When reading labels on foods, you may be confused as to which units of energy to use, including Kilojoules, Metric energy, Atwater general factor system, NME, and calories. The following information will help you understand these terms and how to find the equivalent of a calorie in a given food. Also, if you’re trying to estimate how much energy is in your daily meals, you may find it useful to review the Codex Alimentarius’s general factors system, which specifies calorie intake in foods.

Metric energy

In the United States, food energy is expressed in calories. A calorie is the amount of heat required to raise the temperature of a gram of water by one degree Celsius. Kilocalories are a more modern unit of energy, and are abbreviated kcal. This system is more comparable to the units used for water temperature than to calories. While calories are the most widely used unit of energy, they are inaccurate for many different reasons.

The first time that food energy was measured in metric form was by Karl Voit, a German physiologist and the first person to create a laboratory for measuring energy levels in food. Although Voit would have been aware of Mayer’s work on the caloric equivalence of physical labor, he did not adopt the kg-calorie as a standard. Instead, he began using the g-calorie in his lectures in 1866. In his lecture, he stated that the daily metabolism of one male subject would be around 2.25 x 106 g-calories. Voit probably chose the g-calorie because his students already knew about Favre and Silbermann’s work.


Foods are measured in kilojoules, a unit of energy equal to 4.2 calories per 100g. Kilojoules are an easier way to understand than calories, and they are often used on food labels and official signs in Australia. Kilojoules are also used in the United States to help people understand the energy content of their food. Kilojoules are a more convenient way to understand energy in food, because they are easier to compare. Kilojoules are also easier to convert than calories, and they’re both related to maintaining a healthy weight.

For the average adult, you need about 8,700 kilojoules per day. That’s a figure that varies, as your body uses different amounts of energy. A typical Australian needs approximately 8,700 kJ of food per day for weight maintenance, but this number varies according to age, height, and physical activity. Kilojoules aren’t the same for everyone, so it’s important to read the labels before you purchase food.

Atwater general factor system

The Atwater general factor system is a widely used way to estimate food energy. It is based on the ‘4-9-4’ method, which applies energy conversion factors to protein, carbohydrates, fat, and alcohol. Foods are then summed to determine their calorific value. Alcohol is included as a macronutrient, and contains about 7 kcal per gram. The total energy per gram is equal to the ‘available energy’ of the food.

The Atwater general factor system is not entirely accurate. It consistently overestimates the ME content of diets that are low in fat and high in fiber. This is inconsistent with other studies. The Atwater system also does not account for fiber, which is partially degraded in the large intestine. Nevertheless, the conversion factor for fiber is usually 2 kcal/g. The Atwater method is the most widely used system today.


The energy contained in food is measured in terms of its kilocalorie content. Food energy can be expressed in two ways: in NME form and ME form. NME-1 factors are those applied to total protein, fat, and lactose/glucose. NME-2 factors assume that about 10 percent of protein is unavailable and that oligosaccharides are present. These factors are applied to all foods.

This form of measurement is also used to indicate the amount of dietary energy contained in a specific food. Although the two forms of energy are equivalent, they may differ in a number of ways. For example, some countries use energy values for novel ingredients, such as polyols and polydextrose. For example, the amount of calories in a serving of pasta is higher than that in a single serving.

The differences between ME and NME form are not so great. For example, in most mixed diets, 75 percent of the energy comes from fat and carbohydrate. While the Atwater general factor is lower than the NME factor, the energy from protein is similar. Fermentable fibre has a smaller NME value than nonfermentable fibre. For infants, the energy content of these foods is lower than that of general foods.