What is the test to investigate the amount of energy in food?

December 12, 2025 •

3 min read

Did you know that the gold-standard test to investigate the amount of energy in food involves burning a sample in a high-pressure, oxygen-filled chamber? This scientific process, known as bomb calorimetry, is crucial for determining the total or gross energy value of food products.

Quick Summary

Bomb calorimetry is the primary method for investigating food energy by measuring heat released from combustion. The Atwater system is an alternative calculation method used for nutritional labels, based on a food's macronutrient composition.

Key Points

Bomb Calorimeter: The most accurate and definitive test for food energy, measuring the total heat released through combustion in an oxygen-filled chamber.
Atwater System: The method used for food labeling, which indirectly calculates metabolizable energy using average conversion factors for macronutrients.
Gross vs. Metabolizable Energy: Bomb calorimetry measures the total or gross energy, while the Atwater system provides the metabolizable energy, which is what the body can actually use.
Classroom Calorimetry: A simplified experiment using basic equipment to demonstrate the concept of energy release, though it is far less accurate due to heat loss.
Food Labels: Nutritional information on packaged food is derived from Atwater calculations, not direct calorimetry, because it better reflects the energy available to the human body.

The Definitive Laboratory Method: Bomb Calorimetry

Calorimetry is the scientific process of measuring the heat released or absorbed during a chemical reaction or physical change. For determining the energy content of food, the most accurate laboratory method is bomb calorimetry. This technique involves using a device called a bomb calorimeter, where a dried food sample is completely combusted in a sealed, oxygen-rich chamber. This provides a precise measurement of the total chemical energy, also known as gross energy.

How a Bomb Calorimeter Works

A bomb calorimeter consists of a sealed, steel vessel (the 'bomb') containing the food sample and a pure oxygen atmosphere. This bomb is submerged in a known amount of water within an insulated container. An electrical wire ignites the sample, causing it to burn. The heat released warms the surrounding water. A thermometer measures this temperature change. The energy released by the food is calculated using the mass of water, its specific heat capacity, and the temperature change.

The Process of Bomb Calorimetry

Accurate bomb calorimetry involves several steps:

Sample Preparation: The food is homogenized and dried to remove moisture.
Weighing: A precise mass of the prepared sample is weighed.
Combustion: The sample is burned completely in the calorimeter.
Measurement: The maximum water temperature is recorded.
Calculation: The heat transferred to the water is calculated to find the energy per gram of food.

The Atwater System: Indirect Calculation for Food Labels

Bomb calorimetry measures total potential energy, but doesn't account for digestion losses. Food labels typically use the Atwater system, an indirect calculation based on average energy conversion factors for protein, fats, and carbohydrates.

Comparing Energy Values: Gross vs. Metabolizable

Bomb calorimetry measures Gross Energy (total heat from combustion). The Atwater system calculates Metabolizable Energy, which is available to the body after accounting for losses during digestion. For example, indigestible fiber's energy is measured by bomb calorimetry but excluded by the Atwater system. The Food and Agriculture Organization (FAO) provides standardized factors for metabolizable energy calculations.

Simplified Classroom Calorimetry

A basic calorimetry experiment can be done using a food sample and water, ignited by a Bunsen burner. While this demonstrates the principle, it's much less accurate than a bomb calorimeter due to significant heat loss.

Modern Nutritional Analysis

Bomb calorimetry is used in creating food composition databases. Food labels use the Atwater system's values, which are more relevant to human digestion. For new foods, direct calorimetry and chemical analysis establish energy values. The FAO is an authoritative source for food energy conversion details.

Comparison Table: Bomb Calorimeter vs. Atwater System


Feature	Bomb Calorimeter	Atwater System
Method	Direct measurement of combustion heat	Indirect calculation based on macronutrients
Energy Measured	Gross energy (total heat released)	Metabolizable energy (digestible by the body)
Application	Scientific research, food databases	Standard food labeling, dietary analysis
Cost	High (expensive, specialized equipment)	Low (calculation based on composition)
Accuracy	High precision, measures total potential energy	Lower accuracy, based on average digestibility factors

Conclusion

The test to investigate the amount of energy in food depends on the need. Bomb calorimetry is the accurate lab tool for total energy measurement. The Atwater system is a practical, indirect method for food labeling, reflecting metabolizable energy. Simplified experiments are for education, but professional analysis is precise and standardized.

Frequently Asked Questions

The bomb calorimeter is the most accurate laboratory method for determining the total energy content of food. It measures the gross energy released when a food sample is completely burned in a controlled environment.

The calorie count on a food label is typically determined using the Atwater system. This method uses standardized energy conversion factors (e.g., 4 kcal/g for protein and carbohydrates, 9 kcal/g for fat) to calculate the energy based on a food's macronutrient composition, rather than direct burning.

Gross energy is the total energy released during the complete combustion of food, as measured by a bomb calorimeter. Metabolizable energy, calculated by the Atwater system, is the portion of that energy that is actually available for the human body to use after digestion and absorption.

Bomb calorimetry measures all energy, including that from indigestible components like fiber. The Atwater system is preferred for food labels because it provides a more realistic estimate of the metabolizable energy that the human body can actually extract from the food.

While a simplified version of a calorimetry experiment can be done in a classroom or laboratory setting, it is not recommended for home use due to the high risk of fire and inaccurate results. These experiments often have significant heat loss, making the calculated energy values unreliable.

The standard international unit of energy is the joule (J). In nutrition, energy is also commonly expressed in kilocalories (kcal) or 'food Calories' (Cal), where 1 kilocalorie equals 4.184 kilojoules.

The primary macronutrients that provide energy are carbohydrates (approx. 4 kcal/g), fat (approx. 9 kcal/g), and protein (approx. 4 kcal/g). Alcohol also provides energy (approx. 7 kcal/g).