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NST 10 Why do almost all diets fail? Dynamic nature of energy balance; what works

Why Almost All Diets Fail: The Dynamic Nature of Energy Balance

This material explores the underlying reasons why most diets fail to achieve long-term weight loss and introduces key concepts like dynamic energy balance, the role of exercise, the "fitness vs. fatness" debate, and the importance of muscle mass.

I) The Challenge of Weight Maintenance: Dynamic Energy Balance

The Misconception of Simple Energy Imbalance

  • Common Statement: Obesity is often stated as a simple state of energy imbalance (intake > expenditure).

  • Reality: This is incorrect due to the finely balanced nature of the human body's energy system.

    • Over a year, approximately 1,000,000 KCal are ingested.

    • Despite this massive intake, body weight typically remains stable within < 2 kg, equating to a balance within +/- < 10,000 KCal annually.

    • This demonstrates an incredibly precise regulatory system, not a simple linear equation.

A Thought Experiment on Energy Balance

  • Scenario 1 (Overeating): If someone ate an extra cup of ice cream (500 Kcal) every midnight for 10 years, would they gain almost a pound (3,500 Kcal) of fat per week indefinitely?

  • Scenario 2 (Undereating): If someone reduced food intake by 500 Kcal/day for 10 years, would they lose almost a pound a week indefinitely?

  • Conclusion: Of course not. This highlights that the body responds dynamically to changes in energy intake.

Adaptive Energy Expenditure (Leibel et al., 1995 Study)

  • Core Concept: The body exhibits adaptive energy expenditure (EE), meaning it burns more or fewer calories daily in response to increased or decreased energy intake.

  • Study Design: The Leibel et al. study (N Engl J Med, 1995) investigated changes in weight, body composition, and total energy expenditure (TEE) during periods of overfeeding leading to 10\% weight gain and underfeeding leading to 10\% weight loss.

  • Key Findings (Adaptive Nature of EE):

    • Weight Gain (Obese group):

      • Basal: Weight 131 kg, Total Energy Expenditure (TEE) 3160 Kcal/d.

      • 10\% gain: Weight increased to 143 kg, TEE increased to 4030 Kcal/d, resulting in a \Delta TEE of +870 Kcal/d.

    • Weight Gain (Non-obese group):

      • Basal: Weight 66 kg, TEE 2480 Kcal/d.

      • 10\% gain: Weight increased to 73 kg, TEE increased to 3110 Kcal/d, resulting in a \Delta TEE of +630 Kcal/d.

    • Weight Loss (Obese group):

      • Basal: Weight 132 kg, TEE 3100 Kcal/d.

      • 10\% loss: Weight decreased to 115 kg, TEE decreased to 2550 Kcal/d, resulting in a \Delta TEE of -550 Kcal/d.

    • Weight Loss (Non-obese group):

      • Basal: Weight 71 kg, TEE 2380 Kcal/d.

      • 10\% loss: Weight decreased to 64 kg, TEE decreased to 1950 Kcal/d, resulting in a \Delta TEE of -430 Kcal/d.

  • Conclusion: The body adapts its energy expenditure to maintain weight, making continuous weight loss or gain challenging without further caloric adjustments.

Implications of the "Dynamic Energy Balance Equation"

  • Predicting Weight Gain: Siblings with different energy expenditures gain weight differently over time in a calculable manner.

  • Diet Failure for Maintenance: While initial weight loss is often achievable, long-term maintenance is difficult.

    • It is frustrating for dieters when weight loss ceases despite consistent reduced intake.

    • Biological explanations include the body's adaptive responses.

  • Body's Defense Mechanism: The human body is programmed to defend its body weight.

    • It reduces calories burned (energy expenditure) when weight is lost and intake is reduced.

    • It also increases appetite.

    • This biological programming actively works against efforts to reach and maintain a lower weight.

    • High weight can be defended for many years, indicating that fat stores have a "long memory."

II) Role of Voluntary Exercise in Successful, Long-Term Weight Loss Maintenance

Factors for Successful Long-Term Weight Loss

  • Retrospective analysis of weight loss registries (defined as >30 pounds for >5 years) reveals two main factors:

    1. Voluntary Exercise: Approximately 3,000 Kcal/week (this is a doable amount, not necessarily marathon running).

    2. Dietary Tendency: Adherence to low energy density/low-fat diets.

Why Voluntary Activity is Crucial for Maintenance

  • The Arithmetic of Dieting: Consider an overweight person eating 2400 Kcal/day.

    • Dieting leads to a 20 pound loss, reducing intake to 1900 Kcal/d.

    • At this point, the body burns approximately 500 fewer Kcal/day than before weight loss (now burning 1900 Kcal/d to maintain new weight), leading to a cessation of weight loss.

    • This adaptation is discouraging, often leading to increased hunger and weight regain.

  • The Power of Exercise: If this person incorporates 400 Kcal/day of exercise and gains 5-10 pounds of lean muscle mass (which burns an additional 100-200 Kcal/day at rest):

    • They can continue losing weight on 1900 Kcal/d or stabilize their weight loss.

    • Even if they return to previous intake levels (2400 Kcal/d), the increased energy expenditure from exercise and muscle mass can help maintain weight.

  • Beyond Calorie Burn: Improved fitness is a significant outcome, potentially even more important than the direct calorie burn.

III) The "Fitness vs. Fatness" Question

Defining Cardiorespiratory Fitness (CRF)

  • What is Fitness?: The capacity to do aerobic work.

  • Operational Definition: Exercise capacity measured on a treadmill.

  • Conceptual Definition: The body's overall capacity to perform aerobic work.

  • Physiological Basis (Complex):

    • Oxygen Delivery: Capacity to deliver oxygen to tissues (cardiac output, blood flow to working tissues, oxygen carriage by red blood cells and hemoglobin, lung function).

    • Oxygen Consumption: Capacity of tissues to consume oxygen (mitochondrial mass and function, energy storage and mobilization, capillarization of tissues).

Is it Possible to be "Fat" and "Fit"?

  • Yes, it is possible: Examples include active Sumo wrestlers.

  • Prevalence: While possible, being overweight/obese and fit is unusual based on population data.

  • Concern for Fitness: We should care about fitness due to its strong relation to health outcomes, potentially altering the approach to obesity as a public health or medical problem.

Cardiorespiratory Fitness and Mortality (Farrell et al., 2002; Lee, Blair, & Jackson, 1999)

  • CRF at Different BMIs (Women): Data from the ACLS study (1970-1996) showed the percentage of women with moderate or high cardiorespiratory fitness across different BMI categories.

  • Relative Risk of All-Cause Mortality (Women): RRs adjusted for age, smoking, and baseline health status indicated that higher CRF categories significantly reduced the relative risk of all-cause mortality compared to the low CRF group (p < 0.002).

  • Interaction of CRF and Body Fatness (Men - Lee, Blair, & Jackson, 1999):

    • This study investigated how fitness and "fatness" impact health and survival in 21,925 men.

    • Baseline Characteristics: Data categorized men by body fatness (Lean <16.7\%\,BF; Normal 16.7\%\, to\, <25.0\%\,BF; Obese \ge 25.0\%\,BF) and fitness (Fit vs. Unfit, where Unfit was the lowest 20\% in each age group).

      • Lean Unfit men (n=327) had higher mean systolic BP (120.5 \pm 13.2 mmHg), diastolic BP (80.5 \pm 9.2 mmHg), and triglycerides (1.5 \pm 1.2 mmol/L) compared to Lean Fit men.

      • Obese Fit men (n=3217) had lower mean systolic BP (123.6 \pm 13.9 mmHg) and triglycerides (1.7 \pm 1.2 mmol/L) compared to Obese Unfit men.

    • All-Cause and CVD Mortality: The study revealed an amazing conclusion:

      • Lean unfit men have higher all-cause mortality than obese fit men.

      • Lean unfit men have higher CVD mortality than obese fit men.

      • This phenomenon is sometimes referred to as "skinny fat."

  • Implication for Public Health: The strong link between fitness and health outcomes (even outweighing fatness in some cases) suggests that fitness should be a primary focus in public health and medical approaches to obesity.

Why Might Fitness Matter?

  • Secondary Effects: Fitness can alter risk factors for disease:

    • Improved blood lipids.

    • Reduced blood pressure.

    • Enhanced insulin sensitivity and glycemia.

  • Direct Effects: Fitness may directly improve health through:

    • Better mitochondrial function.

    • Improved perfusion of organs.

  • Example: Considering the health of Sumo wrestlers while active versus after retiring illustrates the protective effects of high fitness, even in the presence of high body fat.

IV) New Biomarker: Muscle Mass

Lean Tissue (Muscle) Burns Energy

  • Determinant of Resting Energy Expenditure (REE):

    • The major determinant of REE is lean body mass (LBM).

    • Approximately half of LBM is skeletal muscle.

  • Exercise Impact: Exercise not only burns calories during activity but also, by changing body composition (increasing muscle mass relative to fat), it increases the REE.

    • This means more calories are burned even at rest.

  • REE vs. Fat Free Mass (FFM):

    • A strong positive correlation exists between FFM and REE (chart shows y = 0.09x + 1.59 with R^2 = 0.64 for REE in MJ/day vs FFM in kg).

    • However, the ratio of REE/FFM tends to decrease slightly with increasing FFM (chart shows y = -0.0006x + 0.153 with R^2 = 0.17 for REE/FFM in MJ/kg per day vs FFM in kg).

Estimation of Total Body Skeletal Muscle Mass

  • Method: Total body skeletal muscle mass can be estimated by creatine (methyl-d3) dilution in humans (Clark et al., J Appl Physiol 116: 1605-1613, 2014).