Food Energy

One Calorie is the amount of energy (heat) to raise the temperature of one gram of water one degree Celsius. The magnitude of human energy requirements makes it awkward to use such a small unit, so the convention of the capitalized Calorie is equal to 1000 lowercase calories, and is abbreviated kcal to indicate that is 1000 times as large as the calorie.

The s and Sugar s have particularly high values for food energy. One Calorie is approximately equal to 4.1868 kilojoules.

MEASURING FOOD ENERGY

In the early twentieth century, the United States Department of Agriculture ( USDA ) developed a procedure for measuring food energy that remains in use today.

The food being measured is completely burned in a Calorimeter so that the Heat released through Combustion can be accurately measured. This amount is used to determine the gross energy value of the particular food. This number is then multiplied by a Coefficient which is based on how the human body actually digests the food.

For example, pure sugar releases about 3.95 kilocalories per gram (16.5 kJ/g) of ''gross energy'' but the digestibility coefficient of sugar is about 98% in humans, so the ''food energy'' of sugar is 0.98 × 3.95 = 3.87 kilocalories per gram (16.2 kJ/g) of sugar. Note, the digestibility coefficient is likely to vary between individuals based on genetic predisposition, and possibly may be affected by state of physical fitness of the individuals measured, but the mean digestibility for most people is around 98%.

NUTRITION AND FOOD LABELS

The "calorie" has become a common household term, because Dietitian s recommend in cases of Obesity to reduce body weight by increasing exercise (energy expenditure) and reducing energy intake. Many governments require food manufacturers to label the energy content of their products, to help consumers control their energy intake. In Europe , manufacturers of prepackaged food must label the nutritional energy of their products in both kilocalories ("kcal") and kilojoules ("kJ"). In the United States , the equivalent mandatory labels display only "calories" (meaning kilocalories); an additional kilojoules figure is optional. The energy content of food is usually given on labels for 100 g and for a typical service size.

The amount of . Instead, standardized chemical tests and an analysis of the recipe are used to estimate the product's digestable constitutents ( Protein , Carbohydrate , Fat , etc.). These results are then converted into an equivalent energy value based on a standardized table of energy densities:

Other substances found in food (water, non-digestable fibre, minerals, vitamins) do not contribute to this calculated energy density.

Recommended daily energy intake values for young adults are: 2500 kcal/ D (10 MJ/d, 120 W) for men and 2000 kcal/d (8 MJ/d, 100 W) for women. Children, sedentary and older people require less energy, physically active people more.

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REFERENCES

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