Why a Calorie Is Not a Calorie

While it’s important to watch the number of calories you consume, it’s also important to scrutinize the types of nutrients in your diet.

Q: I’ve heard that “a calorie is a calorie.” Is this true?


Not exactly. In a general sense, it’s true that first law of thermodynamics dictates that energy is conserved whether you gain, lose, or maintain your weight. Simply stated, if you consume more calories than you expend, you’ll gain weight. It doesn’t matter whether the calories come from protein, carbohydrate, or fat: Eat too much and you’re sure to pack on the pounds.

That said, some nutrients do have the potential to make you fatter than others. Saturated fat, for example, is easily converted into stored body fat. This has been demonstrated in numerous research studies: Given the same caloric intake, eating saturated fat results in a greater deposition of fat into adipocytes than either protein or carbs.

On the other hand, unsaturated fats, especially the omega-3 variety (abundant in cold water fish and flax oil) have thermogenic properties. They work their “magic” by upregulating various fat-burning enzymes and downregulating various fat-storage enzymes, thereby accelerating the rate at which your body can burn fat.

Moreover, there is also a difference between dietary carbohydrates; specifically, refined and unrefined carbs. Due to their effect on insulin levels, refined carbs tend to be lipogenic (i.e., fat promoting). You see, insulin is a storage hormone that turns on various fat-storage mechanisms and blocks certain enzymes that are responsible for lipolysis (i.e., fat breakdown). When insulin levels are high, excess nutrients are more readily shuttled into adipose cells, resulting in a corresponding increase in body fat.

Furthermore, the rush of insulin clears sugars from your circulatory system in such an expeditious fashion that it creates a rebound effect, producing a sudden and dramatic drop in blood sugar levels. A hypoglycemic state is induced, causing severe hunger pangs and food cravings. This creates a vicious cycle that encourages binge eating. As a result, more calories are consumed (especially in the form of sugar-laden foods) and fat storage is heightened even further.

Alternatively, unrefined, nutrient-dense carbs are processed slowly. They enter the bloodstream in a time-released fashion, keeping blood sugar levels in check. As a result, insulin is stabilized, reducing the potential for unwanted fat accumulation.

Finally, of all the macronutrients, protein is least likely to cause fat storage. One of the biggest reasons is that a large percentage of calories from protein are burned off in the digestion process – a phenomenon called the thermic effect of food. Of all the macronutrients, protein has the highest thermic effect, burning off approximately 25 percent of the calories consumed. In comparison, less than 10 percent of the calories from carbs are burned off in digestion; dietary fat has virtually no thermic effect whatsoever.

What’s more, protein tends to curb appetite. This is largely a hormonal function. When protein is consumed, a hormone called cholecystokinin (CCK) is secreted. CCK acts on the body’s hunger mechanisms, quelling the urge to eat. Given the law of thermodynamics, these appetite-suppressing effects will, in and of themselves, help promote weight loss.

And protein also has an indirect effect on regulating metabolic rate during times of caloric restriction. When you diet, glucose (sugar) becomes in short supply. This has a negative impact on the brain and central nervous system, which rely on glucose as their main source of energy. Sensing a threat to its survival, the body’s internal feedback system begins to break down protein stores into glucose (through a process called gluconeogenesis). Since skeletal muscle is not necessary for sustenance (as opposed to the internal organs and other protein-based tissues), it’s the first thing to be cannibalized for glucose. Why is this important? Well, muscle is metabolically active. For each pound of muscle, your body burns about 50 calories a day at rest. Accordingly, when muscle tissue is lost, metabolism slows by a similar amount.

So, the bottom line is this: While it’s important to watch the number of calories you consume, it’s also important to scrutinize the types of nutrients in your diet. By taking both these factors into account, you’ll be well on your way to achieving your ideal body!

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