Calories are units of energy. They are a measure of the potential energy, stored in the chemical bonds within the food that we eat. We extract this energy through digestion, and use it to perform various daily functions, such as skiing, brushing up on your archery skills, and even performing a handstand.

There are two types of calories.

  1. Large calories, which are written with a capital C.
  2. Small calories which are written with a small c.

Nutritional calories, or the calories that we see on food packaging, are large calories. The word calories are specifically written with a capital C. One large calorie is equivalent to a thousand small calories or 4,184 Joules. Scientifically speaking one large calorie is equivalent to the amount of energy required to heat one kilogram of water by one degree Celsius. In our diets, we primarily get calories from three macronutrients:

  1. Fats
  2. Carbohydrates
  3. proteins


In terms of energy, fats are the densest macronutrient. They measure in at a whopping 9 Calories per gram.


Though delicious, carbohydrates are less dense than fats measuring in at 4 Calories per gram.


Lastly, we have proteins. Measuring in at 4 Calories per gram, proteins have the same energy as carbohydrates.

Although we may not consume it daily, alcohol is a source of energy as well. Measuring in at 7 Calories per gram, alcohols have more energy than both proteins and carbohydrates. Humans are primarily interested in Calories because we count them for the purpose of changing our weight. In one pound of body mass, there are about 3,500 Calories.

If you consume more Calories than your body utilizes in a day, you’ll gain weight. If you consume fewer calories than your body utilizes in a day, you’ll lose weight. So, how do you determine the number of calories that your body needs on a daily basis? With so many different diets out there, it can seem quite confusing.


To figure out your body’s daily caloric needs, let’s determine your total daily energy expenditure or TDEE. This is the amount of energy or number of calories that your body utilizes in a day, which is based on three components:

  1. The first is your basal metabolic rate.
  2. The second is something called the thermic effect of food.
  3. The third is the number of Calories your body utilizes during physical activity.

The sum of these three components determines your total daily energy expenditure.


Your basal metabolic rate or BMR is a measure of how many calories your body needs on a daily basis just to keep you alive. These are the Calories you would burn if you stayed in bed all day and did nothing.

Even sedentary, your body needs energy to keep your lungs inhaling, heart pumping, and body temperature constant. Each person’s BMR will vary according to many factors. The most recent and accurate formula that is used to estimate BMR is the Mifflin-St Jour Equation.

This equation takes your weight, height, and age into account.

To calculate your BMR,

BMR = (10 x weight) + (6.25 x height) – (5 x age) + S

In the above formula, your weight must be in units of kilograms Your height must be in units of centimeters and your age must be in units of years.

For the parameter S use 5 if you’re a male and -161 if you’re a female.


The thermic effect of food or TEF is based on the fact that it takes energy to digest the food that we eat we eat. We burn approximately 10% of our daily caloric intake by just digesting that food and turning it into usable energy.

For example, if you consume 2500 Calories a day your body will use about 250 of those Calories in the process of digestion.


Thirdly, many of us perform physical activities throughout the day such as running, stretching, and jumping. Each of these activities burns Calories and therefore, these numbers must be added to your total daily energy expenditure.


The amount of energy expended in a day differs for each individual. In general, your basal metabolic rate is the largest component comprising about 50 to 65% of your daily energy requirements. The thermic effect the food is the smallest component comprising 10% of your daily energy requirements. Lastly, depending on how active you are, about 30 to 50% of your daily energy requirement could come from physical activity.


In summary, we need calories to sustain life. Our daily energy needs come from the Calories in the food that we eat. If your body is in energy balance, the majority of Calories that you consume fuel your basal metabolism. Some of those Calories are needed to digest food and the remaining Calories provide us with energy to keep physically active.


Each person’s daily energy requirements will vary. In addition to your age, weight, gender, and height additional factors such as your genetics, amount of gut bacteria, and body composition affect your body’s ability to utilize the energy that we extract from food. With so many contributing factors, there is no one diet that will suit everyone’s needs.