Week 4 - energy requirements

Question 1

what is gross energy, digestiable energy and metabolisable energy?

Answer 1

• Gross energy (GE) : total chemical energy contained within. Food determined by complete oxidation in a bomb calorimeter
• Digestable energy (DE): the proportion of GE that is actually absorbed across the digestive tract
• Metabolizable energy (ME): The amount the energy in foods available for human metabolism. Allows for loss in the urine due to incomplete combustion in the body

Question 2

what is a atwater factor?

Answer 2

• From studied by Atwater, he derived the “Atwater factors”

* Atwater factors” reflect metabolisable energy per gram of macronutrient

Question 3

what are the atwater factors of protein, carbohydrates, fibre, fat and alcohol?

Answer 3

• Protein: 17KJ/gram
• Fat: 37KJ/gram
• Carbohydrates: 17KJ/gram
• Alcohol: 29KJ/gram
• Fibre: 8KJ/gram

Question 4

what is meant by the energy density of food?

Answer 4

Energy density of a food is the density of a whole food which is usually a mixture of macronutrients, water and other components

• Related to how much water is in a food
• Oil: 37KJ/g
• Celery: 0.2KJ/g
• Oil Is much more energy dense as there is 0 water and TF pure fat
• Celery has majority water -> therefore very low in energy density