Fuel value, food

Food Fuel Value (kcal) Energy Output (kcal/min)... 

Food Fuel Value (kcal) Sitting (1.7 kcal/min) Walking (5.5 kcal/min) Cycling (10 kcal/min) Swimming (8.4 kcal/min) Running (19 kcal/min)... 

Caloric values of foods (physiological fuel values) are enthalpies of combustion but with an opposite sign, (-AH ), and corrected for energy lost in urine (e.g., as urea) and feces. While enthalpies of combustion of foods are all negative, the caloric values are given as positive numbers. Caloric values for proteins are... 

Ross, K. There is no energy in food and fuels - but they do have fuel value. School Science Review 75 (1993), 39... 

Fuel Values of Foods and Some Common Fuels... 

The bomb calorimeter described in Section 6.4 is ideally suited for measuring the energy content, or "fuel value," of foods. Fuel values are just the enthalpies of combustion (see table). In order to be analyzed in a bomb calorimeter, food must be dried first because most foods contain a considerable amount of water. Since the composition of particular foods is often not known, fuel values are expressed in terms of kj/g rather than kj/mol. 

A bomb calorimeter that may be used to measure heat released upon combustion of a sample. This device is commonly used to determine the fuel value of foods. The bomb calorimeter Is similar to the "coffee cup" calorimeter. However, note the electrical component necessary to Initiate the combustion reaction. 

Many chemical reactions that produce heat are combustion reactions. In our bodies many food substances (carbohydrates, proteins, and fats. Chapters 22 and 23) are oxidized to release energy. Fuel value is the amount of energy per gram of food. 

The fuel value of food is an important concept in nutrition science. The fuel value is generally reported in units of nutritional Calories. One nutritional Calorie is equivalent to one kilocalorie (1000 calories). It is also known as the large Calorie (uppercase C). 

A special type of calorimeter, a bomb calorimeter, is useful for the measurement of the fuel value (Calories) of foods. Such a device is illustrated in Figure 8.6. Its design is similar, in principle, to that of the "coffee cup" calorimeter discussed earlier. It incorporates the insulation from the surroundings, solution pool, reaction chamber, and thermometer. Oxygen gas is added as one of the reactants, and an electrical igniter is inserted to initiate the reaction. However, it is not open to the atmosphere. In the sealed container the reaction continues until the sample is completely oxidized. All of the heat energy released during the reaction is captured in the water. 

The amount of energy per gram of food is referred to as its fuel value. Fuel values are commonly reported in units of nutritional Calories (1 nutritional Calorie = 1 kcal). A bomb calorimeter is useful for measurement of the fuel value of foods. 

Most ctiemical reactions used for the production of heat are combustion reactions. The energy released when one gram of any substance is combusted is the fuel value of the substance. The fuel value of any food or fuel can be measured by calorimetry. 

Fuel values for some common foods are shown in T TABLE 5.4. Labels on packaged foods show the amounts of carbohydrate, fat, and protein contained in an average serving, as well as the amount of energy supplied by a serving ( FIGURE 5.24). 

TABLE 5.4 Compositions and Fuel Values of Some Common Foods ... 

Celery contains carbohydrates in the form of starch and cellulose, which have essentially the same fuel values when combusted in a bomb calorimeter. When we eat celery, however, our bodies receive fuel value from the starch only. What can we conclude about the difference between starch and cellulose as foods ... 

Estimating the Fuel Value of a Food from Its Composition... 

Analyze Here we are faced with the reverse problem, calculating the quantity of food that provides a specific fuel value. 

FOODS AND FUELS (SECTION 5.8) The fuel value of a substance is the heat released when one gram of the substance is combusted. Different types of foods have different fuel values and differing abilities to be stored in the body. The most common fuels are hydrocarbons that are found as fossil fuels, such as natural gas, petroleum, and coal. Renewable energy sources include solar energy, wind energy, biomass, and hydroelectric energy. Nuclear power does not utilize fossil fuels but does create controversial waste-disposal problems. 

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