I need to write an introduction of an essay about food
What have you said in your essay? We can't introduce something without knowing about it.
I did not write anything yet, I am stuck at the opening paragraph.
what about food???? the industry?, the variety?,healthy vs unhealthy?
just food in general.
You can not write an opening paragraph without knowing what's in the paper.
Brainstorm what you want to say about food. Decide on a thesis statement. Outline your three arguments for supporting your thesis.