Make a reason compelling

I am wondering how can I make my reason compelling enough when it is not. I am fasting and my reasons for fasting are 1) having a better body composition and 2) becoming able to manage my mind in front of the storm of thoughts creating doubt and discomfort. When I fast these reasons seem to not be compelling enough.

My brain finds room to say, “Why are you doing it?” This makes me end up in a rabbit hole of resistance to me doing it. Now the alternatives would be to just stop doing it, simply witnessing that my reasons are not compelling enough, or try to use it as an exercise to see if I can create compelling reasons on purpose. I am not sure how to approach this. Suggestions?