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BASAL METABOLISM & THE ENERGY WE EXPEND
BASAL METABOLISM & THE ENERGY WE EXPEND
HOW ENERGY IS DEFINED
The gross energy in a food is the amount of heat produced by burning one gram of this foodstuff in a calorimeter.
Energy is given either in calories (a thermal heat) or in joules per gram of food.
1 calorie is the amount of heat required to raise the temperature of 1g of water by 1 degree.
A kilocalorie, called a Calorie, is equivalent to 1,000 calories.
If you convert between calories and joules (international units) you get:
1kcal = 4.185kJ
ENERGY IN FOOD
Nutrients (containing energy: carbohydrates, lipids and proteins) do not contribute all their energy to supply our bodies with the energy they need.
Some energy gets lost and this is connected with the chemical composition of foods.
What is more, some parts of certain foods cannot be digested by the small intestine or the large intestine in particular, for example about 1% of starch, 1/3 of hemicellulose fibre and 3/4 of the fibre in fruit and vegetables.
The energy that remains and which our bodies can use is called metabolisable energy; it is calculated by deducting the losses in energy in faeces and urine from the gross energy.
The amount of energy an individual expends is determined by studying the person in a calorimetric chamber over a 24 hour cycle. How much energy is expended will vary over time and is connected with several distinct processes.
This energy expenditure is measured in an individual who has been fasting for over 12 hours and who has to remain at rest, awake and in a neutral environment (as regards heat and temperature). The amount of oxygen the individual consumes is then worked out in calories per m² of their body surface area and per hour.
The energy expended allows us to work out what energy is used solely for the body's vital functions i.e. organs use energy to keep the body going even when we are asleep (heart 8%, liver 19%, muscles 20%, adipose tissue 3% etc.). We also expend energy when digesting (10%).
This then amounts to around 60% of the body's daily energy expenditure.
To calculate basal metabolism more easily, certain criteria have to be taken into account such as the person's gender, weight, height, age and their physiological and nutritional state.
Men and women:
Women have more adipose mass (fat) and this only uses up a little energy.
This means that a woman's metabolism is less than a man's (between 5 and 10% less).
How adults change as they get older:
Basal metabolic activity decreases as we grow older by about 2% to 3% per decade as the body's fat mass increases which is mostly found around the organs in the abdomen and as lean body mass decreases by about 1/3.
A simplified calculation for basal metabolism:
The equation arrived at by Black et al. is the most accurate for working out Basal Metabolism (BM):
- Women: BM = 0.963 x W0.48 x H0.50 x A-0.13
- Men: BM = 1.083 x W0.48 x H0.50 x A-0.13
W: weight in kg
H: height in meters
A: age in years
Our bodies have to deal with climatic conditions (temperatures), so maintaining our body temperature at 37 to 37.5°C is an essential function. This means that thermoregulation is both chemical (creating heat) and physical (this heat has to be transported to all the body's organs and tissues).
Carrying out any work or any outside exercise at extremely low temperatures will increase the amount of energy the body expends.
When working out energy expenditure, the second factor that has to be taken into account is how physically active we are.
This physical activity is classified according to what the activity is, how intense it is and how long it lasts.
(PAL) Physical Activity Levels are set out below in 6 categories:
PAL = 1 Sleep and siesta, resting in a reclined position
PAL = 1.5 In a sitting position: resting, TV, computer, video games,
board games, reading, writing, office work,
sewing, using transport, mealtimes...
PAL = 2.2 Standing up: getting washed and dressed, going around the house,
cooking, house work, shopping, laboratory work,
working as a sales assistant, driving machinery etc.
PAL = 3 Women: walking, gardening or equivalent, gymnastics, yoga
Men: manual work when standing up and moderately intense
(e.g. chemical industry, carpentry, etc.)
PAL = 3.5 Men: walking, gardening, work with high physical intensity
(e.g. building, plastering, car repairs etc.)
PAL = 5 Sport, intense work (e.g. excavation work, work in forests etc.)
To make things easier, the World Health Organisation's PALs are listed below based on activity over a day:
Moderate physical activity:
Intense physical activity:
Diet-induced thermogenesis (postprandial thermogenesis)
Ingesting food increases energy expenditure depending on which nutrients are eaten:
- Proteins: 20 to 30%
- Lipids: 0 to 2%
- Carbohydrates: 5 to 10%
The energy expended depends on how the food is absorbed in the intestines, processed and stored.
Energy requirements for children and adolescents
These are considerable give the body's increase in weight and size as the body produces new tissue (as the body grows and develops).
Energy requirements for pregnant and breast-feeding women
Considerable energy is required for the foetus and appendages to develop and then for milk to be produced.
How basal metabolism can vary
Basal metabolism drops when a person
- is fasting or skipping meals
- leads a sedentary lifestyle
- does not sleep -this reduces secretion of leptin which helps the body break down lipids (lipolysis)
- has hypothyroidism
- follows low calorie diets
Ways of increasing basal metabolism
- Regular physical activity increases energy expenditure by increasing our muscle mass by 5 to 10% and this increases basal metabolism.
- Having breakfast early morning stops our metabolism from slowing down after the body has been fasting through the night.
- Opting for a diet that is high in proteins, complex carbohydrates and fibre as these need more energy to be digested.
- Drinking water throughout the day helps the body perform its biochemical activities and this encourages energy expenditure.
- Stress increases basal metabolism as adrenalin is secreted.
- Running a temperature increases basal metabolism by 7% per degree
- Psychostimulants (caffeine, nicotine)
ENERGY REQUIREMENTS AND DAILY INTAKES
Daily energy expenditure (EE) determines what our energy requirements are.
They give the amount of energy that an individual needs to ingest to cover his or her requirements.
To simplify this calculation here is a way of calculating it:
EE = BM x PAL
Daily calorie intakes (excluding children, adolescents, pregnant and breast-feeding women)
Recommended daily calorie intakes are generally 130% of the average requirements for a specific population.
Reduced physical activity 8,800 kJ / 2,100 kCal
Normal activity for the majority of the population 11,300 kJ / 2,700 kCal
Considerable physical activity 12,500 kJ / 3,000 kCal
Very considerable physical activity 14,600 kJ / 3,500 kCal
Reduced physical activity 7,500 kJ / 1,800 kCal
Normal activity for the majority of the population 8,400 kJ / 2,000 kCal
Considerable physical activity 9,200 kJ / 2,200 kCal
BODY MASS INDEX (BMI)
The Body Mass Index enables us to work out how a person's build and it is calculated in the following way:
BMI = Weight / height²
(Weight in kg and Height in meters)
Here are the categories:
Under 16.5 Under-nutrition or famine
16.5 to 18.5 Thinness
18.5 to 25 Normal corpulence
25 to 30 Overweight
30 to 35 Moderate obesity
35 to 40 Severe obesity
Over 40 Morbid or massive obesity
BASAL METABOLISM IN THE DUKAN METHOD
Throughout the Dukan method diet you will increase your basal metabolism because of your protein intake and because you are physically active every day.
This means that your weight loss will be greater and more motivating during the two weight-loss phases.
What is more, by increasing your basal metabolism you will do better in the consolidation and stabilisation phases as you continue to exercise regularly.