How can I boost my energy, mood, and retention by diet?

Eat sensibly. Avoid the very greasy, sugary and salty stuff, and anything that you know you tend to overeat. Get an interesting and varied diet, and ask your physician whether you might want an economical supplement. Especially, eat with friends who are into fitness and athletics. They're probably the best company and can boost your mood and introduce you to things that'll really help you.