To lose weight, you must minimize calories to create a calorie deficit, regardless of nutrients.  But to be healthy, you need to eat a nutritious diet.  When trying to lose weight, it is a good idea to take a multivitamin/mineral supplement with 100% of the RDA.  Also make sure that you meet your requirement for protein over the course of the day.  But don't worry about potassium until you read this past Ask Mary Q+A, Why is it so hard to get potassium?