You cant physicaly rid yourself of the extra weight you have through magic alone. Magic can motivate you, make your exercising more effective, ultimately helping you lose weight easier, but it alone cant do the job for you. Its still up to you to make the effort to lose weight, magic can just make it easier.
The 'best' spell to lose weight is something you will create yourself, for example a spell that will give you the strength to need to eat less or something like that.
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