As a matter of fact, I'd argue that diet is the single most important part of losing weight. Whenever I need to drop a few, I tweak my diet. I have always been an active person. I can easily gain 5 pounds in a weekend by eating. And I can easily drop 5 - 10 pounds by cutting calories. These land whales will argue until they pass out about how diets don't work, just so they can continue to clutch onto their bags of cheetos.