Great question! Here's the deal...
First, a little "Calories 101." Think of calories as energy: the energy your food delivers to your body, and the energy your body burns through physical activity. When you burn the same amount of energy as you consume, you maintain your weight. If you consume more energy than you burn, you're going to gain weight. And if you consume less energy than you burn, you're going to lose weight.
So, I hate to take sides, but… I'm on your side. Yes, eating healthy foods is a GREAT idea. But you need to pay attention to your overall calorie intake and output if you want to lose weight. In order to lose a pound, the general guideline is that you need to take in about 3,500 calories fewer than you burn. In other words, if you're currently maintaining your weight, you'd want to cut about 500 calories per day to lose a pound per week. (Everyone loses weight at a different pace, but that's the basic principle.)
Choosing healthy foods without paying attention to calorie intake won't necessarily result in weight loss. For example, if you eat 4,000 calories' worth of grilled chicken and brown rice each day, you’re probably still going to gain weight. If you eat only 1,200 calories' worth of junk food, you’re likely to lose weight. (But you’ll probably develop some health problems, so I certainly don't recommend it!)
Healthy foods can be high in calories. Take this meal, for example: a salmon salad with almonds, dried cranberries, olive oil, and vinegar; plus a side of brown rice. It's certainly healthy. But even with reasonable portions, that meal can easily total over 900 calories. This is why it's so important to pay attention to calories. They add up.
That said, calories aren't the only thing that matters when it comes to healthy weight loss. Filling your diet with nutritious foods is a great way to support your weight loss. Fruits, veggies, reduced-fat dairy, lean poultry... Healthy foods like these are full of naturally occurring fiber and protein, both of which are very satisfying. (Bonus: Our bodies burn more calories digesting protein than other nutrients, and calories from insoluble fiber aren't digested at all!) And satisfaction is crucial when it comes to sticking to a weight-loss plan. But the key word there is plan -- you can't just eat an unlimited amount of these foods and expect to lose weight. Additionally, it's important to get the right amounts of healthy fats and total carbs. Need a little assistance choosing balanced meals that give you the most bang for your calorie buck? Check out The Hungry Girl Diet and The Hungry Girl Diet Cookbook.
Bottom line: Calories count, but healthy food is the best way to spend 'em! Keep a food journal, jotting down your daily food choices and their calorie counts. And if you overdo it, just get in a little extra exercise! Burn, baby, burn...