It really depends on what you mean...
With a weight loss spell, you cannot create a spell to magickally make your weight disappear. You can do something to help increase your will to do the necessary things for weight loss. You can do a ritual under the idea of making a better view of yourself and your weight so that as you work at weight loss it feels wonderful in more ways than one. But direct weight loss due to a spell is impossible.
And what kinds of death spells? There are spells that deal with summoning or banishing the spirits of the dead. There are spells to use during funerals to help souls pass on, get stuck here, etc. But a spell to stop death is impossible, and one to directly kill another is impossible. You could do something that puts the energy into the world to increase the chances of it happening by a little, itsy, bitsy amount, but nothing you ever do magickally would legitimately kill someone.
Good luck and be safe!