Gluten-free: no; I'm allergic to wheat, so wheat-free, yes. When I eat wheat, I itch all over for days and days, find it more difficult to focus (like having a perpetual brain fog), and am generally more irritable overall. Oh, it also disrupts my ability to fall asleep and to stay asleep. So, wheat and I are not friends.
The greatest advantage I have found about refraining from eating wheat -- aside from being able to get a good night's sleep and not itching all over -- is I have also shed a ton of weight super fast. Twice in the past 7 years I have stopped eating wheat and twice now I've lost a ton of weight. And so long as I abstain from the wheat, the weight stays off.
Dairy-free: no, although I ought to be. It gives me a terrible, upset stomach stomach and bad gas. You'd think that would be incentive enough but I crave the stuff.
Here's one worth considering:
Going Sugar-free: trying! And that includes being free of artificial sugar substitutes, too. We started down this path last January. It is SUPER hard to avoid foods not laced with sugar or sugar substitutes. There are no "diet" foods, either. I cook almost everything from scratch--limited pre-packaged foods, snacks and (sigh) chocolate in moderation.
I don't know if any of these things directly affect my behavior, except that I feel great, I sleep better, and I have a ton more energy, focus, and enthusiasm for the day ahead. Who can go wrong with taking better care of oneself?