What is a Calorie?

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If you have any interest in dieting (and presumably you do, if you're reading this), you've almost certainly come across the word "calorie". Maybe you have an idea what it means - in particular, you probably have the impression that too many calories aren't good. But what exactly is a calorie, and how do calories relate to healthy eating and your weight?

Definition of a calorie: a unit of energy

Calories measure energy, especially heat energy. One calorie is the energy required to raise the temperature of one gram of water by one degree Celsius.

In the past, the calorie was used in fields such as engineering, but now you'll only ever hear "calorie" use in reference to food energy - it's considered archaic in other contexts.

The metric equivalent of the calorie is the joule, and some countries (such as Australia) have this as their food energy unit. It's easy to convert calories to joules: there are 4.2 joules in every calorie.

Difference between calories and kilocalories

One calorie is a tiny amount of energy - so the "calories" referred to on food packaging and in diet plans are in fact "kilocalories" (also referred to as Calories - with the capital C). With metric measurements, "kilojoules" (kJ) are always used.

From this point onwards, when you see the word "calorie", I'm discussing kilocalories.

Calories in and calories out

There are two ways in which you might want to track calories: one is how many you consume - how much energy you take in. The other is how many calories you "burn" during exercise - how much energy you put out.

If you eat more calories than you need (for normal metabolic functions and for the activity which you do), then your body will store the extra energy as fat. If you eat fewer calories than you need, your body will burn fat to provide the extra energy.

How many calories should I be eating?

In the UK, the recommended daily calorie intake is 2,000 calories per day for women and 2,500 for men. However, the government is currently reviewing this - suspecting that our sedentary lifestyles mean that fewer calories are needed in order to maintain a healthy weight.

If you're trying to lose weight, most nutritionists recommend a calorie range between 1,200 and 1,800 for optimum weight-loss. The more overweight you are to start with, the more calories you can eat - as heavier bodies need more energy just to function. This handy calorie calculator lets you figure out your personal calorie needs.

You shouldn't drop below 1,100 calories, and certainly not for an extended period of time.

One word of warning - try not to get too hung up on just counting calories in what you eat. There are plenty of foods that are low-calorie but of questionable nutritional value - such as many "lite" or "low" ranges. Yes, calories matter, as they allow the energy provision of different foods to be compared - but they are by no means the only factor to consider for a successful diet.

More like this in Science · Jul 25, 2008

17 Comments

Steve Parker, M.D. on 07/25/08

Nearly all successful popular diets reduce caloric intake below baseline, whether or not they have you actually count calories or not. This is true of the Atkins diet, for example.

-Steve

The Health Blogger on 07/27/08

This is very true, any diet in which one desires fat loss always advocates the calorie deficit route.

It's very interesting you wrote about this topic, a few years ago I came across Aktivated Barley, which apparantley provides over 400% more energy per calorie than any other food calorie known.

This barley registers between 100,000 to 320,000 on the Bovis Scale.

Thought this may be of interest to all.

NeoVitin on 07/25/08

Thanks for taking the time to clarify this. Decreasing caloric intake is the first step towards weight-loss, but I believe it is important to monitor calories while still eating nutritious foods, instead of eating just less of unhealthy foods.

Yongho Shin on 07/25/08

This is the best straight-to-the-point, honest article I've seen on calories. Great post!

Spectra on 07/25/08

For some reason, reading this article takes me back to my physical chemistry class in college where we had to determine how many Calories are in a peanut. We burned a peanut in a calorimeter and measured how much hotter the water got. Since one calorie=the amount of energy required to heat one gram of water one degree Celsius, you can use that to figure out that there are roughly 3-4 Calories in a peanut.

Very informative article!

Ali from The Office Diet on 07/28/08

We did that too, Spectra (though I must confess I'd forgotton all about it when I read the article!) As far as I recall from my schooldays, the results weren't massively accurate -- it's hard to light a peanut. ;-)

Olaf on 07/26/08

thanks for the Informations, i was surprised that it should be not less than 1100 calories per day

Jeff on 07/26/08

Super! As a Naturalpath I am very pleased to see this proper, accurate & informative information being made available.
It's very consistent, although falls greatly short of complete that I offer on my WebSite free. I'm a healer 1rst, busiman 2nd.

Amazing stuff!
-Jeff D.Np

Jeff on 07/26/08

Post Script by Jeff D.Np.

Quote from my Mentor,

Dr. David Viscott once wrote " There is only 1 thing that causes overwright & thats over-eating."

Yes, there are the excuses of such things as 'Big Boned' 'Glandular Diseases' etc. (myth) that can also cause overweight These so called glandular diseases, well...let me put it this way, are less common that being hit by lightning 3X in a row in the same storm. Enough excuses? Let me put it to you this way, even if you suffer from a legitimate "glandular disease etc." wieght & excessive weight can't be achieved without excessive food consumption. Furthermore, as with most weight problems, diet & excersize are the answer to good and/or recovering health. This includes almost All diseases. Daily excersize and proper food consumption is the key for maintaining & restoring good health.

Bottom line for dieters and people suffering from obesity (newest western disease"
"If you really want to get rid of these unwanted LB's, LEAVE THEM ON THE PLATE! This will work & is the only answer, I promise you that!

Hoping Amazing success for all of you serious people who read this & other Sites!

Jeff
Peterborough, Ontario
Jeff_Scanlon@hotmail.com
Alternative Apothecary (Author)

Michael on 07/26/08

I most definatley agree that you should not just be concerned with the amount of calories, you also need to maintain a healthy and balanced diet while losing weight. Calories in and out is the basis of successful weight loss.

Paul on 07/27/08

I really agree with this comment "try not to get too hung up on just counting calories".

Eating a balanced diet rich in fruit and vegetables and low on junk food is far more important than counting calories.

One problem I've found when trying to count calories is that most food labels don't give the information your looking for and some (meat and cheese for example) usually don't have ANY information on calories.

Spectra on 07/27/08

Paul, I know what you mean. I eat mostly unprocessed foods and there isn't exactly a nutritional label on fruit, vegetables, eggs, meats, cheeses, etc. Because I eat mostly unprocessed foods like that, I don't focus too much on counting calories. But if I do want to know how many calories are in something, I'll look it up on www.fitday.com to get a rough estimate of what I'm eating in a day.

Gabrielle on 07/27/08

Thank you for this article, a lot of people use the term 'calorie' as a buzz word and don't know what it actually refers to.

jessiem on 07/28/08

A good lesson on calorie for all. Thanks

Charles on 12/ 2/08

I'm a fan of counting calories for a month or so just to get a perspective on how many calories are in certain foods.

But I will always argue that quality is just as important if not more important than quantity.

But I am also a fan of controlling caloric intake-- with high quality foods.

Gabrielle on 03/ 7/09

No one really has to go on a diet because all they have to do is exercise. So, anything could be eaten.

student on 04/14/09

Great information on calories Ali Hale, great job. It really helped with my project. Thanks!!!

What is a Calorie?

Definition of a calorie: a unit of energy