The greatest magic for this is exercise and eating healthy.
Weight Loss spells do not actually make you lose weight. Instead, these spells may help attribute to your goal with encouraging you or inducing a placebo effect. Losing weight wont happen overnight regardless (you lose maybe 2 pounds from water loss). You must do the effort, but the spell can aid & push you. Spells can put you in the mindset of things; much like meditation. Love light.