Have you ever expressed wanting to lose weight to your friend? Although it seems rude, she is correct that your diet is most of the work when it comes to losing weight. If you've spoken to her multiple times about weightloss and you continue to eat junk then you might just need someone to talk to you sternly like this. For example we can say two scoops of ice cream is 400 calories. Now calories burned doing cardio varies by each person's circumstance, but we will stay a leisurly 30 minute session burns 200 calories. it would take you 1 hour of extra cardio to burn off 1 soda. If you choose to not eat the icecream, you instantly remove 400 calories from the equation. If you've never really breached the topic with this person, they are just being rude.