Maximum results? As low carb as you’re willing to go. But ultimately IF is about the timing of what you’re eating, not the content of what you’re eating. You can do well to shed pounds eating any way you see fit. But the best health outcomes will be with a keto-style food intake, whether heavily plant-based or animal-based keto.
The lower carb you go, the easier IF gets. Then you can join the dark side over at r/fasting and try your hand at EF (extended fasts). Good luck and read the FAQs!
Can’t go wrong with meat and vegetables. If you’re currently a heavy person, I’d advise only non-starchy veg, completely avoiding all potatoes, rice, and all grains. Also, don’t drink any calories. Do that and you are golden!!
For lunch I eat steel cut oats with nuts and fruits or a black bean tofu hash with cheese and ranchero sauce.
For dinner I’ll eat your standard meat, carb, vegatable. I try to do better and stick to minimal process foods. So when we had tacos, but kids had shells, I made Spanish quinoa and had a bowl.