Calories are units of energy. In nutritional terms, they refer to the amount of energy that an individual consumes via food & drink and the energy he or she expends via physical activity.
A ‘calorie’ or ‘cal’ (with a lowercase c, also referred to as a small calorie) is the amount of energy required to raise the temperature of 1 gram of water by 1 degree Celsius.
A ‘kilocalorie’ or ‘kcal’ or ‘Calorie’ (with an uppercase c, also referred to as a large calorie) is the amount of energy required to raise the temperature of 1 kg of water by 1 degree Celsius.
1000 calories = 1 Calorie = 1 kilocalorie
Most food labels and nutrition websites will provide energy information in kcal. For example, a medium sized apple has around 95 kcal, or 95,000 calories. To keep things simple however, nutritionists (and a lot of websites) tend to use the word calories to represent kilocalories.
So in essence, if you hear someone say “I eat 2000 calories a day“, what they really mean is “I eat 2000 kilocalories a day”.
You may have also noticed that food labels provide information in kilojoules (kJ). Joules are just another way to measure energy (similar to how both kilometres and miles can be used to measure distance).
1 kcal = 4.184 kJ
Where do calories come from?
If you studied biology in high school, you will recall a process called photosynthesis, where plants convert sunlight into chemical energy. Water and carbon dioxide are used to synthesise this chemical energy, which is stored in carbohydrate molecules. Plants can then create protein and fat molecules using these carbohydrate molecules.
Plants provide herbivores with a source of energy, which in turn provide carnivores with their energy. Human beings obtain their energy from both plant and animal based food sources.
Many of the foods that you eat contain carbohydrates, proteins, fats, water, vitamins and minerals. However, only the carbohydrates, protein and fat, also known as macro-nutrients, provide you with calories.
Water, vitamins and minerals provide no calories, but they are needed for our bodies to be able to make use of the calories stored in the macro-nutrients.
Proteins and carbohydrates have 4 calories (i.e. kcal) per gram whereas fats have 9 calories per gram. This is why the number of calories in foods can vary significantly.
For example, 100 g of almonds provide you with 575 calories because they have 49 g of fats, 22 g of carbohydrates, 21 g of protein and 5 g of water.
On the other hand, 100 g of bananas provide you with 89 calories because they have almost no fats, 22 g of carbohydrates, 1 g of protein and 75 g of water.
Foods that contain large amounts of fat (such as nuts and seeds) will have far more calories than those that have large amounts of water (such as vegetables and fruits).
It is quite difficult to accurately determine how many calories a certain food has off the top of your head. Luckily, there are tools that will provide this information for you.
Two examples are the website nutritiondata.self.com and the app myfitnesspal. You can also use our food finder tool to compare the nutritional information of over 100 healthy foods.
How many calories should you be eating?
Energy requirements vary from person to person and are dependent on a number of factors.
- Age – in general, the older a person gets, the fewer calories they will need. This is because our metabolism begins to slow down as we age.
- Body size and composition – the larger and more muscular a person, the more calories he or she will need. Men tend to have larger bodies and more muscle mass than women, and therefore require more calories.
- Activity levels – the more active a person, the more calories they burn. An individual who works out 6 times a week and leads an active lifestyle will need far more calories than someone who sits most of the day and does no exercise.
- Overall goals – if you want to lose weight, you need to consume fewer calories than you burn. This caloric deficit will force your body to utilise its fat stores as a source of energy. If on the other hand you want to gain weight (particularly muscle mass), you need to consume more calories than you burn (including sufficient amounts of protein), and accompany this with regular exercise.
It is extremely difficult to calculate with 100% accuracy the calorie requirements of an individual. However, there are a number of algorithms that have been formulated over the years to do this as precisely as possible. An example is the Mifflin-St Jeor formula, which is thought to be one of the most accurate.
To spare you the hassle of having to manually use the formula, we have created the easy to use tool below. Simply enter your details and click Calculate.
This calculator will never show a number below 1000 calories per day. Please speak to a qualified health professional before attempting to eat less than that.
For example, a 30 year old lady who weighs 130 lb (59 kg), is 5 feet 8 inches tall and exercises 4 times a week should aim to consume approximately 2100 calories to maintain her weight and 1700 calories to start losing weight.
It is important to keep in mind that even though two foods have the same number of calories, they may affect your appetite and metabolism differently. For example, a can of cola has around 150 calories, as do two large boiled eggs. But eating the eggs will keep you feeling satisfied for much longer than the cola will.
The majority of your diet should consist of foods that have undergone very little processing; these are the ones that are as close to their natural state as possible, meaning they are rich in vitamins & minerals. This includes vegetables, fruits, legumes, nuts, seeds, fish and unprocessed meats.
The foods that you want to limit intake of are those that have been highly processed. These foods tend to contain large amounts of hydrogenated fat and and / or sugar but are lacking in protein, fiber, vitamins and minerals. They are a source of what are known as ‘empty calories‘. Examples of these foods include cakes, candy, sugar, potato chips and sugar sweetened beverages.