A calorie is a unit of energy. In nutrition and everyday language, calories refer to energy consumption through eating and drinking, and energy usage through physical activity. For example, an apple may have 80 calories, while a 1 mile walk might use up about 100 calories.There are two types of calories:
- A small calorie (sympbol: cal) - 1cal is the amount of energy required to raise one gram of water by one degree Celsius.
- A large calorie (symbol: Cal, kcal) - 1Cal is the amount of energy required to raise one kilogram of water by one degree Celsius.
1 large calorie (1kcal) = 1,000 small calories.
In this article we will discuss what a calorie is, how many calories humans need on a daily basis and some other important facts about calories.
Contents of this article:
Fast facts on calories
Here are some key points about calories. More detail and supporting information is in the main article.
- A calorie is a unit of energy
- Calories are essential for human health; the key is taking on the right amount
- Everyone requires different amounts of energy per day depending on age, size and activity levels
- More than 11% of Americans' daily calories come from fast foods
- "Empty calories" describe foods high in energy but low in nutritional value
- Solid fats are so called because they are solid at room temperature
- Foods such as ice cream and bacon contain the most empty calories
- Americans consume an average of 336 calories per day from sugary beverages alone
- More than 50% of Americans have at least one sugary drink per day.
What are calories?
Anything that contains energy has calories in it, even coal.
Most people only associate calories with food and drink, but anything that contains energy has calories. For instance, one ton of coal contains the equivalent of 7,004,684,512 calories.
The terms large calorie and small calorie can be confusing, and to add further confusion, are often mistakenly used interchangeably. This article focuses on calories associated with foods, drinks and human energy expenditure (our burning up of energy).
According to Medilexicon's medical dictionary, a Calorie is "a unit of heat content or energy. The amount of heat necessary to raise 1 g of water from 14.5-15.5°C (small calorie). Calorie is being replaced by joule, the SI unit equal to 0.239 calorie."
The calories included in food labels are, in fact, kilocalories - units of 1,000 small calories. Therefore, a 250-calorie chocolate bar is actually 250,000 calories.
Calories and human health
The human body needs calories to survive, without energy our cells would die, our hearts and lungs would stop, and we would perish. We acquire this energy from food and drink.
If we consume just the number of calories our body needs each day, every day, we will probably enjoy happy and healthy lives. If our calorie consumption is too low or too high, we will eventually experience health complications.
The number of calories food contains tells us how much potential energy they posses. Below are the calorific values of the three main components of the food we eat:
- 1 gram of carbohydrates contains 4 calories
- 1 gram of protein contains 4 calories
- 1 gram of fat contains 9 calories.
Let's look at where the calories in one cup of large eggs (243 grams) come from:
- Fat 24 grams.
24 x 9 = 216 calories.
- Protein 31 grams.
31 x 4 = 124 calories.
- Carbohydrate 2 grams.
2 x 4 = 8 calories
- 243 grams of raw egg contain 348 calories, of which 216 come from fat, 124 from protein and 8 from carbohydrate.
How many calories do we need each day?
Not everybody requires the same number of calories each day. Our ideal calorific consumption depends on several factors, including our overall general health, physical activity demands, sex, weight, height, and shape. A 6ft tall, 25-year-old professional soccer player needs many more calories each day than a 5ft 4ins sedentary woman aged 75.
Health authorities around the world find it hard to agree on how many calories their citizens should ideally consume. The US government says the average man requires 2,700 calories per day and the average woman 2,200, while the NHS (National Health Service), UK, says it should be 2,500 and 2,000 respectively.
The FAO (Food and Agriculture Organization) of the United Nations says the average adult should consume no less than 1,800 calories per day.
On the next page, we look at the importance of timing meals, compare calories and joules and discuss empty calories.