there's always room for dessert
Proverb used when someone claims to be full but still has appetite for sweets. Literally 'sweet things go in a separate stomach'.
Even after saying 'I'm full,' when she saw the cake she said 'there's always room for dessert' and started eating.
A common Japanese proverb. The exact origin is uncertain, but it reflects the cultural notion that sweets are enjoyed separately from a main meal.