When your topic is too broad, it can be difficult to research and even more difficult to write about! Therefore, be sure you have a focused topic. Here are some tips to help you narrow your topic so that it's manageable and focused.
The 5 W's and 1 H
Take your larger topic, and consider the 5 W's (Who, What, Where, When, Why) and 1 H (How). There are no right or wrong answers for this exercise! So just consider what interests you and what fulfills your assignment. For example: obesity as a topic is too broad, but if we use the 5W's and 1 H, we can narrow the topic down: