The energy we obtain from the food and drinks we consume is essential for our bodies to function properly. To determine the energy content of different foods and drinks, there are a few key concepts to consider.
Firstly, calories are the units of measurement for energy that you may be familiar with. Another metric equivalent is joules. A calorie is defined as the amount of energy needed to raise the temperature of 1 gram of water by 1?.
However, in human nutrition, the energy required to maintain health and fuel our bodies is much larger than a single calorie. Therefore, in nutrition, the term “calorie” commonly refers to a kilocalorie (kcal), which is equal to 1,000 calories. When you see “calories” on a nutrition label, it is likely referring to kcals.
The energy stored in food and drinks is released when the body breaks down the macronutrients present in them: carbohydrates, proteins, fats, and alcohol. This energy is then used for various bodily processes such as keeping our heart beating, our lungs breathing, and our muscles moving.
When estimating the energy content of food, it refers to the amount of energy that food and drinks provide for these bodily processes. The different macronutrients provide varying amounts of energy:
– 1 gram of carbohydrate provides about 4 kcal of energy
– 1 gram of fat provides about 9 kcal of energy
– 1 gram of protein provides about 4 kcal of energy
– 1 gram of alcohol provides about 7 kcal of energy
There are two methods used to estimate the energy content of food and drinks. The first is bomb calorimetry, which involves burning a sample of food or drink in the presence of oxygen to release heat. The amount of heat released is directly related to the energy content of the food. This method is most commonly used for foods rich in fats and is considered the most reliable but expensive method.
The second method is the Altwater system, which is a less expensive method used to estimate the energy content of most food and drinks sold in supermarkets. This method uses a standard conversion factor for each macronutrient found in food and drinks. By estimating the amount of each macronutrient, an approximate calculation of the total energy can be made. However, this method may be less accurate as it assumes each ingredient is always the same in composition.
Both methods estimate the energy content of food and drinks, but the actual energy our bodies extract from them can vary due to factors such as digestion, absorption, food processing, and cooking methods.
In Australia, it is a legal requirement for packaged food items to display the number of kcal they contain on a nutrition information panel. However, homemade food items sold at fresh markets may not be required to provide this information. Fresh foods like fruits, vegetables, and meat also do not require a nutrition information panel. To find out the energy content of these foods, you can either use a bomb calorimeter or refer to online nutrition databases.
Different countries use different units of measurement for energy. Australia, New Zealand, and parts of Europe use kilojoules (kJ), while the United States and the United Kingdom use kilocalories (kcal). To convert between calories and kilojoules, conversion factors are used.
For example, if a packet of chips has an energy content of 200 kcal, it can be converted to kJ by multiplying it by 4.184: 200 kcal × 4.184 = 836.8 kJ.
The Australian Guidelines for Healthy Eating estimate that the average adult requires about 7,000 kJ or 1,670 kcal per day. However, individual factors such as age, gender, size, health, and physical activity level will influence a person’s energy needs.
To estimate your personal energy requirements, you can use a nutrients and dietary energy calculator.