Lecture #23

Question 1

What are the two main components of energy balance?

Answer 1

Energy intake and energy expenditure

Question 2

How does the First Law of Thermodynamics apply to the human body?

Answer 2

According to the First Law of Thermodynamics, energy can be neither created nor destroyed, only transformed.

The human body adheres to this principle by transforming energy from food into heat through the oxidation process, with heat serving as a measure of energy utilization.

Question 3

What is a Calorie, and how is it defined in terms of energy?

Answer 3

A Calorie (with a capital “C”) refers to a kilocalorie (kcal), or 1,000 calories.

It is the amount of energy needed to raise the temperature of 1kg of water from 15 to 16 degrees Celsius. In dietary terms, 1 food Calorie is equivalent to 1 kcal.

Question 4

What is metabolizable energy, and why is it significant?

Answer 4

The difference between the gross energy of consumed food and the energy contained in feces and urine (both measured by bomb calorimetry)

It highlights that not all ingested nutrients are metabolized for energy, and the human body cannot extract all calories from the combustion of food due to differences in macronutrients’ chemical compositions and caloric density.

Question 5

What are Atwater General Factors, and how are they determined?

Answer 5

The Atwater General Factors are values used to estimate the energy content of macronutrients in food.

They were determined by comparing the energy measured in a bomb calorimeter with the energy found in feces and urine, thereby calculating the energy retained in excretory products. This process established the coefficient of availability for different macronutrients.

Question 6

How does dietary fibre affect the metabolizable energy content of food?

Answer 6

Dietary fibre affects the metabolizable energy content by:

1. Reducing transit time in the intestine, thus lessening digestion and absorption time.
2. Increasing stool bulk and water-holding capacity, which slows diffusion of digested products to the intestinal mucosa for absorption.
3. Potentially causing mechanical erosion of the mucosal surface, leading to increased excretion of endogenous materials alongside undigested/non-absorbed nutrients.
4. Allowing for the liberation of energy through the fermentation of fiber.

Question 7

What happens if the intake of metabolizable energy is insufficient to sustain metabolic processes?

Answer 7

If the intake of metabolizable energy is insufficient, the body mobilizes its energy stores:

1.Triglycerides (TG) from white adipose tissue (WAT)

2. Glycogen from the liver and skeletal muscles

The balance of energy in and out ultimately determines the size of the body’s fat and glycogen compartments.

Question 8

What are the primary determinants of energy expenditure in the body?

Answer 8

1. Basal Metabolic Rate (BMR)
2. The Thermic Effect of Food (TEF) or Diet-Induced Thermogenesis (DIT)
3. Adaptive Thermogenesis (regulation of body temperature)
4. Physical Activity