My first fast, the hunger 'spikes' were extremely painful. If 'broken leg' is a 10, the pain would be was a 6 to 9. Intermittently. Around every two hours, for a dozen minutes, from the end of the first day until the end of the second.
I was prepared. A doctor was consulted before, my sister was around, I took the week off, and yes, I entered ketosis 2 days before the fast. Still, it was very difficult.
It did help a ton though, because like my parent say, once you've gone hungry once and managed it fine ( day 3-4-5 were 'normal' to me), your body learn to accept hunger.
I now leave every meal hungry, and it's fine. I went from 34 BMI to 28 in less than two years, without changing anything other than the quantities I ate. The 28 to 25 took 5 years and physical exercise.