Well the body requires that you have X amount of these vitamins/minerals in your system and as such if you have a poor diet, you wont have near what you require. As far as switching to greens and doing away with a multi, I would have to disagree. A multi allows you to intake certain nutrients in proper ratios to fuel your body along. If you are a very athletic person or someone looking for an edge on their diet, I do suggest incorporating a good greens blend in with the multi. Suggestions: Nature's Plus' Source of Life: Green Lightning, or Sunny Green's Veggie Complete, both are excellent and cover not only conventional greens, but chorella, spirulina, barley, wheatgrass, kelp, and in the case of the Green Lightning, bee pollen for a immune and energy boost.