What Are Calories? How Many Do We Need?

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 (symbol: 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.

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 the food contains tells us how much potential energy they possess. 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 a raw egg contains 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.

When you eat is important

A large breakfast helps control body weight – researchers from Tel Aviv University wrote in the journal Obesity that a big breakfast – one containing approximately 700 calories – is ideal for losing weight and lowering your risk of diabetes, heart disease, and high cholesterol.

Team leader, Prof. Daniela Jakubowicz stressed that when we eat our food matters as much as what we eat.

Calories or Joules?

In many regions, including the European Union, Australia and New Zealand, it has become standard practice to include energy data in food labels in joules (kilojoules) instead of kilocalories (calories). In the United States, most food labeling is done in calories.

1 joule = 0.239005736 of a calorie, or 1 calorie = 4.18 joules.

This can be confusing and irritating if you live in a country where the food labeling is done in joules, but all exercise programs, diet regimes and health topics regarding energy consumption talk in calories. Fortunately, most food labels in the European Union also add calorie-equivalent information.

Fast food in American diets

On average, Americans eat too much fast food.

Researchers from the CDC (Centers for Disease Control and Prevention) published a report in February 2013, showing that 11.3% of people’s calories in the US come from fast foods.

Even though the figures are an improvement, nutritionists and health care professionals say it is still too high.

As people get older, they tend to get fewer of their daily calories from fast foods, the authors explained. Fast foods only made up 6% of seniors’ daily calorie intake.

They also found that non-Hispanic white people and Hispanic adults consume less fast food than black adults.

Many fast food restaurants serve meals that have calorie-counts much higher than the daily recommended amounts.

What are empty calories?

Empty calories, also known as discretionary calories are those we consume with very little nutritional value, they possess virtually no dietary fiber, amino acids, antioxidants, dietary minerals or vitamins.

According to ChooseMyPlate.gov, a part of the USDA, empty calories come mainly from solid fats and added sugars.

    • Solid fats, such as beef fat, shortening and butter, are solid when at room temperature. Although solid fats exist naturally in many foods, they are commonly added during industrial food processing, as well as when certain foods are being prepared.


  • Added sugars – these are calorific sweeteners that are added to foods and beverages during industrial processing. In the USA, the most common types of added sugars are sucrose and high-fructose corn syrup, which are mainly composed of about half fructose and half glucose.

Added sugars and solid fats are said to make foods and drinks more enjoyable. They are added by food and beverage companies to boost sales. However, they also add many calories and are major contributors to the obesity epidemic.

According to ChooseMyPlate.gov, the following foods and drinks have the most empty calories in the United States:

  • Solid fats + added sugars
    – ice cream
    – donuts
    – pastries
    – cookies
    – cakes
  • Solid Fats
    – ribs
    – bacon
    – hot dogs
    – sausages
    – cheese
    – pizza
  • Added Sugars
    – fruit drinks
    – sports drinks
    – energy drinks
    – sodas.

There are ways of purchasing the above-mentioned products, or similar ones, with less solid fat or empty sugars. Rather than going for the standard hot dog or a fatty cheese, one could choose a low-fat cheese or low-fat hot dog.

Americans consume too many empty calories – Americans consume 336 calories per day from just sugary beverages, the CDC reported in 2011. According to the American Heart Association, sugar from drinks should not exceed 450 calories per week.

More than half of all Americans have at least one sugary drink each day. Approximately 5% of people aged two years or more in the USA consume at least 567 calories per day from sugary drinks, i.e. more than four cans daily.

Rachel Johnson, from the American Heart Association, says:

Sugar-sweetened beverages are the number one single source of calories in the American diet and account for about half of all added sugars that people consume.

Most Americans don’t have much room in their diets for a completely nutrient void beverage. One recent study showed that drinking more than one sugar-sweetened beverage a day increases your risk of high blood pressure.

It’s better if you can avoid them altogether and instead consume water, fat-free or 1% fat milk, 100% fruit juice and low-sodium vegetable juices.”