You could narrow the topic of obesity in certain groups of people even more by adding a sub-topic.
| an age group | Obesity in youth |
| a location | Obesity in the U.S. |
| an additional topic | Obesity prevention |
| a population | Obesity in women |
| a timeframe | Obesity in the last 5 years |
It is helpful to write out your topic as a sentence or a question. Let's say the question that most interests you is: