Eating snacks with the right ratio of nutrients, with the right calories, will help keep you body energized and help you lose weight. Protein (plus exercise) fuels the growth of lean muscle mass, which boosts metabolic rate and increases calorie burn. Fiber, meanwhile, helps improve digestion and keeps you from binging on fats and sugars. So while there's no food that will literally "burn fat" while you eat it, smart choices with these ingredients will help your body operate at maximum efficiency. Bowerman suggests snacks under 200 calories, with 10 grams of protein and close to 5 grams of fiber. Here are 20 of our favorite fat-burning snacks.

"Almost any fruit is going to make a great snack, but you usually want to pair it with a bit of protein to make it more satisfying," says Bowerman; "unlike carbohydrates, which get used up relatively quickly, protein will help sustain your energy and hunger levels for a couple of hours."

Our pick for a protein-fruit pairing: one large apple and one cup of skim milk. This duo will give you 10 grams of protein and 5 grams of fiber for just over 200 calories. 

 Here's another fruit and diary combo, this one for when you're craving something rich, creamy, and a bit savory. Remove the pit from one half of an avocado and fill the space with 2 ounces of 1% cottage cheese. For 200 calories, you'll get 9 grams of protein and 7 grams of fiber—and no dirty dishes!

 How to Prepare an Avocado: http://www.health.com/health/video/0,,20786793,00.html

If you don't want to incorporate dairy into every snack, a can of tuna (packaged in water) is another great source of lean protein plus healthy Omega-3s. For about 200 calories, you can enjoy 3 ounces of light tuna and 6 whole-wheat crackers—complete with 3 grams of fiber and 20 grams of protein. 

Lentils are a good source of iron, a metabolism-boosting nutrient that 20% of us don't get enough of. This savory recipe makes four 180-calorie servings, with 10 grams each of protein and fiber.

You may not think of shellfish as a grab-and-go snack food, but you can put this tasty treat together in a flash if you keep pre-cooked shrimp on hand. With Greek yogurt and avocado, it's a protein powerhouse with 9 grams per serving (and 4 g fiber), for only 129 calories.