Your thesis can be about ANYTHING that could possibly answer the question asked in the essay, that's if it's a question. If it's a statement or a demand to be answered like "explain how sedentary lifestyles lead to people developing health issues" than the three things that I told you that you needed still apply, at least as far to my knowledge.
Do you know what your being asked/demanded to do in this essay specifically?
Do you know what your being asked/demanded to do in this essay specifically?