It's not always the calorie count but the type of food?
We need to eat for energy, the fast food doesn't supply the body with energy it actually makes the body work harder thereby leaving you tired etc.
The key here is to eat for energy and fat is the way to do it but it has to be a plant based fat in moderation, like 1/4 cup of nuts, they keep you full longer, so you eat less, so you'll lose weight but still have the energy to do what you need to.
As far as salad goes, if you add things like beans, peas, lentils or nuts to your salad then's when you're adding energy but just a plain old salad offers vitamins and minerals not any energy.
Look at it like this 2/3 cup of shelled pistachios has 330 Calories, Burger and Fries 800-900 Calories. Eat the nuts as you get more energy, fiber, vitamins & minerals and the body doesn't have to work very hard to break them down.
Hope that makes sense!