If you are young and very healthy, sex once a day will not do your body a great deal of harm. But please think that do you really need to do it once a day? Why? Also, will your g/f wants to do it with you once a day? Different people have different needs! Like some people need to drink coffee everyday but others do not. You need to talk to your g/f to see if she is happy to have sex with you everyday!
Doing it once a day will burn up a lot of your energy and will make you weak! So if you are not that strong and healthy, it will cause you health problem in the long run!
May be you are new to sex and find it curious and want to do it everyday but try to cool down and think about life and how to be nice with your g/f. Having sex everyday does not mean that you are being nice to her. You also need to do other things with her to keep her happy so that you two can last for a long time.
What is in your mind.
Sex is both side .
1. It would do you heath harm.
2. What about the other side sex mind.
3. Do this sex or love.
so think about it.