exam 3 energy balance

Energy Balance and Body Composition

Learning Objectives

This section outlines the foundational concepts in energy balance and body composition, which are essential for understanding nutrition and its impact on health.

• Energy balance and its consequences

• Physical, emotional, and environmental influences on food intake

• Components of energy expenditure and influencing factors

• Distinction between body weight and body composition; assessment methods

• Relationships between body weight and chronic diseases

Energy Balance

Biochemical Reactions in the Body

Energy balance refers to the relationship between energy intake (calories consumed) and energy expenditure (calories used by the body). Maintaining energy balance is crucial for healthy body weight and metabolic function.

• Energy stored as fat is used for energy between meals.

• Energy balance equation: $\text{Energy in} = \text{Energy out}$

• Imbalance causes weight changes, but not simply fat changes.

• 3500 kcal rule: Traditionally, 1 pound of fat is considered equivalent to 3500 kcal, but this is not exactly correct and varies by sex and weight.

Example: If a person consumes more calories than they expend, the excess is stored as fat, leading to weight gain.

Measuring Food Energy

Bomb Calorimeter and Physiological Fuel Value

Food energy is measured to understand how much energy is available for the body’s metabolic processes. The bomb calorimeter is a device used to determine the energy value of foods.

• Bomb calorimeter: Measures food’s energy value by combusting food and recording temperature changes in water.

• Physiological fuel value: The actual amount of energy the body derives from food, which may differ from the calorimeter value due to digestion and absorption efficiency.

• Direct measure: Energy released is measured by oxygen consumed and heat produced.

• Calorie calculations: Used to estimate energy intake and expenditure.

Example: A food sample is placed in a bomb calorimeter; the heat released raises the temperature of water, which is measured to calculate the energy content.

Components of Energy Expenditure

Overview of Energy Expenditure

Energy expenditure is the total amount of energy used by the body, which includes several components.

• Basal Metabolism: Energy required for basic physiological functions at rest (e.g., breathing, circulation).

• Physical Activity: Energy used during movement and exercise; most variable component.

• Thermic Effect of Food (TEF): Energy needed to digest, absorb, and metabolize food; accounts for ~10% of energy intake.

• Adaptive Thermogenesis: Energy expended in response to dramatic changes (e.g., illness, injury).

Equation:

$\text{Total Energy Expenditure (TEE)} = \text{Basal Metabolic Rate (BMR)} + \text{Physical Activity} + \text{Thermic Effect of Food (TEF)} + \text{Adaptive Thermogenesis}$

Factors Influencing Food Intake

Physical, Emotional, and Environmental Influences

Food intake is regulated by a complex interplay of physiological, psychological, and environmental factors.

• Physical cues: Hunger and satiety signals from the body

• Emotional influences: Stress, mood, and psychological state can affect eating behavior

• Environmental cues: Time of day, food availability, sight, and taste of food

Example: People may eat more when food is readily available or when experiencing emotional stress.

Body Weight vs. Body Composition

Definitions and Assessment Methods

Body weight is a measure of total mass, while body composition refers to the proportion of fat, muscle, bone, and other tissues.

• Body weight: Total mass of an individual

• Body composition: Percentage of fat, muscle, bone, and other tissues

• Assessment methods: Skinfold thickness, bioelectrical impedance, dual-energy X-ray absorptiometry (DEXA), underwater weighing

Example: Two individuals may have the same body weight but different body compositions; one may have more muscle, the other more fat.

Body Weight and Chronic Disease

Relationships and Risks

Body weight and composition are closely linked to the risk of developing chronic diseases.

• Overweight and obesity: Increase risk for cardiovascular disease, diabetes, certain cancers, and other health problems

• Underweight: Associated with increased risk of osteoporosis, infertility, and weakened immune function

• Fat distribution: Visceral fat (around organs) is more strongly linked to disease risk than subcutaneous fat (under the skin)

Example: Excess visceral fat increases the risk of metabolic syndrome and type 2 diabetes.

Key Equations and Tables

Body Mass Index (BMI)

BMI is a widely used screening tool for assessing healthy body weight.

• Equation:

$\text{BMI} = \frac{\text{weight (lb)} \times 703}{\text{height (in)}^2}$

Classification Table:

BMI Range	Classification	Health Risk
< 18.5	Underweight	Increased risk of mortality, osteoporosis
18.5 - 24.9	Normal weight	Lowest risk
25 - 29.9	Overweight	Increased risk of chronic diseases
≥ 30	Obese	High risk of premature death and chronic diseases

Methods for Measuring Body Fat

Method	Description
Skinfold Thickness	Measures subcutaneous fat using calipers
Bioelectrical Impedance	Estimates body composition by electrical conductivity
DEXA	Dual-energy X-ray absorptiometry; measures bone density and body fat
Underwater Weighing	Assesses body density by water displacement

Summary

Understanding energy balance and body composition is fundamental for nutrition students. These concepts are critical for evaluating dietary needs, assessing health risks, and developing effective nutrition interventions.