A problem for many people in the United States is excess body weight stored as fat. Many people have tried to capitalize on this problem with fruitless weight-loss schemes. However, since energy is conserved, an energy balance reveals only two real ways to lose weight (other than water loss): (1) reduce the caloric intake, and/or (2) increase the caloric expenditure. In answering the following questions, assume that fat contains approximately 7700 kcal/kg (1 kcal is called a “dietetic calorie” im nutrition, or commonly just a “Calorie”). (a) If a normal diet containing 2400 kcal/day is reduced by 500 kcal/day, how many days does it take lose 1 lb of fat? (b) How many miles would you have to run to lose 1 lb of fat if running at a moder- ate pace of 12 km/hr expends 400 kJ/km? (c) Suppose that two joggers each run 10 km/day. One runs at a pace of 5 km/hr and the other at 10 km/hr. Which will lose more weight (ignoring water loss)?
The Correct Answer and Explanation is :
Addressing the prevalent issue of excess body fat in the United States involves understanding the principles of energy balance, which dictate that weight loss occurs when energy expenditure exceeds caloric intake. Fat tissue contains approximately 7,700 kilocalories (kcal) per kilogram.
(a) Reducing Caloric Intake:
If an individual reduces their daily caloric intake by 500 kcal from a normal diet of 2,400 kcal/day, the daily deficit becomes 500 kcal. To lose 1 pound (approximately 0.4536 kg) of fat, which equates to a deficit of about 3,500 kcal, it would take:
[ \frac{3,500\, \text{kcal}}{500\, \text{kcal/day}} = 7\, \text{days} ]
Therefore, creating a daily deficit of 500 kcal through dietary modifications alone would result in the loss of 1 pound of fat over 7 days.
(b) Increasing Caloric Expenditure through Running:
Running at a moderate pace of 12 km/h (approximately 7.46 mph) expends about 400 kilojoules (kJ) per kilometer. To convert kilojoules to kilocalories:
[ 400\, \text{kJ/km} \times 0.239006 = 95.6024\, \text{kcal/km} ]
To lose 1 pound of fat (3,500 kcal), the distance required to run is:
[ \frac{3,500\, \text{kcal}}{95.6024\, \text{kcal/km}} \approx 36.6\, \text{km} ]
Converting kilometers to miles:
[ 36.6\, \text{km} \times 0.621371 \approx 22.8\, \text{miles} ]
Therefore, running approximately 22.8 miles at this pace would result in the loss of 1 pound of fat.
(c) Comparing Weight Loss Between Two Joggers:
Assuming both joggers run 10 km daily, we can estimate the calories burned based on their speeds. Running at different speeds affects the energy expenditure per kilometer. A general estimate is that running at 12 km/h (5 minutes per km) burns about 169 kcal for a person weighing 155 pounds (70.3 kg). citeturn0search5
For the jogger running at 5 km/h (12 minutes per km), the calorie burn is lower. Based on MET values, running at 5 km/h has a MET of approximately 6.5, while running at 12 km/h has a MET of about 12. citeturn0search22 This means the jogger running at 12 km/h would burn approximately twice as many calories per kilometer as the jogger running at 5 km/h.
Consequently, the jogger running at 12 km/h would lose more weight over the same distance due to higher energy expenditure.
Visual Representation:
To illustrate the impact of running speed on weight loss, consider the following graph:
{"image_query": "calories burned per mile running at different speeds"}
This graph demonstrates how increasing running speed enhances caloric burn per mile, thereby accelerating weight loss.
Conclusion:
Achieving weight loss requires creating an energy deficit through reduced caloric intake, increased physical activity, or a combination of both. While dietary modifications can lead to weight loss over time, incorporating higher-intensity exercises like running at faster speeds can significantly increase caloric expenditure, thereby promoting more rapid fat loss. It’s essential to tailor weight loss strategies to individual preferences and capabilities to ensure sustainability and effectiveness.