The Glycemic Index can be a helpful tool for weight loss. However, it's also important to realize its limitations.
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 low-GI foods therefore helps you to feel fuller for longer, which means you can eat less.
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.
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.