Suhur is the food or drink taken by the person who intends to fast in the last one sixth of the night before dawn which is called Sahar. It is highly recommended to have Suhur even very little or just water, but having Suhur is never obligatory in any type of fasting even in the month of Ramadhan. Suhur has nothing to do with the validity of any type of fasting.
Wassalam.