The concept goes something like this: some veggies are so low in calories that they require more energy to digest than they contain. The result? Eating celery, cucumbers or iceberg lettuce can give you a “negative calorie balance.” Sounds great in theory, but “the calories you need for digestion won’t ever exceed the number of calories any type of food contains,” says Los Angeles-based nutritionist LeeAnn Smith Weintraub, RD. However, these non-starchy, low-calorie veggies can still help you lose weight since their fiber and water content will keep you feeling full for longer. So go ahead and pile them on generously when you hit the salad bar for lunch.

You’ve heard “a calorie is a calorie,” meaning your body processes them all the same way regardless of where they come from. But not so fast: 100 calories of chocolate cake are not the same as 100 calories of carrots. As it turns out, your body burns nearly 50% more calories after eating a meal packed with whole foods versus an equivalent meal made of processed fare, according to a 2010 study published in the health journal Food & Nutrition Research. During manufacturing, processed foods are broken down and stripped of many nutrients, making it easier for the body to digest them. On the other hand, whole foods, such as multigrain bread, apples or zucchini, contain good-for-you nutrients like fiber that the body has to work overtime to break down, temporarily boosting metabolism. Plus, “eating smarter calories via foods packed with filling fiber or satisfying protein, like a chicken breast instead of potato chips, will help you naturally eat less over time,” explains Weintraub.