Student or Learner
I wonder if there is any difference between " a healthy foods" and "a healthy diet".
There is a great deal of difference.
Today's wisdom dictates that healthy foods are those that are low in fats, sugars, cholesterol and sodium (among other things). Helathy foods are high in fiber, vitamins, calcium, iron and protein.
A healthy diet is one that is - above all - a balanced diet. We are hardwired to crave sweets and fats for their caloric value. But it is important to remember that for the optimal functioning of the "machine" that is our body, we need to balance the types of foods we eat so that we do not favor high caloric value over lean protein and (non-processed) cereals. A healthy diet is one that favors healthy foods but allows for human nature and it's need for an occasional chocolate bar.
You have received an excellent reply, but please note that "a healthy foods" (as you put in your original question) is not correct English.