What Is a Calorie?

“How many calories are in that?” is a common concern when looking at food labels.  What is a calorie though?  Why do we get so fixated with calorie amounts?  The term is calorie simply a way to measure energy.

When we want to know how many calories are in a food, we basically want to know how much energy a food can provide.

What is a Calorie?

A calorie is a way to measure the energy coming from food.  The body uses energy from food to provide energy to all the cells of the body.

The term calorie dates back to 1863 where it was used to measure how much energy was needed to raise one kilogram of water one degree Celsius.

The calorie on nutrition fact labels we see is actually considered a kilocalorie.  One kilocalorie is equal to 1,000 small calories.

However, the kilo is usually dropped and the term “calorie” or “Calorie” is usually used in place of kilocalorie.

Adjusting our calorie intake is a main way we can affect our weight.  Cutting out excess calories is a main component for most diets advocating weight loss.

It was thought if you just lower your calorie intake, your body will have less energy in and will burn extra fat for fuel.

However, as more and more people started short term dieting, weight loss was not consistent.

What is now also known is quantity of calories is not the only thing affecting energy balance.  The quality of those calories is also an important part of the equation.

How the body uses calories from food

The macronutrients that provide calories are protein, fat and carbohydrates.

On average, carbohydrates and protein provide 4 calories per gram, alcohol provides about 7 calories and fat provides about 9 calories per gram.

When we eat food, there is a mix of carbohydrates, fat and protein that provide energy to the body.

The first step that needs to happen when we eat or drink food is to break down the food into single molecules.

This is done during the digestive process, and single units of carbohydrate, proteins and fats get absorbed into the blood stream across the small intestine wall.

When these units are in the blood stream, the body can direct them to various cells that need energy or can be stored.

As carbohydrate levels (as glucose) start to rise in the blood stream, insulin gets released.  Insulin acts as a gate keeper to let glucose into body cells and out of the blood stream.

Every cell needs energy from food to function.  Every cell uses energy for various processes including metabolism, signaling pathways, to make new cells and contract muscles.

We can store extra energy in the form of glycogen and fat stores.  When energy intake is not adequate, the body can break down glycogen to provide carbohydrate and break down fat stores to provide energy.

Adjusting calorie amounts for weight regulation

It has long been suggested to lose weight you need to lower your calorie intake.  The less fuel you give your body, the more reliance on fat stores as a fuel source.

While this thinking is partially true, what also needs to be accounted for is the body’s complex system.

As calorie intake drops, metabolic rate also can slow down. Hormones that regulate metabolism can also have an impact on weight regulation.

For example, if calorie intake goes very low, cortisol and ghrelin, which increases appetite, can be increased.

How much energy your body needs can depend on many things: age, sex, body size, activity level, genetic factors and hormone levels.

While we can give an estimated calorie range for weight loss, maintenance and weight gain, there are other factors that influence weight in addition to how many calories you eat.

Estimated calorie needs can be gathered from plugging in your age, weight, height and gender into equations like the Harris Benedict Equation.

Plugging in these numbers can give an estimate of your body’s calorie needs.  However, there can be individual variance for the calorie number given in these equations.

The thought is matching the calorie intake from food to the number in the equation should keep you in weight balance.

Increasing or decreasing your calorie intake should increase or decrease body weight, respectively.

All calories are not created equal

Do you just need to stay under a certain calorie limit for weight loss, or is there more that should be looked at?  Is a calorie a calorie no matter where it comes from?  Does your body handle a calorie from spinach the same as a calorie from candy?

It turns out the body handles calories differently.  Quality of calories should also be factored in for health and weight besides just quantity.

A 2010 study (1) compared the differences in postprandial thermogenic responses after a meal with whole food compared to a meal that was from processed food.

Meals were comparable for total calories, carbohydrate, protein and fat content.  Researchers found the processed food meal had 50% lower postprandial energy expenditure than the whole food meal.

What does this mean?  The body uses more energy to break down whole foods compared to processed foods.

Research (2) has also shown macronutrients have varying levels of energy expenditure to break down.

For example, protein has higher energy expenditure to break down compared to carbohydrates.

This may be one reason why higher protein diets can be advantageous for short term weight loss.

The body handles a calorie coming from a high protein food different than from a high carbohydrate food.

Conclusion: What is a calorie?

A calorie is a way to measure the energy coming from food.  The body uses energy from food to provide energy to all the cells of the body.

Extra energy from carbohydrates and fat can be stored in case the body needs to use it as fuel at a later time.

We can look at the calorie amounts on food labels to gauge how much energy we get from foods.  However, there is more than just the total calorie amount we should be concerned with.

How the energy is packaged can make a difference on how the body handles the energy.  Other nutrients like vitamins, minerals, antioxidants and fiber should come with the energy we get from food.

This is called nutrient density.  Consuming high nutrient dense foods is recommended.