Take a careful look at your reservation on-line. No food in Y doesn't always mean no food in F. Just below the departure city of each flight, it should give you a meal status (in very tiny print). If you were flying in Y on one of these flights, it might say:
Class: Economy (B) Meal: None.
And if you got the upgrade and a meal is offered in F, then it would say:
Class: First (R) Meal: Snack. No Special Meal Offered.