As a former wrestler, I have had very similar experiences. On days where I could drink water, I assessed no difference in my productivity between days that I fasted and days that I ate, except when my fasting lasted over three days. Even then, my decline in productivity in relation to the duration with my fasting was not very steep.

However, I found that my productivity is very strongly correlated with my hydration, and going an entire day without water showed immediate, significant, and negative effects. I strove to manage my time in such a way to get all my work done without needing to spend those days programming.