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 burnFat and energy balance. Pagliassotti, MJ, Gayles EC, Hill JO. Department of Pediatrics, University of Colorado Health Sciences Center, Denver 80262, USA. Annals of the New York Academy of Science, 1997 Sep 20;827:431-48.Is a calorie a calorie? Buchholz, AC, Schoeller, DA. Department of Nutritional Sciences, University of Wisconsin-Madison, 1415 Linden Drive, Madison, WI 53706, USA. The American Journal of Clinical Nutrition, 2004 May;79(5):899S-906S.Are all calories created equal? Emerging issues in weight management. Hollis, JH, Mattes, RD. Purdue University, Department of Foods and Nutrition, 700 W. State Street, W. Lafayette, IN. Current Diabetes Reports, 2005 Oct;5(5):374. 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 movingMeasuring the thermic effect of food. Reed, GW, Hill, JO. Clinical Nutrition Research Unit, Vanderbilt University, Nashville, TN. The American Journal of Clinical Nutrition, 1996 Feb;63(2):164-9.. 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 differentEnergy and macronutrient metabolism. Swinburn, BA, Ravussin, E. Department of Community Health, University of Auckland, New Zealand. Baillière’s clinical endocrinology and metabolism, 1994 Jul;8(3):527-48.. 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)What are the health effects of fat? Wahrburg, U. Fachhochschule Munster, Fachbereich Oecotrophologie, Munster Germany. European Journal of Nutrition, 2004 Mar; 43 Suppl 1:I/6-11Saturated fatty acids: simple molecular structures with complex cellular functions. Rioux, V., Legrand, P. Biochemistry and HUman Nutrition Laboratory, Agrocampus Rennes, Rennes, France. Current Opinion in Clinical Nutriton and Metabolic Care, 2007 Nov; 10(6):752-8.The negative effects of hydrogenated trans fats and what to do about them. Kummerow, F.A. Department of Bioscience, University of Illinois, Urbana. Atherosclerosis, 2009 Aug;205(2): 458-65..
Some studies suggest that certain foods actually, over time, take more energy for the body to break down than is listed on nutrition labelsWeight-reducing diets: are there any differences? Foreyt, JP, Salas-Salvado, J, Caballero, B, et al. Department of Medicine, Baylor College of Medicine, Houston, Texas 77030, USA. Nutrition Review, 2009 May;67 Suppl 1:S99-101.. 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 uptickMeasuring the thermic effect of food. Reed, GW, Hill, JO. Clinical Nutrition Research Unit, Vanderbilt University, Nashville, TN. The American Journal of Clinical Nutrition, 1996 Feb;63(2):164-9..
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 gramWeight-reducing diets: are there any differences? Foreyt, JP, Salas-Salvado, J, Caballero, B, et al. Department of Medicine, Baylor College of Medicine, Houston, Texas 77030, USA. Nutrition Review, 2009 May;67 Suppl 1:S99-101.. 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.
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 excessMeal size and frequency: effect on the thermic effect of food. Tai, MM, Castillo, P, Pi-Sunyer, FX. Obesity Research Center, St. Luke’s-Roosevelt Hospital Center, Columbia University, New York, NY. American Journal of Clinical Nutrition, 1991 Nov;54(5):783-7.. 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).