e.g. legumes take longer to process than bread. Consuming these foods therefore helps people to feel fuller for longer and means they are less likely to overindulge. Low GI foods also produce less insulin, and low insulin levels help people to burn fat instead of carbohydrate.

However, following a low GI or GL diet does not automatically mean that you will lose weight. These indexes only measure the carbohydrate content of foods and do not account for calories, fat, and other nutrients. It is vital to consider overall calorie and fat intake, as well as carbohydrate intake, for effective weight management. It is also easy to make unhealthy choices based on GI or GL rating alone. For example, chocolate has a low GI compared to a slice of white bread, but bread has more nutrients and less calories and fat than chocolate, and is therefore a much better option.

According to Jennie Brand-Miller, Professor of Human Nutrition at the University of Sydney and a leading researcher in the development of the GI, the GI/GL is essentially about making smart carbohydrate choices and should be thought about in terms of swaps: "People should not think that chocolate is a good swap for watermelon!" she warns.

Portion control also remains vital for weight loss when using the GI or GL. A low GI or GL rating should never suggest free reign on portion sizes. This is as important to those who are controlling their blood sugar levels as it is to those who are controlling their weight.

It is good to keep in mind that GI and GL are really research tools for analyzing carbohydrates in foods. Calculating the GI or GL of every food before you eat it is neither practical nor sensible. However, being familiar with the GI/GL rating of foods can help you improve the quality of your carbohydrate choices, whether for insulin moderation or weight loss purposes.

People who have diabetes do not produce enough insulin in their bodies to effectively manage glucose and maintain their blood sugar levels. Consequently, it is very important for people with diabetes to manage their glucose intake carefully. Low GI and GL diets are believed to be helpful to people with diabetes because low GI and GL foods release glucose into the bloodstream slowly and more evenly than high GI and GL foods, making glucose levels easier to regulate.

Brand-Miller says that "choosing low GI sources of carbohydrate is a natural way of keeping blood glucose levels on an even keel, which helps people avoid marked fluctuations." However, the GI or GL should clearly not be the only point of reference in managing carbohydrate intake; instead they should be used as tools.

A low GI diet may also help to prevent Type 2 diabetes. A report on GI, GL, and the risk of Type 2 diabetes in the American Journal of Clinical Nutrition (July, 2002) found that diets high in both high glycemic index and high glycemic load foods have been associated with a greater risk of type 2 diabetes in both men and women.

Researchers agree that larger studies and clinical trials are needed to definitively answer the question of whether there is a link between a diet of high GI foods and the development of diabetes. But as it stands, the current research gives a fairly strong indication that a low GI/GL diet is a wise choice for both managing and preventing diabetes.