These diet spells all focus on diets, whether it is a diet to gain weight or lose weight these spells will help.
Diet spells walk a fine line in the difficulty and consequences of casting. They are rather simple and easy to cast and the consequences of miscast spells are usually nothing to big.
However, these are spells dealing with your body, or at least the body of whoever the target of the spell is. As such they do carry with them enormous powers.