Energy Balance and Body Composition: Study Notes for Nutrition Students

Energy Balance and Body Composition

Learning Outcomes

• Energy Balance Concepts: Define energy balance, positive energy balance, and negative energy balance as they relate to body weight.

• Components of Energy Expenditure: Explain basal metabolic rate, thermic effect of food, thermic effect of exercise, and adaptive thermogenesis.

• Measurement and Calculation: Describe methods to measure energy expenditure and calculate basal metabolic rate (BMR) and estimated energy requirements (EER).

• Body Composition: Define body composition and methods to assess lean body mass and body fat.

• Healthy Body Weight: Explain methods to estimate healthy body weight and the link between body weight and mortality.

• Eating Disorders: List criteria for diagnosing eating disorders and discuss shared traits and treatment options.

Energy Balance

Definition and Importance

Energy balance refers to the relationship between energy intake (from food and beverages) and energy expenditure (through basal metabolism, physical activity, and other processes). Maintaining energy balance is crucial for sustaining a healthy body weight.

• Positive Energy Balance: Energy intake exceeds energy expenditure, leading to weight gain. This can result from increased muscle mass, increased adipose tissue, or both. Common during periods of growth such as pregnancy, childhood, and adolescence.

• Negative Energy Balance: Energy expenditure exceeds energy intake, resulting in weight loss. This may involve loss of fat, muscle, glycogen, or water.

Concept of Energy Balance

Energy balance is achieved when energy intake equals energy expenditure. Imbalances lead to changes in body weight.

Energy Intake

• Bomb Calorimeter: Measures kilocalories in foods and beverages. Results are adjusted for physiological fuel values, which reflect the actual energy transformed in the body.

• Physiological Fuel Values:

  • Carbohydrate and protein: 4 kcal/gram

  • Fat: 9 kcal/gram

  • Alcohol: 7 kcal/gram

Energy Expenditure

• Basal Metabolism: Energy required for basic physiological functions.

• Thermic Effect of Food (TEF): Energy used to digest, absorb, and metabolize food (about 10% of energy intake).

• Thermic Effect of Exercise (TEE): Energy expended during physical activity.

• Adaptive Thermogenesis: Energy used in response to environmental changes (e.g., stress, temperature, diet).

Components of Total Daily Energy Expenditure (TDEE)

Total Daily Energy Expenditure (TDEE) is the total kilocalories needed to meet daily energy requirements. It consists of:

• Basal Metabolic Rate (BMR): 50–70%

• Thermic Effect of Exercise (TEE, includes NEAT and adaptive thermogenesis): 20–35%

• Thermic Effect of Food (TEF): 10%

Basal and Resting Metabolic Rate

Definition and Influencing Factors

Basal Metabolic Rate (BMR) is the amount of energy spent to meet the body's basic physiological needs. Resting Metabolic Rate (RMR) is often used as a practical estimate.

• Factors Influencing BMR:

  • Lean body mass

  • Age

  • Gender

  • Body size

  • Genes

  • Ethnicity

  • Emotional and physical stress

  • Thyroid hormone levels

  • Nutritional state

  • Environmental temperature

  • Caffeine and nicotine

Table: Factors That Affect Basal Metabolism

Factor	Explanation
Lean body mass	Higher muscle mass increases BMR.
Age	BMR declines with age.
Gender	Men typically have higher BMR due to more muscle mass.
Body size	Larger individuals have higher BMR.
Genes	Genetic factors can influence BMR.
Race	Ethnic differences may affect BMR.
Hormones	Thyroid hormones increase BMR.
Starvation	Prolonged fasting lowers BMR.
Environmental temperature	Extreme temperatures can increase BMR.
Caffeine/Drugs	Stimulants increase BMR.

Physical Activity and Thermogenesis

Thermic Effect of Exercise (TEE) and NEAT

• TEE: Energy expended during physical activity; varies by activity type, duration, and body weight.

• Non-Exercise Activity Thermogenesis (NEAT): Energy expended from daily activities not considered exercise.

Thermic Effect of Food (TEF)

• TEF: Energy used to process macronutrients and extract kilocalories from food.

  • Protein-rich meals have higher TEF than carbohydrate-rich meals, which have higher TEF than fat-rich meals.

  • Influenced by nutrient type, meal composition, alcohol intake, age, and training status.

Adaptive Thermogenesis

• Regulation of heat production in response to environmental changes (stress, temperature, diet).

• May explain differences in body composition among individuals with similar diets and activity levels.

Measuring Energy Expenditure

Calorimetry Methods

• Direct Calorimetry: Measures energy expenditure by assessing body heat loss in a metabolic chamber.

• Indirect Calorimetry: Estimates energy expenditure by measuring oxygen consumption and carbon dioxide production.

Estimating Energy Requirements

• Simple calculations use age, gender, height, weight, and physical activity level.

• Estimated Energy Requirement (EER): Calculated using predictive equations.

• Resting Metabolic Rate (RMR): Often estimated using the Harris-Benedict equation:

Harris-Benedict Equation:

• Men: $BMR = 88.362 + (13.397 imes ext{weight in kg}) + (4.799 imes ext{height in cm}) - (5.677 imes ext{age in years})$

• Women: $BMR = 447.593 + (9.247 imes ext{weight in kg}) + (3.098 imes ext{height in cm}) - (4.330 imes ext{age in years})$

Multiply BMR by an activity factor to estimate TDEE.

Body Composition

Definition and Importance

Body composition is the ratio of fat tissue to lean body mass (muscle, bone, organs), usually expressed as percent body fat. It is important for assessing health risks associated with excess body fat.

Types of Body Fat

• Essential Fat: Required for normal body function. Women: ~12%, Men: ~3%.

• Stored Fat:

  • Subcutaneous fat: Located under the skin.

  • Visceral fat: Stored around abdominal organs; insulates and protects organs.

• Brown Adipose Tissue (BAT): Specialized fat cells with many mitochondria; generate heat.

Body Fat Distribution

• Central (Android) Obesity: Excess visceral fat in the abdomen; increases risk for heart disease, diabetes, hypertension.

• Gynoid Obesity: Excess fat around thighs and buttocks; more common in women.

Table: Body Composition Reference Standards

	Men	Women
Essential fat	3% of total body fat	12% of total body fat
Desirable fatness for good health	10–20% body fat	16–26% body fat
Overfat	More than 25% body fat	More than 30% body fat

Assessing Body Composition

Indirect Methods

• Hydrostatic Weighing: Underwater weighing; highly accurate (2–3% error).

• Air Displacement Plethysmography (BodPod): Measures air displacement; accurate within 3%.

• Dual-Energy X-ray Absorptiometry (DEXA): Most accurate; 1–4% error; measures bone density and body mass.

• Bioelectrical Impedance Analysis (BIA): Measures resistance to electrical current; less accurate than density tests.

• Skinfold Caliper: Measures fat at various body sites; accuracy depends on technician skill.

• Waist Circumference: Quick indicator of health risk; increased risk if >35 inches (women) or >40 inches (men).

Estimating Healthy Body Weight

Methods

• Height and Weight Tables: Provide recommended weight ranges based on height, gender, and frame size; limited accuracy.

• Body Mass Index (BMI): Calculates body weight in relation to height; useful for screening disease risk.

BMI Formula: $BMI = rac{ ext{weight (kg)}}{ ext{height (m)}^2}$

Health Risks Associated with Body Weight and Composition

Underweight

• Increased risk of malnutrition, anemia, osteoporosis, heart irregularities, amenorrhea, depression, anxiety, infection, and premature death.

Overweight and Obesity

• Increased risk of heart disease, hypertension, stroke, gallstones, hyperlipidemia, sleep apnea, reproductive problems, and certain cancers.

• More than 80% of people with type 2 diabetes are overweight.

• Central obesity is associated with metabolic syndrome.

Disordered Eating and Eating Disorders

Definitions and Types

• Disordered Eating: Abnormal and potentially harmful eating patterns (e.g., refusing to eat, binge eating, purging, abusing diet pills).

• Eating Disorders: Psychological illnesses diagnosed by specific criteria; most common in young adults and adolescents.

Table: Diagnostic Criteria for Eating Disorders (inferred summary)

Disorder	Key Criteria
Anorexia Nervosa	Self-starvation, excessive weight loss, fear of gaining weight, restrictive eating, excessive exercise
Bulimia Nervosa	Binge eating followed by purging, use of laxatives, vomiting, or excessive exercise
Binge Eating Disorder	Recurrent episodes of binge eating without purging
Orthorexia	Obsession with healthy eating, elimination of foods based on perceived health risks
Night Eating Syndrome	Consuming most daily calories after evening meal, waking to eat at night

Health Consequences

• Anorexia Nervosa: Electrolyte imbalances, low heart rate, fatigue, hair loss, digestive slowing, nutrient deficiencies, inability to regulate body temperature.

• Bulimia Nervosa: Tears in esophagus, tooth decay, gum disease, electrolyte imbalances, dehydration, constipation, impaired bowel function.

• Binge Eating Disorder: High blood pressure, high cholesterol, heart disease, type 2 diabetes, gallbladder disease.

Treatment Approaches

• Multidisciplinary team: psychological, medical, and nutrition professionals.

• Registered Dietitian Nutritionist: meal planning, food journals, identifying triggers, recognizing hunger/fullness cues.

• Early intervention increases likelihood of full recovery.

Example

A young adult with central obesity (android pattern) may have increased risk for cardiovascular disease and metabolic syndrome due to excess visceral fat. Assessment using waist circumference and BMI can help determine health risk and guide interventions.

Additional info: Equations and reference standards are provided for practical application in clinical and academic settings.