A step further is to cut out fast food, boxed food, or anything pre-made. You should be doing 90% of your shopping in the produce/meat/dairy sections of the grocery store. The vast majority of anything you buy in aisles is either bad for you or incredibly calorie dense.

Unfortunately nutrition doesn't seem to be taught in high school, and cooking at home is an optional course. Learning how to take care of your body and having the tools to be healthy if you choose is beneficial to everyone; much more useful in day to day life than almost anything you learn after grade 8.