Calories are often thought of as public enemy number one (particularly those watching their waistlines). Yes, it’s true that weight control is primarily a function of the number of calories we take in versus the number of calories we burn   . But all those suggestions to eat a balanced diet exist for a reason, because the source of calories matter just as much as the amount. With the right timing and good choices, calories can be more friend than foe, providing all the energy the body needs to not just survive, but thrive.
The Calorie Count — The Need to Know
In simplest terms, a calorie is a unit of energy. Specifically, it’s the amount of energy needed to heat one gram of water by one degree Celsius. The number of calories listed on nutrition labels reflects the amount of potential energy a food contains that can be used by the body. After eating, the body uses the energy to keep our hearts beating, lungs breathing, and muscles moving . When there’s excess energy, it’s stored as body fat. In terms of energy content, all calories really are equal, whether they come from fat, carbs, or protein. One gram of protein, for example, contains four calories. Carbs have the same amount, while fat packs a whopping nine calories per gram. (Alcohol has seven, but isn’t considered a true “macronutrient” since it’s not necessary for survival.) These numbers hold true no matter what kind of food the calories come from. In other words, one gram of sugar from a cookie has just as many calories as one gram of sugar from a carrot. Unsaturated fat from an almond delivers the same calories as an equal amount of saturated fat from butter. But it’s not that simple.
It’s how the body uses calories from these sources that makes them different . Protein rebuilds damaged tissue and creates certain hormones and enzymes. Fat coats our organs in protective cushioning and is necessary to absorb fat-soluble vitamins A, D, E, and K. While unsaturated fats have been shown to improve good cholesterol levels, some research suggests that saturated and trans fats can cause some pretty big issues, including increased cholesterol levels and higher chance of heart disease (though the results are conflicting)   .
Some studies suggest that certain foods actually, over time, take more energy for the body to break down than is listed on nutrition labels . The energy expended by the body purely for the purpose of digesting food is called thermogenesis, or the thermic effect of food. This means bodies burn calories solely to break down food in the stomach and absorb and transport its nutrients. Consequently, every meal causes a small metabolism uptick .
Most research shows that protein has the greatest thermic effect, meaning it takes the most energy to metabolize and store — possibly more than its four calories per gram . Ingesting the muscle-building stuff may increase metabolism by as much as 30 percent from its normal resting rate, compared to fat and carbs’ five percent calorie-burning boost. Protein has also been shown to induce a fuller feeling than it’s equally calorie-dense partners, carbohydrates.
Protein’s ability to both burn calories and keep eaters satisfied has earned it a high status in weight-loss diets, even over low-fat eating plans. On high-protein, low-carb plans, dieters can trade out carbs for an equal amount in protein so the same amount of calories goes in, but the body spends more to digest them. And because protein produces that fuller feeling, dieters may end up eating less overall.
Perfect Protein? — Your Action Plan
Before swapping out every meal for a protein shake, keep in mind that the type of food that a calorie comes from dictates how its energy is used. Carbohydrates don’t provide the same satiated feeling as protein, but they are the body’s main source of fuel that drive organ function and physical activity. And unlike that tempting sugary cookie, carbs from fruits, veggies, and whole grains deliver gut- and heart-healthy fiber (which can help keep BMI low) and extra vitamins and minerals  .
When calories are consumed also plays a role in how food is digested and used. The body is more likely to burn calories immediately — rather than store them as fat — when it’s depleted of energy (like in the morning after a full night’s sleep, or after a tough workout). In these instances, calories are used to store glycogen or repair tissue, not kept on reserve as fat cells. This is why some diets rely on eating multiple small meals throughout the day instead of the traditional three squares: By evenly spacing out meals, the calories meet the body’s immediate needs for energy without excess . On the flipside, restricting calories too much not only means shrinking silhouettes, but shrinking energy and, possibly, shrinking muscle.
So at the end of the day, all calories are equal in terms of the energy they deliver, but differ greatly in the work they perform in the body. The right amount of calories from protein, carbs, and fat ensure the body functions properly. Timing snacks and meals properly can also help make the most use of every calorie (and reduce the body's need to store any as fat).
How do you monitor your calorie intake and the sources they come from? Join the conversation in the comments below!