Is boiling cabbage leaves and placing them on the buttocks to absorb fat forbidden (haram) or does it show disdain for God's blessings?

It is permissible to use cabbage or other foods to absorb fats from the body, and there is no disdain for Allah's blessings in that. Allah Almighty created all that is in the earth for humankind to benefit from, and using these foods to absorb fats falls under the permissible utilization for treatment.