Conventional wisdom suggests that if you exercise you will lose weight. This is simply not true. 
There is also a lot of incorrect information surrounding exercise and weight loss.
If you do an hour daily of extreme aerobic exercise and daily consume much more calories than your body burns, you will not lose weight (as you consumed more food than your body burned)
Having a few extra pieces of cream pie or some extra slices of chocolate cake after visiting the gym, is not a good idea. Neither is justifying a binge on some extra burgers and fries because you have done your 30 minutes of cardio.
Overly physically active people do not burn more calories than moderately active people. 
The average calories burned are men: 2600 and women: 1900 irrespective if you do aerobic exercise all day long or are only moderately active.
Yes, sitting on your office chair is not healthy, but doing exercise all day long will not result in you burning more more calories if you are already moderately active.
If you are not moderately active and permanently live on your couch, you may burn around 8% less calories than someone that does aerobic exercise all day long. But if you live on your couch and you are moderately active (walk the dog, etc) in all probability burn the same amount of calories than a person who is overly active and exercises all day long.
So, although exercise is healthy for your body, it is not the answer to weight loss.
Among the benefits of Exercise are healthy heart, better brain function, healthy immune system and generally, just a more healthy body.
Too much exercise reduces the body resources available to fight infection, inflammation and disease.
To lose weight: You need to eat the correct foods and eat less of those correct foods.
Current Biology, Herman Ponzer
PLOS ONE Vol7 No 7 Article:e40503