How many Calories (that is. kilocalories) are in a 45.0 g serving of potato chips if we assume that they are essentially 50% carbohydrate and 50% fats?
Any serious effort to lose weight usually leads to studying the caloric values of foods. Have you ever wondered how the numbers quoted on food labels are obtained?
Food is "burned" In the body to yield H20, CO2, and energy, just as natural gas is burned in furnaces to yield the same products. In fact, the "caloric value" of a food is just the heat of reaction for complete combustion of the food (minus a small correction factor). The value is the same whether the food is burned In the body or In the laboratory. One gram of protein releases 4 kcal, 1 g of table sugar (a carbohydrate) releases 4 kcal, and 1 g of fat releases 9 kcal (see Table).

The caloric value of a food is usually given In 'Calories' (note the capital C), where 1 Cal = 1000 cal = 1 kcal = 4.184 kJ. To determine these values experimentally, a carefully dried and weighed food sample is placed together with oxygen In an Instrument called a calorimeter, the food Is Ignited, the temperature change Is measured, and the amount of heat given off is

Calculated from the temperature change in the calorimeter, the heat from the food is released very quickly and the temperature rise, dramatically. Clearly, though, something a bit different goes on when food is burned in the body, otherwise we would burst into flames after a meal!
It is a fundamental principle of chemistry that the total heat released or absorbed in going from reactants to products is the sane, no matter how many reactions are involved. The body ap-plies this principle by withdrawing energy from food a bit at a time in a long series of Interconnected reactions rather than all at once Si a single reaction. These and other reactions that are continually taking place in the body-called the body's metabolism-will be examined in later chapters.

Transcribed Image Text:

Caloric Values of Some Foods Substance, Sample Size Caloric Value (kcal, kJ) Protein, 1g 4, 17 Carbohydrate, 1 g 4, 17 9, 38 Fat, 1 g Alcohol, 1 g 7.1, 29.7 Cola drink, 12 fl oz (369 g) 160, 670 80, 330 5, 21 Apple, one medium (138 g) Iceberg lettuce, 1 cup shredded (55 g) White bread, 1 slice (25 g) 65, 270 Hamburger patty, 3 oz (85 g) 245, 1030 290, 1200 Pizza, 1 slice (120 g) Vanilla ice cream, 1 cup (133 g) 270, 1130 A This frosted donut provides your body with 330 Calories. Burning this donut in a calorimeter releases 330 kcal (1380 kJ) as heat.