Everything we consume contains energy that our bodies use to move, grow and stay healthy. To know how much energy is in different foods and drinks, we first need to review some core concepts.
First, you’ve probably heard of the calorie, a unit of measure for energy, and its metric equivalent, the joule. A calorie is defined as the amount of energy required to raise the temperature of 1 gram of water by 1°C.
In human nutrition, the amount of energy required to keep you healthy and fuel your body is far more than the minute amount of calories used to heat 1 gram of water. Therefore, the term “calorie” in nutrition refers to a kilocalorie (or kcal), which is generally 1,000 calories. When you see the word “calorie” on a Nutrition Facts label, it probably refers to kcal.
Energy stored in food and drink is released when the body breaks down one or more of the four macronutrients in food (carbohydrates, proteins, fats and alcohols). The body then uses that energy for activities such as beating the heart, breathing the lungs, and maintaining muscle movement.
When estimating energy in food, it is the amount of energy a food or drink provides for these bodily processes. The four macronutrients provide different amounts of energy.
- 1.1 gram of carbohydrates provides about 4 kcal of energy.
- 2.1 gram of fat provides approximately 9 kcal of energy
- 3.1g of protein provides about 4kcal of energy.
- Four.One gram of alcohol provides about 7 kcal of energy.
How are calories estimated?
There are two ways to estimate the energy content of food and drink.
The first is called “bomb calorimetry”. This most standard method involves placing a small sample of food or drink in a device known as a bomb calorimeter. Food burns in the presence of oxygen, giving off heat.
The amount of heat released is directly related to the energy content of the food, so calculations are possible. This method is most commonly used for fat-rich foods and is considered the most reliable (but expensive) method.
The second method, the Atwater system, is a much cheaper method for estimating energy content. It is often used when calculating the energy of most foods and beverages sold in supermarkets. Named after legendary food researcher Wilbur Atwater, the system uses standard conversion factors for each macronutrient found in food and beverages. By estimating the amount of each of the four macronutrients, a rough calculation of total energy can be made.
However, this method requires detailed knowledge of the ingredients of complex foods (such as muesli bars and hamburgers) and can be less accurate. Also, the Atwater system assumes that the composition of each component is always the same, so a margin of error is to be expected.
For example, due to climate and soil differences, a cup of oats grown in one part of the country may not have exactly the same nutritional composition as another cup of oats grown elsewhere. not. Therefore, this system is an estimate based on averages.
The key is to estimate the energy content of food and drink with both methods. However, the actual energy our bodies extract from these foods and beverages varies depending on factors such as individual differences in digestion and absorption, and how the food is processed and prepared.
Why are calories written on food?
In Australia, it is legally required to have nutrition information panels displaying the number of calories in packaged foods.
However, homemade food products sold at wet markets and elsewhere may not be required to provide a Nutrition Facts panel. This depends on the type of food you sell and the size of your business.
Perishable foods such as fruits, vegetables, and meats also do not require nutrition information panels. To find out how many calories you have, you can either run an experiment with a bomb calorimeter or look up estimates in online nutrition databases.
Food composition databases such as CalorieKing compile information on the energy and nutrient content of various foods. Nutritionists and other medical professionals often use these databases to estimate the energy content of foods and inform dietary recommendations.
various international standards
Both kJ and kcal refer to energy. They are just two different units of measurement (such as inches and centimeters being two different units of measuring length). The kilojoule (kJ) is part of the International System of Units (SI).
kJ is used in Australia, New Zealand, and some parts of Europe. US and UK use kcal. To convert between calories and kilojoules, use the following conversion factors:
- 1 kcal = 4.184 kJ
- 1 kJ = 0.24 kcal (about a quarter).
For example, if you have a packet of potato chips with an energy content of 200 kcal, you can convert it to kJ as follows: 200 kcal × 4.184 = 836.8 kJ.
As for how many calories you can eat, the Australian Healthy Eating Guidelines estimate that the average adult needs about 7,000kJ or 1,670Kcal each day. However, differences in age, gender, size, health status, and physical activity affect the amount of energy a person needs.
To estimate your personal energy requirements, you can use this Nutrient and Dietary Energy Calculator.
Lauren Ball is Professor of Community Health and Human Services at the University of Queensland. Emily Burch is a nutritionist, researcher, and lecturer at Southern Cross University. Katelyn Barnes is a Postdoctoral Fellow at the University of Queensland’s School of Human Exercise and Nutrition Sciences. This work was first published in The Conversation.
