EXAMPLE 4–14 Burning Off Lunch Calories
A 90-kg man had two hamburgers, a regular serving of french fries, and a
200-ml Coke for lunch (Fig. 4–43). Determine how long it will take for him
to burn the lunch calories off (a) by watching TV and (b) by fast swimming.
What would your answers be for a 45-kg man?
Solution A man had lunch at a restaurant. The times it will take for him to
burn the lunch calories by watching TV and by fast swimming are to be
determined.
Assumptions The values in Tables 4–1 and 4–2 are applicable for food and
exercise.
Analysis (a) We take the human body as our systemand treat it as a closed
systemwhose energy content remains unchanged during the process. Then
the conservation of energy principle requires that the energy input into the
body must be equal to the energy output. The net energy input in this case
is the metabolizable energy content of the food eaten. It is determined from
Table 4–1 to be
The rate of energy output for a 68-kg man watching TV is given in Table 4–2
to be 72 Calories/h. For a 90-kg man it becomes
Therefore, it will take
to burn the lunch calories off by watching TV.
(b) It can be shown in a similar manner that it takes only 47 minto burn the
lunch calories off by fast swimming.
Discussion The 45-kg man is half as large as the 90-kg man. Therefore,
expending the same amount of energy takes twice as long in each case:
18.6 hby watching TV and 94 minby fast swimming.
EXAMPLE 4–15 Losing Weight by Switching to Fat-Free Chips
The fake fat olestra passes through the body undigested, and thus adds zero
calorie to the diet. Although foods cooked with olestra taste pretty good, they
may cause abdominal discomfort and the long-term effects are unknown. A
1-oz (28.3-g) serving of regular potato chips has 10 g of fat and 150 Calo-
ries, whereas 1 oz of the so-called fat-free chips fried in olestra has only 75
Calories. Consider a person who eats 1 oz of regular potato chips every day at
lunch without gaining or losing any weight. Determine how much weight this
person will lose in one year if he or she switches to fat-free chips (Fig. 4–44).
¢t887 Cal
95.3 Cal>h9.3 hEout 1 90 kg 2 ¬72 Cal>h
68 kg95.3 Cal>h887 Cal 2 275 250 87Ein 2 Ehamburger EfriesEcolaChapter 4 | 199FIGURE 4 –43
A typical lunch discussed in
Example 4 –14.
© Vol. 30/PhotoDiscFIGURE 4 –44
Schematic for Example 4 –15.