SNAP Snippets - All things health!
This Month's Topic: BMR
Your basal metabolic rate (BMR) refers to the chemical processes going on continuously at a cellular level that allows the body to build and/or maintain its function.
It is the energy from food that is the fuel that maintains these processes (fuel). The amount of kilojoules your body burns at any given time is regulated by your metabolism.
Metabolic rate (or total energy expenditure) has 3 components
1. Basal metabolic rate (BMR) - is the amount of fuel burned at rest to maintain cellular body function and contributes 50--70 per cent of our energy needs.
2. Energy expenditure in physical work - kilojoules burned during movement and physical activity- 20 per cent of our energy needs. The more active you are the more your burn and the more muscle you have the more you burn.
3. Energy expenditure associated with eating, digesting and metabolizing food -about 5-10 per cent of our energy needs.
Contrary to popular idea - the larger a person the higher their metabolic rate. This person will also have a higher rate of energy expenditure in movement activities, such as walking and most physical work. The opposite is true for a person of light weight.
Basal (resting) metabolic rate
The BMR refers to the amount of energy the body requires to maintain itself. This accounts for 50 to 70 per cent of our total energy expenditure. Total lean mass is largely responsible for the BMR. So the more muscle the more fuel you burn simply to maintain the cellular function of the muscle. (Hence the reason crash dieting is so detrimental – it results in loss of muscle mass not necessarily loss of fat tissue)
BMR varies during the day. It is at its lowest early in the morning after 8 hours sleep and in the morning it is often10 or more hours since a person has eaten. That is why exercise in the morning is a recommendation for weight loss- is boosts BMR when it is at its lowest.
Energy expenditure in physical work
Physical exertion may burn as much as 3,000kJ per hour (see table for some examples of energy expenditure.) It is a variable component of energy expenditure- the more physical activity the more fuel that is burnt. In the resting state muscle accounts for 20 % of total expenditure this can increase remarkable during strenuous exercise (Some references quote an energy expenditure of muscle during strenuous exercise may go up to 50-fold or more.) Apart from the energy used in the exercise itself, regular physical activity affects BMR because it affects body composition.
People who are active on a regular basis have higher basal metabolic rate than non-active individuals (may be up to 10% higher for active people).Basal Metabolic Rate accounts for about two thirds of total daily energy expenditure so an increase of up to 10% is significant .
The effect of food on BMR
The basal metabolic rate rises after eating because of energy expenditure associated with eating, digesting and metabolizing food. The rise occurs soon after eating and peaks two to three hours later after a meal .The rise in BMR varies with size of the meal and the type of foods consumed. Fats have the least effect, carbohydrates have an intermediate effect and proteins cause the largest rise.
Factors affecting the BMR
The BMR on an adult is influenced by a number of factors working in combination, including:
- Body size
- Age
- Gender
- Genetic predisposition
- Amount of lean muscle tissue
- Amount of body fat
- Hormonal and nervous controls
- Dietary deficiencies
- Environmental temperature
- Infection or illness
- Fasting
- Physical activity
- Drugs
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