What should you eat food?Why are they unhealthy food and drink

What does "they"? refer to ?

What should you eat food? = What food should you eat and not eat
Healthy foods, like fruits, vergetables
eat less junk food (snacks)
Why are they unhealthy food and drink = Why are some foods unhealthy
because they contain unhealthy ingredients

你将要吃什么样食物

I understood your question and I'm going to answer it. Why you named some food as unhealty food and unhealthy drink? That because we call them"junk food"
Those food and drinking usually contain a lot of calories but do not contain much nutrition, such as fried chicken, hamburgur, instant noodles(方便h面), or something like that. In drinking, many something like cocacola which contains sugar in it.
So people who eat them often will possibly got some diseases caused by obesity(肥胖), and thus why we called it is not healthy food.
P.S: I wrote by myself, is it satisfying?

Please say clearly?