Can fasting cause hair loss?

Fasting for 18 hours will not likely cause hair loss.   Long term starvation and malnutrition may cause hair loss. 

No. An 18 hour fast will not cause hair loss. Theoretically a long fast might deplete essential vitamins but taking a daily vitamin pill would eliminate that risk,

For most individuals, the daily supply of sufficient nutrients over a 24 hour period should be sufficient for normal hair growth provided there are no signficant changes in the individual's weight. A small proportion of individuals with underlying significant medical issues could experience a minor shed with caloric restriction over longer periods.

If a person loses a lot of weight in a very short amount of time, it could cause temporary hair loss.  However, fasting is during the day and most people eat more at night to compensate and so do not lose much weight if any.  In that case, it should not effect hair loss.

Any long period of fasting or weight loss can cause hair loss, but from what you are describing with good eating after a daily fast, it should not impact hair growth