What is a Calorie?

A Calorie is a unit of energy. The word was first used back in the early 1800’s by French scientists to describe the amount of energy needed to heat 1litre of water by 1⁰C.

This is still the definition of the word today in reference to food.

Confusingly, in the mid-1800s other French scientists decided that a calorie would describe the amount of energy needed to heat 1 ml of water by 1⁰C . This is obviously 1000 times smaller than the first definition of the word.

To ensure people understood what was being discussed, it was decided that the Calorie (with a capital ‘C’) would be used to describe the energy needed to heat 1 litre of water, alongside the calorie (with a small ‘c’) which was for a millilitre of water. It was also decided that instead of using ‘Calorie’ scientists could use the word ‘kilocalorie’.

So when we talk about Calories in food, it’s calories with a capital C. It’s also why you might see ‘kcal’ on food packaging. For food purposes, it’s the same thing.

While the word is no longer really used in science, it’s still used to describe the energy in food.

Why?

In 1887 an American scientist named Wilbur Atwater wrote an article about the amount of energy provided by different foodstuffs. He measured the amount of heat given of when various foodstuffs were burned to estimate the amount of energy in that food. He wrote about the different amounts of energy provided by fats, carbohydrates and protein, and used ‘Calories’ as the unit of energy to describe this.

Scientists at the time were looking into the subject as it was a way of ensuring that people carrying out manual labour received sufficient food so that they could work (or a way to decrease the amount they were receiving if you want to be cynical…). If you could say that a certain type of food provided a certain amount of energy, you could compare that with the amount of energy expended doing a job and make sure they were the same. So if I’m a machinist in a factory and I use 1500 Calories of energy a day doing that job, then I need to make sure I eat 1500 Calories of energy per day so I can work to my full potential. Make sense?

So why do we still use the term now?

Because the word is in the public consciousness. People are familiar with it, and recognise the term in relation to food. The amount of energy a foodstuff provides is a quantifiable marker that means you can compare one food to another – rightly or wrongly.

It’s also a pretty neat and rounded descriptor. As in, dietary advice states that humans should eat around 2000-2500 Calories per day. It’s obviously very individualised, but that’s a rough estimate.

Compare that to if we used small ‘c’ calories – you’d be eating 2-2.5 million calories per day. Sounds like an awful lot. Or alternatively using ‘joules’ (which is now the common scientific term for energy), which would be 8.368 million – 10.465 million joules (1 Calorie is 4186 joules). You can see how that could get a bit unwieldy and hard to follow.

How many Calories do I need to eat?

This is wholly dependent on you. Your lifestyle, how active you are, your body type – everyone has a unique Calorie requirement. Plus some days you will need to eat more than other days, it’s not a blanket requirement.

The first thing to understand is that your body uses energy even while it is at rest. So if you’re lying on the sofa watching TV, or sound asleep in the middle of the night, your body is still using energy. Your heart uses Calories to beat, to pump blood around your body. Your brain uses Calories to send electrical signals to the nerves. Your lungs use Calories to breath. To this end, even if you lead a completely sedentary life, your body still requires a Calorie intake to keep you alive. This is called your Basal Metabolic Rate (BMR). This is the amount of Calories your body needs to simply exist. While this figure is also unique to you, there are calculators that can be used to give an estimate of your requirement – you can find these online, just search “BMR calculator”.

To then figure out how may Calories you need to consume, you need to take your activity levels into consideration, and your body composition. Again, BMR calculators can be found online to help you with this. They’ll reference ‘Total Daily Energy Expenditure (TDEE)’. The more you move your body the more energy (Calories) it needs to fuel that movement. The way your body is made up is also an influence. People with higher muscle mass need more Calories because of the way Calories are used by the body. So if you have two people who weigh exactly the same, but one has a higher percentage of their body weight made up of muscle, that person will require more Calories. This is down to the way the body works – muscle basically uses more Calories to simply exist.

To put it simply, if you consume more Calories than your body needs, the body will process the extra energy and store it as fat. If you consume less Calories than your body needs, your body will go to your fat stores and start using that fat as an energy source to make up the difference. While this might be good thing if you have a little excess fat you need to get rid of, it needs to be done in a controlled manner – extreme calorie restriction can damage your body and more often than not does not result in sustained weight loss, as when you invariably go back to a ‘normal’ Calorie intake, all the weight goes back on.

Online calculators can give you an estimate, but everyone is unique in their Calorie requirements. That might seem a bit overwhelming – like ‘how am I ever going to lose weight if I don’t actually know how many Calories I should eat’ – but in my humble opinion the best way to do that is to understand how Calories work, understand the food you’re eating, and understand the amount of movement you do in a day. From that you can develop a positive relationship with food and your body without counting every.last.thing you put in it.

So a calorie is the same regardless of what food it’s from?

Technically yes, because the Calorie is a measure of energy. So one Calorie provided by a chocolate bar is the same amount of energy as one Calorie provided by an apple.

So the people telling you that all you have to do to lose weight is be in a calorie deficit (i.e. consume less energy than your body requires each day) are correct. If you’re eating less calories than your body burns your body will turn to its stored fat for energy and you *should* lose weight.

BUT…

There’s a much, much bigger picture… it’s so much more complex than that. Firstly, and without wishing to overcomplicate matters, the amount of calories listed as being contained in a food might not be the amount the body actually gets. Remember how I spoke about the body using Calories just to exist? Well it uses energy to digest and process food. And foods are digested and processed by the body in different ways. So chocolate is easily processed by the body, so it might take 5 Calories to digest. So from 100 Calories you have 95 left, right? That’s 95 Calories worth of energy that the body needs to either use or store as fat. However if you eat chicken, its much more difficult to digest, so the body might need to use 20 Calories of the 100 to process it. So you’re left with 80 to either store or use. Make sense? So just because a packet says 100 Calories, the foodstuff makes a difference as to what your body actually ends up with.

Yes, you could meet your Calorie “goal” by only eating chocolate bars. You could eat chocolate morning, noon and night and as long as you stayed under your Calorie requirement, the theory is that you would lose weight.

But you’re going to feel absolutely rotten, eh?

The food you eat has so much more of an impact than simply providing Calories. If you only ate chocolate, your body would not be receiving the necessary vitamins and minerals it needs to work properly. Your hormone levels would be impacted. Your energy levels would peak and trough through the day. You’d probably get cravings when your blood sugar dropped. While the example of only eating chocolate is extreme, it illustrates that there’s a lot more to food consumption than simply Calories. For example, the way your body breaks down Calories depends on the type of food they come from. It’s so much more complex than simply energy in v energy out. This is why looking at food solely in terms of Calories is not a great idea.

Have a look at some of my other posts for deeper explanations of this.