Sources Of Energy

What is energy?

Energy is a quantatitive property that can be transferred and transformed. It is the ability to do work done

What is energy used for?

-Body functioning- to keep warm ,breathe ,pump blood round the body

-Growth, pregnancy, lactation and repair

-To move around- to power the muscles

How is the energy in food measured?

Kilocalories (kcal) or the SI unit, kilojoules (kJ)

1 joule

energy used when 1kg is moved by 1m by a force of 1 newton

1kcal

4.184kJ

1 calorie

the amount of heat needed to raise temperature of 1g water from 15.5 to 16.5 or the amount of heat liberated on the total combustion of 1g of pure benzoic acid

Sources of energy in the diet

From macronutrients

• Carbohydrates

• Fats

• Proteins

• Alcohol

Monosaccharides

Glucose,fructose,galactose

Disaccharides

Sucrose,lactose,maltose

Polysaccharides

starch and non-starch polysaccharides (fibre)

Where are carbohydrates stored?

Stored in the liver and muscle as glycogen-limited supply of readily available energy

Good sources of carbohydrates

Cereals,beans,tubers,fruits,honey and syrup

Triglycerides (triacyglycerol)

3 fatty acids on glycerol backbone

Function of fats

• Energy storage (unlimited)

• Insulation

• Organ protection

• Cell membranes

Good sources of fats

meats,oils,dairy

What are proteins made up from?

Nitrogen-containing macromolecules made of amino acids

Functions of Proteins

• Structural componennet of muscle,connective tissue,skin etc,enzymes,growth and maintenance

How many essential amino acids are there?

8 essential amino acids. 20 in total

Good sources of protein

meat,dairy,beans and pulses

How do we know the energy content of food?

By oxidising (burning) it using a bomb calorimeter

Bomb calorimetry method

• Use oxygen at high pressure and an electric element to ignite the food and oxidise it to give water, carbon dioxide 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- heat given off when fully oxidised in bomb calorimeter

Metabolizable Energy (ME) =

Gross energy - energy in faces and urine

How to determine the ME

Intake over 7 days, you would have to perform bomb calorimetry on food,faeces and urine

Atwater Factors

ME content of protein, fat and CHO estimated separately so a whole food could be predicted

Why does food produce less energy when metabolized than when burnt?

This is because of the loss in faeces (undigested) and in urine (urea)

1g of CHO when metabolized

Produces 3.75 kcal (16kJ)

1g of protein when metabolized

4kcal (17kJ)

1g of fat when metabolized

Produces 9kcal (37kJ)

1g of alcohol produces

7kcal (29kJ)

Are carbohydrates 4 or 3.75 kcal?

The same weight of carbohydrates yields different amounts of monosaccharides upon hydrolysis and thus different amounts of energy

Atwater’s complex system

This specific system derives different values for proteins, fats and CHOs depending on which food they are in, the heat of combustion of proteins which can vary,food processing and fibre content

Estimation of Energy Content of Foods

• Bomb calorimetry

• Food recall and food diaries- 24h, food frequency questionnaire

• Novel methods for Assessing Food and Energy Intake

• -The Automatic Ingestion Monitor

• Intelligent Food-Intake Monitor

• GoCARB

Energy density

the amount of energy per gram of food. Energy stored per unit of volume (kj/ml) or mass

What foods have low energy density?

Fruits and veg typically have high water content (80-95%), high dietary fibre content and low in fat. The additon of them to a meal can lower overall energy content as their bulk reduces consumption of starch/fatty foods

Dietary fat

9kcal/g is the main determinant of dry energy density

Relationship between water content and energy density

As the water content increases, energy density decreases

How many catergories of energy density can be divided?

4

Very low ED (energy density)

<0.6kcal/g, free foods to eat any time, e.g almost all fruit and non-strachy vegetables and broth based soups

Low ED

0.6-1.5kcal/g, eat reasonable portions, e.g wholegrains, lean proteins, legumes and low-fat dairy

Medium ED

1.6-3.9kcal/g, manage your portions e.g breads,desserts,fat-free baked snacks,cheeses and higher fat metas

High ED

4-9kcal/g, carefully manage portions and frequency of eating, e.g Fried snacks, candy ,cookies, nuts and fats

How can low energy dense foods help?

It can promote satiety and help control hunger. A pattern can meet energy and nutrient needs to avoifd weight gain or lose excess weight. Has wide applicability and can be a key component of a lifestyle choice that encourages a well balanced diet for healthy weight

Does it matter where we get energy from?

Energy sources has been associated with disease risk factors e.g high fat diets and CVD)

Metabolisable Energy

Can be calculated using Atwater factors