What are Calories and how do we use them?

A booming Health & Fitness industry means more people are getting fit and taking care of their bodies. With this comes exposure to various training regimes, eating plans and diets (good & bad), many of which are based around calorie intake.

So now more than ever people are talking about, or at least thinking about calories. You cut calories, you count calories and you burn calories, but do you actually know what a calorie is and how it affects your body?

An average man needs around 2,500kcal (10,500kJ) a day. For an average woman, that figure is around 2,000kcal (8,400kJ) a day. These values can vary depending on age and levels of physical activity, among other factors.

What is a Calorie?

In short Calories are a measure of the amount of energy in food. More specifically, a calorie is the amount of energy needed to raise the temperature of 1 litre of water by 1 degree Celsius.

When you eat food, you’re consuming the energy that is stored within the protein, carbohydrate, and fat molecules of that food (macronutrients). The total amount of energy stored in the food you’re eating is represented by the calorie content of the food as indicated on its nutritional label.

How does your body use Calories?

Your body is capable of doing only two things with the calorie energy it absorbs; it must either burn it or store it. This is how the effect of calories on our bodies can be explained according to the first law of thermodynamics.

When we eat food the calories that are in it can never disappear or be destroyed, they can only change form. In their food form calories are stored as chemical energy in the bonds of the food molecules.

When we eat them, calories do not disappear, they’re transformed, or “burned,” into the different types of energy that your body produces and utilises each day. These include heat energy, electrical energy, sound energy, and kinetic (movement) energy, OR, if they aren’t burned, they are stored again as chemical energy.

Therefore, according to the first law of thermodynamics, any calories that you consume and do not burn must be stored in your body. And, unfortunately, the primary storage mechanism for the excess calories you consume is fat, rather than muscle. Damn!

The body uses calories for three distinct activities:

  1. Firstly and most importantly is your basal metabolic rate (BMR), or how many calories your body burns just to keep the basic operations going — heart beating, kidneys functioning, lungs breathing. 60 – 70% of all calories go toward just keeping your body operational, kind of like overhead expenses. To work out your BMR use the calculator provided at the end of this post.
  2. The body also needs calories for physical activity, be it cleaning the house, walking your dog, or more importantly running a marathon.
  3. The third component of calories burned is the thermic effect of food, or how much energy it takes to digest your food and turn it into energy. Your body burns 10% of overall calories consumed to fuel the digestion process.

Calories in food

Foods and drinks are made of mixtures of macronutrients: protein, carbs, and fat. Protein and carbs each contain four calories per gram, while fat contains nine calories per gram. These caloric amounts represent the amount of potential energy these macronutrients provide.

Knowing the calorie content of foods can be a useful tool when it comes to achieving or maintaining a healthy weight. It can help us keep track of the amount of energy we’re eating and drinking, and ensure we’re not consuming too much.

These days the calorie content of most foods is stated on the packaging in the nutrition label, which you will often find on the back or side of the packaging. This information will appear under the “Energy” heading.

The calorie content is often given in kcals, which is short for “kilocalories”, and also in kJ, which is short for “kilojoules”.

A “kilocalorie” is another word for what is commonly called a “calorie”, so 1,000 calories will be written as 1,000kcals. Kilojoules are the metric measurement of calories. To find the energy content in kilojoules, multiply the calorie figure by 4.2 (or vice versa – to go from kilojoules to calories divide the kiljoules by 4.2).

The label will usually tell you how many calories are contained in 100 grams or 100 millilitres of the food or drink, so you can compare the calorie content of different products.

Calories In vs Calories Out

The fundamental law that governs whether you gain or lose weight is the first law of thermodynamics, which states that energy cannot be created or destroyed, it can only be transformed from one type to another.

Although thermodynamics itself isn’t generally a simple subject, calories are explained quite easily according to its principles. Ultimately, your body weight is dependent on the difference between the amounts of calories that you consume versus the amount of calories that you burn. This is known as your caloric balance.

Everything you eat and drink contains calories, therefor they’re nicknamed calories in. Everything you do burns calories. From intense exercise like running and weight training, to everyday tasks like standing, tying your shoes and most importantly, staying alive. Because these are the calories your body is using up, they’re nicknamed calories out.

Weight control is all about the battle between calories in and calories out. If they’re both equal to each other, your weight will stay the same. But, if one is higher than the other, your weight will change.

Put simply, if you consume more calories than you burn, you gain weight. If you burn more calories than you consume, you lose weight. And, if you both burn and consume the same amount of calories, your weight stays the same.

Calories & Exercise

The amount of calories people use by doing a certain physical activity varies, depending on a range of factors, including sex, size, age and the individuals metabolism.

The more vigorously you do an activity, the more calories you will use. For example, fast walking will use more calories than walking at a moderate pace, and running will burn more again.

If you really want to burn calories fast during exercise research shows that HIIT training (high intensity interval training) burns more calories than longer, lower intensity aerobic workouts. Find out more about HIIT here.

I’ll provide a more comprehensive guide to calorie burn rates during exercise in future posts, but for your convenience I’ve included a calories burned calculator below.

I hope this article has been useful in explaining the basics about the sometimes dreaded Calorie and how your body uses them to fuel your every move. Keep an eye out for future posts that will go further in explaining how your body works and how to maintain a truly healthy lifestyle.

Leave a Reply

Your email address will not be published. Required fields are marked *