Energy Balance and Body Composition – Chapter 8 Study Notes

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Energy Balance

Concept of Energy Balance

Energy balance refers to the relationship between energy intake (from food and drink) and energy expenditure (through basal metabolism, physical activity, and thermogenesis). Maintaining energy balance is crucial for sustaining body weight and overall health.

Excess energy is stored as fat, which serves as a reserve for energy between meals.
Energy balance equation: (usually)
Energy imbalance leads to weight changes, which may involve changes in fat, water, lean tissue (muscle), and bone minerals.

How Much Fat is in One Pound?

Fat and Caloric Value

Understanding the caloric value of body fat is essential for weight management strategies.

1 pound of fat = 3,500 kilocalories (kcals)
To lose 1 lb of fat per week, reduce intake by 500 kcals, burn 500 kcals per day, or combine both approaches.
Rate of weight loss is influenced by sex, body composition, current weight, and weight loss history.
For long-term healthy weight loss: Lose 75% fat and only 25% lean body mass (muscle, connective tissue, bone minerals, etc.) Recommended rate: 1–2 lbs/week to maintain lean body mass.
Starvation results in protein and fat loss at a 50%–50% ratio.

Metabolic Differences Between Adipose Tissue and Muscle Tissue

Adipose vs. Muscle Tissue

Adipose and muscle tissues differ in metabolic activity and density, affecting energy expenditure and body composition.

Adipose tissue is not metabolically active.
Muscle tissue is metabolically active, even at rest; more muscle increases energy expenditure.
Lean tissue is denser than adipose tissue: Muscle: 1.06 kg/L Adipose: 0.92 kg/L

Measuring Food Energy

Direct Calorimetry

Direct calorimetry measures the energy value of food by assessing the heat released when food is burned in a bomb calorimeter.

Bomb calorimeter: Directly measures food's energy value via heat energy released.
As food is burned, chemical bonds break, and carbon and hydrogen combine with oxygen, forming heat energy, CO2, and H2O.
Kilocalorie (kcal): The amount of energy needed to raise the temperature of one kg of H2O by one degree Celsius. 1 kcal = 1,000 calories

Indirect Calorimetry

Indirect calorimetry estimates energy released by measuring the amount of oxygen consumed during food combustion.

Oxygen consumption provides an indirect measure of energy released.

kcal Calculations

Energy provided by food is calculated based on macronutrient content.

Fat: 9 kcal/g
Carbohydrate (CHO): 4 kcal/g
Protein: 4 kcal/g
Alcohol: 7 kcal/g
Tools: USDA Food Composition database, nutrition analysis software (e.g., MyFitnessPal, Cronometer, ESHA Food Processor)

Physiological Fuel Value

The physiological fuel value is the amount of energy the body actually derives from food, which may differ from calorimetry estimates due to inefficiencies in digestion and metabolism.

Calorimetry provides a reasonable estimate, not the precise amount of energy available to the body.
The body is less efficient than a calorimeter.

Appetite, Hunger, Satiation, and Satiety

Definitions and Mechanisms

Appetite, hunger, satiation, and satiety are key concepts in understanding food intake regulation.

Appetite: The prompt to eat, influenced by internal and external cues.
Hunger: Physiological response to a need for food, triggered by nerve signals and chemical messengers in the hypothalamus.
Satiation: The feeling of fullness that signals to stop eating, mediated by stomach stretch and cholecystokinin (CCK) release.
Satiety: Suppresses hunger and prevents eating for several hours after a meal.

Nutrient Composition for Sustained Satiation and Satiety

Different nutrients and food properties affect how full we feel and how long satiety lasts.

Protein is the most satiating nutrient.
Fructose stimulates appetite.
Low-energy density foods (e.g., high-fiber foods) are more satiating.
High-fat foods send strong satiety signals but are not very satiating due to high energy density in small volumes.
CCK released in response to fat in the stomach suppresses hunger and signals satiety.

Influences on Hunger, Satiation, and Satiety

Multiple factors influence hunger and satiety, including physiological, sensory, cognitive, and postabsorptive influences.

Physiological: empty stomach, gastric contractions, absence of nutrients in small intestine.
Sensory: sight, smell, taste, thought of food.
Cognitive: presence of others, social occasions, perception of hunger.
Postabsorptive: nutrients in blood, hormones, and signals from the GI tract.

The Role of the Hypothalamus

Central Regulation of Eating

The hypothalamus integrates nerve and hormonal messages related to energy intake, expenditure, and storage.

Neuropeptide Y: Causes carbohydrate cravings, initiates eating, decreases energy expenditure, and increases fat storage.
Ghrelin: Produced by the stomach, stimulates hunger.
Leptin: Produced by fat cells, increases satiety.

Categories of Energy Expenditure

Thermogenesis and Energy Use

Thermogenesis is the generation of body heat and is used to measure energy expenditure. There are three main categories:

Basal metabolism
Physical activity
Thermic effect of food

Basal Metabolic Rate (BMR)

Definition and Importance

BMR is the rate at which the body expends energy for life-sustaining activities. It reflects a fasted, awake body at rest.

Resting metabolic rate (RMR) and resting energy expenditure (REE) are related concepts.
50–65% of daily energy expenditure supports basal metabolism (e.g., breathing, heartbeat, kidney function).
Energy estimation equations provide reasonable estimates of BMR, RMR, or REE.

Factors Affecting BMR

Several factors influence BMR, as summarized in the table below.

Factor	Effect on BMR
Age	Lean body mass diminishes with age, slowing the BMR
Height	Tall, thin people have higher BMR
Growth	Children, adolescents, and pregnant women have higher BMR
Body composition & sex	More lean tissue increases BMR; more fat tissue lowers BMR
Fever	Raises BMR
Stresses	Raise BMR
Environmental temperature	Both heat and cold raise BMR
Fasting/starvation	Lowers BMR
Malnutrition	Lowers BMR
Hormones	Thyroid hormone can speed up or slow down BMR; premenstrual hormones slightly raise BMR
Smoking	Nicotine increases energy expenditure
Caffeine	Increases energy expenditure
Sleep	BMR is lowest when sleeping

Physical Activity (PA)

Role in Energy Expenditure

Physical activity involves voluntary movement of skeletal muscles and is the most variable component of energy expenditure.

Accounts for 30–50% of energy expended.
Energy expenditure depends on muscle mass, body weight, and activity (duration, frequency, intensity).

Thermic Effect of Food (TEF)

Definition and Influences

TEF is the energy expended digesting and absorbing food, typically about 10% of total energy expenditure.

Proportional to the amount of food eaten.
Greater for high-protein foods compared to fatty foods.
Greater for large meals compared to small snacks spaced out.

Additional info: TEF can be ignored in energy expenditure estimates due to its small contribution compared to other sources of error.

Adaptive Thermogenesis

Special Circumstances

Adaptive thermogenesis refers to calories burned when the body undergoes dramatic changes, such as extreme cold, overfeeding, starvation, trauma, or stress.

Involves building tissues, producing hormones and enzymes.
Not included in energy estimations for healthy adults due to variability.

Factors Included When Estimating Energy (Calorie) Needs

Key Considerations

Estimating energy needs requires consideration of several factors:

Sex: Females generally require less energy than males due to lower lean body mass.
Age: Energy needs decrease with age as lean body mass declines.
Physical activity
Body composition and size: Height and weight affect surface area; taller people have higher BMR than shorter people at the same weight.
Tools: Mifflin-St. Jeor calculator for estimating energy needs.

Body Mass Index (BMI)

Definition and Calculation

BMI is a measure of relative weight for height and is commonly used to assess body weight status.

Formula:
Example: 150 lbs and 5'8" (68") 150 lb / 2.2 = 68.2 kg 68 in x 2.54 cm/in = 172.7 cm = 1.73 m m2 kg/m2

BMI Classifications

Classification	BMI (kg/m2)
Underweight	< 18.5
Healthy weight	18.5 – 24.9
Overweight	25 – 29.9
Obese (Class I)	30 – 34.9
Obese (Class II)	35 – 39.9
Obese (Class III)	≥ 40

BMI and Mortality

BMI and mortality risk follow a U-shaped curve: risk increases as BMI declines below healthy levels or rises above them.

Pros and Cons of Using BMI

Pros: Quick personal assessment; best for population-level studies.
Cons: Does not assess body composition (overweight vs. overfat), can be stigmatizing, inaccurate for individuals, does not account for different body types or fat distribution.

Body Fat Distribution and Health Outcomes

Types of Fat Storage

Fat is distributed in two primary locations, each with different health implications.

Visceral fat: Stored around organs, contributes to central obesity, and is more common in men and post-menopausal women. Associated with increased risk of cardiovascular disease (CVD), cancers, and diabetes.
Subcutaneous fat: Stored in hips and thighs, found primarily in pre-menopausal women, and is considered cardioprotective.
Body shapes: "Apple" (android) and "pear" (gynoid) shapes reflect fat distribution patterns.

Waist Circumference and Health Risk

Waist circumference is a good measure of central adiposity and associated health risks.
Recommended limits: Females: < 35 inches (88 cm) Males: < 40 inches (102 cm)

Defining a Healthy Body Weight

Criteria and Risks

A healthy body weight supports health and longevity, with enough adipose tissue to meet basic needs but not so much as to incur health risks.

Weight alone is not an indicator of health status; metabolic and cardiovascular health are more important.

Health Risks from Low Body Fat and Underweight

Few reserves against wasting diseases
Menstrual irregularities and infertility
Osteoporosis and bone fractures

Health Risks Associated with Excess Body Fat

Body weight and fat distribution correlate with disease risk and life expectancy (not causation).
BMI between 18.5–24.9 is associated with relatively few weight-related health risks.
Other factors: smoking, substance abuse, low physical activity, stress, environment.

Metabolic Fitness and Weight

Individual Variation

Fitness levels and fat stores vary across individuals, and health risks are not solely determined by BMI.

Some overweight/obese individuals are metabolically healthy.
Some thin individuals are metabolically unfit and unhealthy.
Fat store needs vary: athletes need less, pregnant individuals and those in cold climates need more.