Can i loss weight by just being on GI diet ?

Fad diets, regardless of what type they are will reduce your weight if you combine it with exercise or are eating few calories than you burn. Unfortunately once you stop the diet and return to your previous eating regime then the weight will return, often people end up heavier than they were before they started and the issues start again.
If you yo-yo diet then the body's systems will go into helter-skelter mode and your metabolism will be knocked out meaning that you burn your food energy at a lower rate, hence the increasing weight.
Applying the principles of low GI or low GL diets (see Patrick Holford's excellent GL diet book) to your everyday life, combined with portion control will give you the tools to reduce your weight safely and ensure that your weight will stay at its natural state consistently.
Think the 80:20 rule: 80% good, 20% naughty.
Good luck.

Thank you all for the answers :-) will try to keep my diet balanced.

You can lose weight on any diet that restricts calorie intake but you have to look at how you live your life and whether such a diet can fit into your daily lifestyle. By far the best way to lose weight is to modify your eating habits; moderation is the key. Combined with regular physical exercise.
All the best, if you need any further information or advice please do contact me.
Richard

no, unfortunately you can't. If you do that your body will adapt to the new diet. The best thing to lose weight is combine physical exercise with a good diet.
Please do not hesitate to contact me for further details
All the best
Luiz Colturato
07737417374