АППЕТИТ ПРИХОДИТ ВО ВРЕМЯ ЕДЫ (saying) your interest in or desire for sth. grows as you practice, experience, or learn it
appetite comes (grows) with eating
= eating and scratching (drinking) want but a beginning.
«Пока чай дойдёт, закусите», - Алферов обвёл рукой стол. «Спасибо, чай попью, а есть не хочу, завтракал». - «Ну, ну, смотрите, а захотите — ешьте, аппетит приходит во время еды» (Рыбаков 2). "Have a bite while the tea is brewing," he (Al-ferov) said, indicating the food. "Thank you, I'll have some tea, but I won't eat. I've already had breakfast," Sasha replied. "Well, just look and if you feel like it, eat something. The appetite grows with eating" (2a).