You won't get much meat off an ISA brown. Of course you can eat them, you can eat any chicken, but unless you are not so much interested in the meat as in making broth from the carcass, it would make more sense to pick a meatier, more dual-purpose breed. (Sexlinks like ISA browns are not really dual purpose).
Be aware though that dual purpose chickens will not give you anything even vaguely resembling the chicken you buy in a supermarket. YOu get a, frankly, scrawny-looking carcass, with not much white meat and because you have to grow them out to 14-20 wks to get any meaningful amount of meat off them, it will have more texture than that soft squishy supermarket chicken, too. Also you will have spent much more time and much more money on feed, per pound of meat produced, than if you'd grown meat chickens e.g. CornishX.
However, meat from dual-purpose breeds will also have SPLENDID flavor, and many people PREFER the firmer texture, and it will be from happier chickens.
I have speckled sussexes (from a line with large body size) for this purpose; other common choices would include rocks (any color) or wyandottes (any color), but there are lots of possibilities. Make sure you're getting birds from a suitable line - some hatchery stock is very small-bodied and not as useful for the pot.
Good luck, have fun,
Pat