Effects of Physical Activity on Obesity

Lecture Objectives

• Summarize components that determine total daily energy expenditure (TDEE).

• Discuss the effects of dietary restriction on TDEE components.

• Examine how dietary restriction affects body composition.

• Understand the effects of combined dietary restriction and physical activity on TDEE components.

• Explore how combined dietary restriction and physical activity affect body composition.

Introduction

• The lecture seeks to engage students in thinking beyond prior knowledge about calories and energy balance in relation to obesity.

Key Facts

1. Energy Content in Fat

   • One pound of fat contains approximately $3,500$ kcals (kilocalories).

   • The term "kcals" is the accurate scientific term, but it is synonymous with the familiar term "calories" used in everyday contexts (e.g., $180$ calories in a soda).

2. Daily Caloric Expenditure

   • Average daily caloric expenditure for individuals generally ranges from $2,000$ to $2,500$ calories.

   • This implies that a pound of fat, when oxidized, can fuel the body for nearly $2$ days.

3. Caloric Expenditure per Mile

   • Walking or jogging a mile burns between $100$ to $125$ calories.

   • The same caloric expenditure applies to both walking and jogging despite differences in intensity, as caloric burn over a distance is similar regardless of speed.

Energy Storage vs. Energy Expenditure

• Historically, during hunter-gatherer periods, the conservation of fat (energy store) was advantageous in times of scarcity.

• The current relationship between the energy stored in fat and expenditure through physical activity is more problematic due to the abundance of high-calorie foods and sedentary lifestyles.

Weight Change Equation

• The formula for weight change is:

  • $\text{Weight Change} = ext{Energy Intake} - ext{Energy Expenditure}$

  • If energy intake exceeds expenditure, weight increases.

  • If energy expenditure exceeds intake, weight decreases.

Example Calculation

• Consider an individual weighing $150$ pounds with $15\%$ body fat:

  • Total body fat = $150 \times 0.15 = 22.5$ pounds

  • Total calories stored = $22.5 \times 3,500 = 78,750$ calories (approx. $80,000$ calories).

  • If they burn $2,000$ calories/day, it would take them approximately $40$ days to oxidize all fat without any caloric intake.

Energy Expenditure Components

1. Resting Metabolic Rate (RMR)

   • Accounts for $60-75\%$ of total daily energy expenditure (up to about $1,500$ calories).

   • Functions continuously to maintain vital bodily processes, dependent on muscle mass.

   • Examples: A muscular person burns more calories at rest than a less muscular individual.

2. Thermic Effect of Food (TEF)

   • Accounts for approximately $10\%$ of total calorie intake (e.g., consuming $2,000$ calories results in about $200$ calories lost due to digestion and metabolism).

3. Energy Expenditure from Physical Activity

   • Accounts for about $15-30\%$ of total daily energy expenditure; varies widely based on physical activity levels and body mass.

Reduction in Caloric Intake and Its Effects

• When individuals restrict calories, several outcomes may occur:

  • RMR decreases, as the body adapts to potential starvation.

  • TEF decreases since fewer calories are consumed.

  • For sustained physical activity, if body mass decreases, energy expenditure during activity also declines.

Effects of Diet and Physical Activity on Energy Expenditure

• Including exercise with dietary reduction does not compensate for decreased caloric expenditure due to dieting, as shown in various studies:

  • Numerous studies (historically involving cohorts of approximately $25$ female participants per group) indicated similar reductions in RMR between dieting alone and dieting with exercise.

Relationship Between Diet and Exercise on Body Composition

• Studies indicate that weight loss through dieting often results in both fat and lean mass loss, with concerns regarding the preservation of muscle mass:

  • Activities focused on resistance training may mitigate lean mass loss compared to aerobic exercises alone.

Successful Weight Loss Strategies and Results

• The National Weight Control Registry demonstrates successful weight maintenance strategies:

  • The registry tracks over $10,000$ participants to identify trends in sustainable weight loss.

  • The demographic distribution is approximately $80\%$ female and $20\%$ male.

  • Successful weight loss requires a combination of reduced caloric intake and increased energy expenditure through physical activity.

  • Regular physical activities, particularly walking, contributed significantly to maintaining weight loss.

Conclusion

• In summary, energy balance is influenced greatly by the interplay between dietary intake and physical activity.

• Understanding the components of energy expenditure is critical for addressing obesity and successful weight management.

References

• Note relevant literature and research findings mentioned throughout the lecture.

• Consider the historical context of physical activity's role in human survival and its application to contemporary issues of obesity.