Por. Para would be used to say that something was made *for* someone.
A ellas le gustaban cocinar.
A ellas tenían el costumbre de desayunar juntas los sábados.
Answer:
Sugar and fast food are a few bad things for your hair, that should be avoided at all times.
Explanation:
Mateo y yo <u><em>prefiero</em></u> los libros de Lord of the Rings en vez de los de Harry Potter.