An uncommon view that, no doubt, some readers may find objectionable: exercise may modulate mood more than it affects long-term weight loss. 

Here is one quote:

One reason diet may play such a strong role in weight loss is that exercise burns off far fewer calories than most people think, said Philip Stanforth, a professor of exercise science at the University of Texas and the executive director of the Fitness Institute of Texas.

That is from Erin Brodwin via Business Insider, Link here