Under 7MNT0004 Sources of Energy (Week 2)

Sources of Energy

Overview

Presented by: Dr. Yemisi Latunde-Dada
Department: Nutritional Sciences, School of Life Course & Population Sciences, Faculty of Life Sciences & Medicine

Energy Sources and Expenditure

Discussion regarding various energy sources and how they are expended.

Learning Objectives

Units of Energy: Describe the units of energy that are used for measuring food energy content.
Sources of Energy: Define the main sources of energy in the UK diet.
Measurement of Gross Energy: Explain how gross energy content of foods may be measured.
Atwater Factors: Apply Atwater factors to calculate energy contents of foods with known macronutrient composition.
Energy Density Factors: Recognise the main factors influencing the energy density of foods.

Main Concepts

Units of Energy
Sources of Energy
Determination of Energy Contents of Foods
Gross Energy vs. Metabolizable Energy
Atwater Factors
Energy Density of Foods

What is Energy?

Definition and types of energy:
- Solar
- Thermal
- Mechanical
- Chemical
- Electrical

First Law of Thermodynamics

Principle: Energy cannot be created or destroyed; it can only be converted from one form to another.
- Examples of Energy Conversion:
- Car engine: Chemical → Mechanical
- Battery: Chemical → Electrical
- Photosynthesis: Solar → Chemical
- Food: Chemical → Heat; Mechanical energy.

Uses of Energy in the Body

Energy is required for:
- Growth, pregnancy, lactation, and repair.
- Body functioning (keeping warm, breathing, pumping blood).
- Physical activity (movement of muscles).

Measurement of Energy in Food

Units of Measurement:
- Kilocalories (kcal) and the SI unit, kilojoules (kJ).
- Definitions:
- 1 Joule: Energy used when 1 kg is moved 1 m by a force of 1 Newton.
- 1 Calorie: Amount of heat needed to raise the temperature of 1 g of water from 15.5 to 16.5 °C.
- Conversion: 1 kcal = 4.184 kJ.
- Example: 1 slice of bread is 70 kcal or 293 kJ.

Calculating Energy Content

Questions for practice:
- A packet of crisps is 175 kcal. How many kJ?
- If 1 sausage roll contains 285 kJ, how many calories if 3 are consumed?

Answers to Practice Calculations

Packet of Crisps: 175 kcal = 732 kJ.
Sausage Roll Consumption: 3 sausage rolls = 273 kcal.

Sources of Energy in the Diet

Macronutrients contributing to energy:
- Carbohydrate > Fat > Protein
- Also includes alcohol.
Statistical Data from NDNS (2008-2012):
- Average daily intake:
- 8.88 MJ/day (2111 kcal/day)
- 6.78 MJ/day (1613 kcal/day)

Carbohydrates

◼ Simple or complex (sugar, starch, fibre)
❑ MONOSACCHARIDES – glucose, fructose, galactose
❑ DISACCHARIDES – sucrose, lactose, maltose
❑ POLYSACCHARIDES – starch and non-starch
polysaccharides (fibre)
◼ Stored in liver and muscle as glycogen – limited
supply of readily available energy
◼ Good sources – cereals, beans, tubers, fruits,
honey, syrup

Fats

Definition: Triglycerides (triacylglycerol) comprised of 3 fatty acids attached to a glycerol backbone.
Functions:
- Energy storage (unlimited), insulation, organ protection, and cell membrane formation.
Good sources:
- Meat, oils, dairy products.

Proteins

Definition: Nitrogen-containing macromolecules consisting of amino acids.
Functions:
- Structural components of muscles, connective tissues, skin, enzymes (growth and maintenance).
Essential Amino Acids:
- Eight essential out of twenty total amino acids.
Good sources:
- Meat, dairy, beans, pulses.

Energy Content Measurement Method

Utilize Bomb Calorimeter:
- Oxygen at high pressure ignites food, leading to oxidation.
- Measure released energy as heat in a surrounding water jacket.
Gross Energy (GE): Total energy of food when fully oxidised.

How do we know the energy content of

food?

By oxidising (burning) it using a bomb calorimeter

▪ Use oxygen at high pressure and an

electric element to ignite the food and

oxidise it to give water, CO2 and

nitrogen oxides.

▪ The released energy is measured as

a heat rise in a water jacket surrounding

the combustion chamber.

▪ Total energy of foodstuff = Gross

energy (GE) (heat given off when fully

oxidised in bomb calorimeter).

Metabolizable Energy (See table on slides)

Metabolizable Energy (ME) calculated from:
$ME = GE - (Energy ext{ in faeces} + Energy ext{ in urine})$
Method of measurement:
- Perform bomb calorimetry on food, faeces, and urine over a 7-day intake.
Atwater Factors: Developed by Wilbur Olin Atwater (1844-1907) for estimating energy from known macronutrient content.

Atwater Factors

Presentation of data for energy release per gram:
- Carbohydrates: 4 kcal/g (17 kJ/g).
- Protein: 4 kcal/g (17 kJ/g), with a loss of 1.8 kcal/g in urine.
- Fats: 9 kcal/g (37 kJ/g).
- Alcohol: 7 kcal/g (29 kJ/g).

Differences in Carbohydrate Energy Release

Variability in hydrolysis of carbohydrates affects energy yield:
- Example: 100 g of sucrose yields 105 g of glucose and fructose.
Assessment measures:
- Carbohydrates can be expressed as monosaccharide equivalents.

Complex Version of Atwater’s System

Adjusted values for food types according to:
- Heat of combustion, food processing, and fiber content.
Reference from FAO Food and Nutrition paper 77 for detailed methods.

Differentiating Atwater Factors

General Atwater Factor: Standard estimates based on average absorption.
Specific Atwater Factor: Tailored estimates based on specific food contents.

UK and USA Food Composition Tables

UK Reference: McCance and Widdowson.
USA Reference: USDA National Nutrient Database.
- Established by Atwater and Woods, includes data for over 130 nutrients across 7000 foods.

Estimating Energy Content of Foods

Methods:
- Bomb Calorimetry.
- Food recall and diaries: 24-hour and food frequency questionnaires.
- Novel Methods such as Automatic Ingestion Monitor (AIM).

Variability in Food Energy Content

Example Comparisons:
- A sedentary female expends 2000 kcal (8368 kJ) per day requiring:
- 13 kg of green peppers.
- 0.38 kg of milk chocolate.
- 1.5 kg of boiled white rice.

Energy Density of Foods

Definition: Amount of energy (calories) per gram of food; relates to the energy stored per unit of mass (kJ/g).
Determinant: Water content.
- Example moments: Raw rice (11% water) = 3.8 kcal/g vs. Boiled rice (70% water) = 1.4 kcal/g.
- Inverse Relationship: Foods with higher water content typically have lower energy density, and vice versa.

Factors Influencing Energy Density and Choices

Foods with high energy density (e.g., walnuts, butter) have different macronutrient compositions compared to low energy density foods (fruits and vegetables).
Promoting Satiety with Low-Energy-Dense Foods (LEDF):
- Incorporating LEDF helps control hunger and can aid weight management.

Sample Menus and Energy Analysis

Comparison of high and low energy density menu:
- High energy density menu averages 2584 kcal over various meals.
- Low energy density menu totals 1686 kcal over many meals, supporting healthier choices.

Importance of Energy Sources

Comparison between diets containing alcohol versus non-alcohol diets.
- Identify potential dietary risks related to high fat intake and cardiovascular disease (CVD).

Practical Exercise

Tasks include calculating energy value, weight percentages of macronutrients, and its significance in diet formulation and analysis.

Summary of Key Points

Food energy measured in calories or joules, derived from carbohydrates, fats, proteins, and alcohol.
Carbohydrates stored as glycogen, fats as triglycerides with limitless storage, proteins as amino acids.
Methods to measure energy include bomb calorimetry and Atwater factors for estimating metabolizable energy

Exercises Related to National Diet and Nutrition Survey

Identify contributions of cereals, meat, milk, and eggs to UK diet energy intake.
Examine ways to decrease dietary energy density for health benefits.

Thank You

Presented by: Dr. Yemisi Latunde-Dada