The term “empty calories” almost sounds like a conflict in terms—kind of like “cold sweat.” After all, something can’t be empty and full. Or can it? It sure can—if you’re talking about empty calories.

Simply put, empty calories are calories in your foods that are, for the most part, empty of significant nutritional value. And these empty calories can rack up very quickly. Most fats and added sugars are considered empty because they don’t offer your body much, if anything, in the way of vitamins, minerals, phytonutrients or fiber. What they do offer is a fast track to a bigger belly, hips and thighs. So, don’t let the expression fool you—empty calories are anything but.

To make matters even more confusing, foods containing a lot of empty calories are sometimes dubbed “energy dense,” which sounds a lot better than it actually is. But when you’re talking about energy in food, it’s simply a gentler way of saying calories. The calories in the foods you eat are converted into energy that fuels the body.

So, an energy dense food is one that contains a lot of calories (okay, energy) in a relatively small volume. Like the 250 calories of energy you get from a tiny frosted doughnut, or the more than 300 calories you get from a handful of potato chips!

Common Sources of Empty Calories

Sometimes you know when you’re taking in empty calories: sugar is hardly hidden in a carbonated soda or a candy bar. But empty calories aren’t always quite so obvious—like the 5 teaspoons of fat hiding in your blueberry muffin, and the 8 teaspoons of sugar lurking in the fancy coffee drink you use to wash it down.

Sugary drinks are a big contributor to empty calories in the diet. They’re not just in sodas and coffee drinks, but also heavily sweetened teas and fruit drinks like lemonade. Same goes for sugary candy, pancake syrup, honey and preserves. And fatty foods like chips, French fries and salad dressings are mostly empty calories, too. Desserts can deliver a lot of extra energy into your system—most cakes, cookies and pastries pack a one-two punch of sugar and fat.

Swap Empty Calorie Foods for Nutrient Dense Foods

Taking in extra calories that you don’t need is only one problem with empty calorie foods. There’s another equally important issue. When you fill up on fatty, sugary foods, they take up space in your stomach, squeezing out room for all those good-for-you foods that provide the healthy nutrients your body needs.

Here’s the solution in a nutshell: since empty calorie foods have lots of calories and very little nutrition, you want to shift your focus towards foods that are exactly the opposite. You want to eat more foods with an abundance of nutrients with a relatively low calorie cost. Nutrient dense foods like vegetables, fruits and lean proteins offer up plenty of nutrition. They’re filling but they won’t break your calorie bank.

Nutrient dense foods are pretty easy to spot. Since fats are so calorie dense (there are about 40 calories in a teensy pat of butter), swapping high fat items for low fat ones is an easy way to increase your nutrient density and cut out some empty calories. Simple swaps—like replacing whole milk with nonfat, or cooking with ground turkey breast instead of beef—are a great way to start.

Another clue to nutrient dense foods is their water content. Water adds volume but no calories to foods like fruits and vegetables, which makes them relatively low in calories and also filling. They also happen to have an abundance of vitamins, minerals, phytonutrients and fiber. So, you might want to start your meal off with a leafy green salad or a vegetable soup, and begin to fill up on low calorie items. And add vegetables to foods like soups, stews, casseroles and pasta sauces to pump up the volume and the nutrition.

Why Nutrient Density is So Important

I encourage everyone to use their calories wisely, and to spend them on the most nutritious foods they can. This is particularly important for those who have relatively low calorie needs. A woman who maintains her weight on 1400 calories a day will have to choose her foods carefully if she’s going to try to pack in all her nutrient needs without gaining. But even those with high calorie requirements shouldn’t assume they’ve got plenty of calories to spare. Even if you’ve got calories to spare, it’s still wise to eat as many nutrient dense foods as you can.

That said, there’s nothing wrong with a calorie dense treat once in a while. What really matters is the quality of your diet overall. As long as most of the foods you eat are nutrient dense, an occasional high-calorie indulgence shouldn’t be a big deal.