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Introduction to Calories

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 may 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 . 

Most people associate calories just with food and drink, but anything that contains energy has calories. One ton of coal contains the equivalent in energy 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.

Why are calories important for human health? 

The human body needs calories (energy) 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 foods contain 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.

Lets 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.

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.

How many calories should I eat a day?

The number of calories you should eat each day depends on several factors, including your age, size, height, sex, lifestyle, and overall general health. A physically active 6ft 2in male, aged 22 years, requires considerably more calories than a 5ft 2ins sedentary woman in her 70s.

It has been discovered that even factors such as how you eat your food can influence how many calories get into your system. The longer you chew your food, the more calories the body retains, a team from Purdue University found.

Recommended daily calorie intakes vary across the world. According to the National Health Service (NHS), UK, the average male adult needs approximately 2,500 calories per day to keep his weight constant, while the average adult female needs 2,000. US authorities recommend 2,700 calories per day for men and 2,200 for women.

It is interesting to note that in the UK, where people on average are taller than Americans, the recommended daily intake of calories is lower. Rates of overweight and obesity among both adults and children in the USA are considerably higher than in the United Kingdom.

The NHS stresses that rather than precisely counting numbers (calories), people should focus more on eating a healthy and well balanced diet, being physically active, and roughly balancing how many calories are consumed with the numbers burnt off each day. If you eat your five portions of fruit and vegetable per day you will probably live longer, Swedish researchers reported in the American Journal of Clinical Nutrition (July 2013 issue).

According to the United Nation’s Food and Agriculture Organization (FAO), the average person’s minimum calorie requirement per day globally is approximately 1,800 kilocalories (7,500 kJ).
Daily calorie consumption varies considerably around the world
Daily calorie consumption varies considerably around the world
(countries in gray indicates “no data available”)

Over the last twenty years, sugar has been added to a growing number of foods we consume. Unfortunately, food labels in the USA and Europe do not include details on how much added sugar there is . Dr Aseem Malhotra, a cardiologist, wrote in the BMJ (British Medical Journal) in June 2013 that “(it has become) almost impossible for consumers to determine the amount of added sugars in foods and beverages.”

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.

Fast facts on daily calorie intake:

Here are some key points about daily calorie intake. More detail and supporting information is in the main article.

  • Recommended calorie intake depends on factors such as age, size, height, sex, lifestyle and overall general health.
  • The longer you chew your food, the more calories your body retains.
  • US authorities recommend 2,700 calories per day for men and 2,200 for women.
  • A big breakfast helps bring your weight down or keep it down.
  • When we eat our food probably matters as much as what and how many calories we eat.
  • In industrialized nations and a growing number of emerging economies, people are consuming many more calories than they used to. Portion sizes are far greater today.
  • For the human body to remain alive, it requires energy. Approximately 20% of the energy we use is for brain metabolism.
  • Ideal body weight depends on several factors including age, sex, bone density, muscle-fat ratio and height.
  • Not all calories are the same, not all diets are the same. Simply counting calories, and ignoring what you put in your mouth might not lead to good health.
  • A 500-calorie meal of fish/meat, salad, and some olive oil, followed by fruit, is much better for your health and will keep you from being hungry for longer than a 500-calorie snack of popcorn with butter or toffee. 

Calories or Joules?

In many countries, such as 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.

In developed countries like US   11.3% of people’s calories 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.

What are “Empty Calories”?

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

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 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.