Week old leftovers are safe to eat as long as the leftover food has been refrigerated.
If the week old leftovers smell good, taste good and has no mold on the week old leftovers then they are safe to eat.
Leftover food is best eaten within a day or two of refrigerating it though.
But it's safe to consume week old leftovers that have been refrigerated.
If the food was leftover and left out overnight then it may be bad depending on what type of food it is.
But if it's been refrigerated or frozen for that week then those leftovers are safe to eat.
Frozen leftovers are safe to eat for up to a year or more depending on what type of food it is.
I've eaten week old leftovers a lot of times and it's never made me sick.