[apelapan]

This seems to be the most common situation, but it is not the only one. Plenty of people have lost significant weight by taking up exercise and not doing any active, concious changes to their diet.

I myself have lost 15kg over the past couple of years, after going from zero high-intensity physical activity on a normal week to a few hours of running and swimming every week.

I'm sure there are some unconscious changes to my eating, in particular afternoon/evening snacking. But that just happened without me trying or planning for it. I still eat at the same lunch restaurants and it is still my wife making me dinner most evenings.