[derbOac]

Meta analyses of randomized controlled trials show diet and exercise both are related to weight loss but diet has a much bigger impact.

You have to take this with a grain of salt though. My experience clinically (working in obesity clinics) is some people need exercise much more than dietary changes at least at first. But the average person wanting to lose weight will see bigger gains from dietary changes.

The type of dietary change that works best seems to depend on the person.