Most places should have some kind of meat and salad dishes. Just avoid junky dressings and sauces. If you were going to cheat, it’d be better to do it with steak than pasta. It could even be a good source of vitamins and protein.
If you eat something beforehand, your hunger won’t be strong enough to temp you into eating junk. If you eat starch or sugar, it’ll be food for candida and pathogens like Klebsiella, and carb cravings will start again and last for at least a day. It’s not really worth it if you can get away with a salad.
Edit: I just noticed you’re in Japan. Maybe steak isn’t so likely. They love adding sugar to absolutely everything. 90% of girls seem to be on diets though, so there must be some salad places about, right?