Energy in food Flashcards
How is energy released from food?
Energy is released from food by respiration, which is an oxidation process, similar in some ways to combustion. If food is combusted, it releases energy, mainly as heat.
How can we work out the energy value of any particular type of food?
We can work out the energy value of any particular type of food by assuming that respiration releases the same energy in total as combustion does.
How is the energy value found?
The energy value is found using a food calorimeter or bomb calorimeter.
How is combustion carried out?
A weighed sample of food is completely burned in an atmosphere of oxygen. The heat released by this combustion is transfered to a known volume of water, which rises in temperature as a result.
How can the energy value of food be calculated?
energy value of food in calories per gram= (temperature rise /°C * volume of water/cm3) / (mass of food sample / g)
energy value in kilojoules per gram = energy value in calories per gram * 4,2 / 1000
What are the three main energy providfing organic molecules?
The three main energy providing organic molecules found in food are fats, carbohydrates, and proteins.
Energy value of fats
39kJ per g
Energy value of proteins
20kJ per g
Energy value of carbohydrates
17kJ per g
Why do carbohydrates provide most of our energy?
Carbohydrates provide most of our energy, not because there is most energy available per gram in carbohydrates, but because we eat more grams of carbohydrates than of proteins or fats.
What is the SI unit of energy?
joule (J)
Which units is the amount of energy contained in food measured in?
The amount of energy contained in food is measured in either joules (J) or calories (cal)
1kJ
1kJ= 1000 J
1 kcal
1 kcal=1000 cal
What is a calorie?
A calorie is the amount of energy needed to raise the temperature of 1 cm3 of water by 1 C.
Calories to joules
1 calorie= 4,2 joules
What is metabolism
The total of all the chemical reactions in the body is called metabolism.
What drives metabolism?
It is driven by the enrgy from respiration, so the amount of energy needed depends on how many metabolic reactions a person is carrying out.
What are the three factors that the amount of metabolism depends upon?
BMR, activity or exercise, dynamic action of food.
BMR
The processes required to simply stay alive include breathing. excretion, thinking, and maintaining a constant temperature.
The energy consumed by these processes in one day is called basal metabolic rate.
The BMR is different for males and females, and gets less as a person gets older.
Activity or exercise
The amount of activity or exercise requires muscular work and extra temperature regulation.
Dynamic action of food
Eating food means extra work for the digestive system and the liver. The energy demand simply caused by eating is called the dynamic action of food.
energy requirement per day formula
energy requirement per day = BMR + activity + dynamic action of food.
What kind of energy does food contain?
Food contains a lot of stored chemical energy; when you eat, your body breaks down these foods into smaller components and absorbs them for fuel.
