In addition, remember the purpose of your writing. If you are going to make any statistical declarations, you must include data from a control group (i.e. people who do not consume soda) to compare data findings from your experimental group (i.e. people
who consume soda.)
Secondly, what is the purpose of your essay? Such as to inform, persuade, entertain, or peer review...
If you are informing people about the risks/rewards of soda, then I agree that your target audience should be the consumer: people with weight/health/disease concerns. You should include research findings that link soda as the cause of their concerns.
If you are writing to persuade, then maybe your target audience should include school health board, department of health officials, and the food and drug administration (FDA).
Your essay doesn't sound like it's purpose is to entertain, or you would not be focusing on the serious topics you mentioned.
Finally, to write a peer review, and to check previously found data, your audience will be other professionals in the field. This is where you must use caution to avoid bias in your research. If you only look at connections that soda has to health, you
might miss other factors that lead to the same results, so you have to look at effects on non-soda users as well.
Good luck, and I hope the website I recommended gives you some direction for your studies.