Calories and Kilojoules

Counting calories is a popular weight loss strategy, which is widely used. But what does the term denote? What’s the difference between calories and kilojoules? When nutrition value is stated, Calories are converted to kilojoules – are Calories and kilocalories the same? Read on to find it out.

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There are 5 terms related to food energy content, namely joule, kilojoule, calorie, kilocalorie and Calorie (yes, it’s not a slip of the keyboard – the first letter of the latter is capitalized). The confusion between the terms is mostly due to their belonging to different areas.

A note on physics

Joule is a unit of energy measure, which is sometimes confused with calories. A calorie is the term used to denote the energy amount that is required for heating water, or the energy that can raise the temperature of 1 g of water by 1 degree. This amount is roughly 4,18 joules, or, if converted, 4.18 kilojoules. The confusion stems from the tradition to define nutrition value in Calories (the first letter is a capital one); one “nutritional” Calorie is 1,000 common calories. That is why most labels state Calories, not calories or kilocalories – while technically it is kilocalories. These two kinds – calories and Calories – are sometimes called small and large calories respectively.

Are all calories the same?

The reason people eat is that food provides them with the energy their body needs to function. Proteins, fats and carbohydrates – the key elements of food – provide different amounts of energy. Proteins grant 4 Cal per 1 g, and fat and carbs’ energy supply may vary depending on what kind of food it is. The average figures are 9 Cal for fat, and 4 Cal for carbohydrates.

The human metabolism remains an aspect of body functioning that still has a lot of riddles to offer. While the energy a particular kind of substance can provide was measured in laboratories, it appears that the body processes these chemicals in a different way, and their actual nutritional value may well be different from that of the one mentioned on the label.

Nutrient type affects the speed at which it is processed, and a classic example is fats: while saturated fats are easily stored and more difficult to use as a source of energy, polyunsaturated fats – with omega-3 fatty acids hailed as the healthiest ones – are easier for the body to use when exercising.

As far as diet adjustments in patients with certain diseases are concerned, there is another thing of paramount importance, and that is the glycemic index, abbreviated as GI. Carbohydrates are broken down into sugars at different speeds, and those that are processed slower have a lower GI. Those suffering from diabetes are recommended to consume food that has low GI.

Basically, not all calories are the same, as it may be more or less difficult for the body to process food depending on what kind of food it is.

How many joules are there in 1 kg of body fat?

Our optimal calorie intake is shaped by a variety of factors, including gender, age, pregnancy, diseases, physical activity, etc. If we exceed the recommended calorie intake limit, we put on weight. You can use this calculator or some other one to find out what daily intake is considered a norm in your case.

1 kg of body fat equals about 37,000 kilojoules. That is why if you want to lose weight fast, the things you will lose will be water, muscles and some fat. Losing weight is a gradual process that takes time; otherwise there may be unwanted consequences – to say nothing of the eager-to-return pounds. Actually, as far as calories and weight loss are concerned, it’s not how much you eat that matters, but what you eat. And remember – the more muscles you have, the more calories you need; that’s why athletes can eat more without dealing a blow to their hopes of staying in shape: there’s physical activity combined with more muscles.


Calorie Calculator – Daily Caloric Needs –
Low-Carbohydrate Diets –
Kilojoules and calories –

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