I started watching my diet in my 20s. I started doing so because I didn't want to harm myself long term and I started gaining weight. I still go back to my boxed pasta diet once in a while (I grew up on the stuff! I love it!) and it doesn't effect me in a noticeable way. I'm no longer an athlete though.

Actually that is not true, it does effect my poop. I strongly perfer pooping on a veggie rich diet!

Thankfully getting married has helped my diet. My spouse leaves for work for extended periods sometimes which is when my diet usually slips.