There is no secret to weight loss. Diet plus exercise equals results.
What is better for weight loss, diet or exercise?
While both are very important in overall weight loss and health, diet can by far have the most impact on your weight loss goals.
The reason for this is clear when we look at the most basic rule for weight loss:
To lose weight you must use more calories (energy) than you consume.
For the biggest weight loss possible, you either need to burn more calories each day, or consume less calories. It is much easier to consume less calories than it is to burn more calories through exercise.
The best proof of this is an example. A 65g Mars Bar contains 1135 kJ of energy (or 270 Calories). It would take an average person approximately an hour of walking at a moderate pace to burn the same amount of energy.
I don't know about you, but I'd rather my 1 hour walk each day burn fat off my body instead of burning off the single Mars Bar I just ate... :)