Recently, a woman came up to me to say how frustrated she was that she was not losing weight, despite eating all the "right" foods—whole grains, fat-free dairy, and of course lots of fruits and vegetables. The mistake she was making is a common one: mixing up the idea of the healthiness of food with its energy (calorie) content.
People have, of course, lost weight on diets rich in foods generally thought of as healthy, but they've also lost weight on both high-fat and low-fat diets, and even on diets consisting only of food purchased at McDonald's or composed largely of Twinkies. Fad diets that promote "magical" foods gain their power from restricting calories, not from the special qualities of grapefruit or apple cider vinegar.
BOTTOM LINE: The healthiness of a diet is separate from its calorie content. This isn't to say that you shouldn't eat a healthy diet. But you can't ignore the calories if weight loss is your goal.