Get some exercise and eat healthy whenever you have control over the meals.

On my trips, I try to find at least 1 night where I'm chilling out, going for a long(ish) run, and eating light. (Usually sashimi.) There's guaranteed to be other nights with client/colleague dinners - those are long, heavy meals and booze-fueled late nights. The solo night is needed to cleanse from all of that crap.

Customs are different around the world, but I've never encountered a sushi bar that wasn't welcoming to a solo diner. So depending on where you travel, you might begin to experiment with sushi if you aren't into it already.

Hotel bars are the other domain of the solo diner, but the food is often crazy-salty and frankly uninspiring. Of course some cities have a good streetfood scene...quality may vary.