It’s naturally harder to fast when you don’t have much body fat to burn — for understandable reasons, since your body burns fat as fuel starting right around 16 hours of fasting.
What’s the reason you’ve pegged 115 as a goal even though you are already not overweight at 125? Maybe it’s not the right goal for your body. If you’re looking for more muscle definition or to “look better naked”, weight training to build muscle is often more effective than trying to lose more weight when you’re already at a normal weight.
If your goal is weight loss, extending your fasting window won’t make any difference. You will need to consume less calories for that to happen. I have gained weight (purposely) on 20:4 and lost weight on 12:12. It’s all about calories for weight gain or loss.
But to answer your question, if you simply want to extend your fasting window, I would recommend black coffee at the 16 hour mark and consuming more fat during your feeding window. Heavy cream, nuts, Irish butter, etc.
water intake was critical for me. not being too much of a purist, caffeine helped too. or a tiny morsel of something under 50 calories. also might help to take inventory of your routines. if you initially set up your fasting window based on your schedule, there could be that routine of anticipating a meal driving your hanger. what if you started your window earlier rather than trying to extend it at the end? if you must extend it can you add a task to your daily routine to distract yourself longer?
Just because 16:8, 18:6, 20:4, and such are nice round numbers doesn’t mean you can’t work your way up in-between them. It doesn’t all need to be 2 hour chunks only. I spent like 5 months doing 16:8 while occasionally pushing it a few hours longer if I was feeling it that day before doing OMAD somewhat consistently, and I still don’t every day.
Maybe try working on adding just 30 minutes every week.
It’s significantly easier than you think. Personally, if I struggle with hunger or cravings, I drink tea. I bring tea with me to work, and I always have a after on me.
I think it helped me too to consider how obsessed our society has become with food. Our ancestors didn’t go hunter and kill animals three times a day, so why should we fee the need to have three meals a day