By that definition Burger King is food, you can survive on it and gain enough nutritional value to allow you to grow.
Technically, dirt contains some nutritional value. So yeah, you are correct that fast food does contain some nutrition. Eating a diet of strictly potatoes will, technically, allow you to "grow" but like industrial fast food, will come with adverse health consequences. So the question isn't if it technically has some amount of nutritional value but whether it's actually good for you. Does the "food" allow you to maintain life and grow to a degree consistent with the average seems to me to be a reasonable definition.
A diet with a lot of fast food is nutritionally poor and full of many things such as sugar, salt, and saturated fats that cause long-term adverse health consequences. It's been linked to everything from a lower capacity for memory and learning to diabetes, heart disease and of course obesity.
There is simply no way that you can say that fast food is "good" for you or that it should be eaten routinely. Making the clear distinction that fast "food" is not food to the same degree as a healthful diet is one of the best things you can do for community health.