Smart shoppers usually look for value – whether they’re buying a car or a computer, they want to get the best bang for their buck. The same rule should apply to food, too. When the currency is calories, it’s smart to spend them as wisely as you can.

Clearly stated, the concept of nutrient density is pretty simple. It refers to getting the most “nutritional value” for your “calorie intake.” Foods high in protein are going to give you an abundance of nutrients in exchange for relatively few calories.

A healthy diet does more than just keep calories in check. If body weight were the only thing that mattered, you could keep your weight steady on French fries and chocolate cake, as long as you didn’t eat more calories than you burned off. But, of course, we need a complex array of proteins, carbohydrates, fats, vitamins, minerals, and phytonutrients from plants to keep ourselves in peak condition.

Whether you’ve heard the term or not, if you try to eat reasonably well, you’re probably already eating a pretty nutrient-dense diet. Most people know what foods make up a healthy eating plan: fruits, vegetables, lean proteins, low fat dairy products. and whole grains – and these are some of the foods with high nutritional value.

Part of the high nutrient-to-calorie ratio in these foods is their low fat content, which means they pack a lot of calories per bite. And, because water has no calories, watery foods like fruits and vegetables have the fewest calories per bite – but they’re loaded with nutrition, making them some of the best foods you can eat.

A single orange supplies a whole day’s vitamin C and a host of other nutrients, too – in just 70 calories. If you tried to meet your vitamin C needs from French fries, you’d need to eat about 800 calories’ worth. That’s because fats seriously dilute the ratio of nutrients to calories. Sugars do, too. Fats and added sugars are the flip side of nutrient density. They pack an abundance of calories but not much of anything else. This is why we call them “calorie-dense.”

Have three ounces of grilled fish for dinner, and you’ll get about 25 grams of protein, along with minerals like iron, zinc, and magnesium, all for about 120 calories – a true calorie bargain. Sure, you can get 25 grams of protein from a burger, but it will also cost you an extra 400 calories or so.

Everyone should aim for a nutrient-dense diet, but it’s particularly important for those whose calorie requirements aren’t that high to start with. A middle-aged woman who only needs 1400 calories to maintain her weight will be hard-pressed to pack all her nutrient needs in a small calorie package if she doesn’t choose carefully; she simply can’t afford a calorie-dense meal.

Don’t lose the forest for the trees, though. Of course it’s wise to eat as many nutrient-dense foods as you can, but there’s nothing wrong with a high-calorie treat once in a while. Focus on the quality of your diet as a whole. As long as your overall diet has a high nutritional value, that’s still smart spending.