I am by no means against working out, but forcing this dichotomy may dissuade people from taking a simple an useful step that could even be aggregated: Stretch out your previously brief ice cream consumption while doing your normal schedule AND go for that walk. BAM! You're an even bigger winner.

One first-order approximation is 100 calories per mile for 180-pound person.

Say you walk 2 miles; you've hit about 200 calories. So a wash, and you had to wolf down your food.