It’s still a numbers game, but it’s hard to out-eat your fasting if you’re only eating once a week. Beyond that, I’d say make sure you mix in something healthy to get a good dose of micros during feed and just avoid anything that will cause you to not stick to the routine.
Tbh you seem like a bad candidate for fasting, especially like that. You need to address the underlying issues of addiction, to sugar/carbs, and really get at the why behind it. For me, and most, we tend to “eat our feelings,” to use food for its dopamine inducing qualities.
If you eat one meal a week and it’s full of junk food, honestly you’d probably just feel like garbage. On the other hand, when you fast you crave healthy foods that are actually substantial so if you go in to it trying to improve your diet that may work. Maybe try OMAD and slowly cut the carsb out?