Best work out routine?

Recently I started using a bowflex to work out 4–5 times a week. I have already seen a result as I have been doing it for over a month. However I was told not to work out everyday but instead work out and take a day off then work out etc. Also every now and then I should take a few days off to let my muscles repair themselves. Is this true? Also what other advice do you have? I am very serious about this and want to make sure I am being effective. I have not changed my eating habits, which usually consist of late night meals and occasionally fast food. Is this really a huge contridiction to working out. I have a fast metabolism so I don’t think it is a huge deal. I know diet is just as important to fitness, but Is it okay for me to eat this way as well ?