Generally, the word, fast foods, are  is used for calling the foods such as hamburgers, hot-dogs or sandwiches, etc. These foods are delicious and very convenient because we can have them within a short time. So, many office-men enjoy them when they have no time to wait for a long time in classical restaurants.

However, many professionalists are criticizing the negative effect of the fast foods on our health. As the people consider the quality of their lives, the popularity of the fast foods are is decreasing. Especially parents keep their kids from fast foods.

As a result, sales of the fast food companies (pl) such as McDonald's or Burger-King are decreasing rapidly, and well-being foods are hitting. (becoming more popular?)

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1) Fast food is uncountable. I think the textbook may have made this mistake, so I can understand why you wrote it as fast foods.

2) "well-being foods are hitting"--I think the word hitting here isn't applicable. I think you want "becoming popular" or "being consumed more"

Good job! You always have good ideas laid out nicely. Your structure was especially good in this assignment.