DIGESTIVE SYSTEM
Basal metabolic rate (BMR)
The BMR refers to the amount of energy your body needs to maintain homeostasis.
The basal metabolic rate (BMR) is the amount of energy that is expended at rest in a neutral
environment after the digestive system has been inactive for about 12 hours. It is the rate of
one's metabolism when waking in the morning after “fasting” during sleep.
An average man has a BMR of around 7,100 kJ per day, while an average woman has a BMR of
around 5,900 kJ per day. Energy expenditure is continuous, but the rate varies throughout the
day. The rate of energy expenditure is usually lowest in the early morning.
Factors that affect our BMR
Your BMR is influenced by multiple factors working in combination, including:
● Body size – larger adult bodies have more metabolising tissue and a
larger BMR.
● Amount of lean muscle tissue – muscle burns kilojoules rapidly.
● Amount of body fat – fat cells are ‘sluggish’ and burn far fewer kilojoules
than most other tissues and organs of the body.
● Crash dieting, starving or fasting – eating too few kilojoules encourages
the body to slow the metabolism to conserve energy. BMR can drop by
up to 15% and if lean muscle tissue is also lost, this further reduces
BMR.
● Age – metabolism slows with age due to loss of muscle tissue, but also
due to hormonal and neurological changes.
● Growth – infants and children have higher energy demands per unit of
body weight due to the energy demands of growth and the extra energy
needed to maintain their body temperature.
● Gender – generally, men have faster metabolisms because they tend to
be larger.
● Genetic predisposition – your metabolic rate may be partly decided by
your genes.
● Hormonal and nervous controls – BMR is controlled by the nervous and
hormonal systems. Hormonal imbalances can influence how quickly or
slowly the body burns kilojoules.
● Environmental temperature – if temperature is very low or very high, the
body has to work harder to maintain its normal body temperature, which
increases the BMR.
, ● Infection or illness – BMR increases because the body has to work
harder to build new tissues and to create an immune response.
● Amount of physical activity – hard-working muscles need plenty of
energy to burn. Regular exercise increases muscle mass and teaches
the body to burn kilojoules at a faster rate, even when at rest.
● Drugs – like caffeine or nicotine, can increase the BMR.
● Dietary deficiencies – for example, a diet low in iodine reduces thyroid
function and slows the metabolism.
Calorific Value
The amount of heat present in food material or fuel and which is determined
by the complete combustion of specified quantity at constant pressure and in
normal condition. It is measured in units of energy per amount of material, e.g.
kJ/kg.
The energy released by complete combustion of one gram of food is gross
calorific value.
Gross calorific value of carbohydrates - 4.1 kcal/g
Gross calorific value of proteins - 5.65 kcal/g
Gross calorific value of fats - 9.45 kcal/g
Obesity
A condition that occurs in a individual due to excessive accumulation of fat
due to a fat rich diet.In adults, obesity is often defined as having a BMI of 30
or more according to the Centers for Disease Control and Prevention (CDC).
Obesity is associated with a higher risk of developing serious diseases,
including:
● type 2 diabetes
● heart disease
● cancer
Digestive Processes
The processes of digestion include seven activities: ingestion, propulsion,
mechanical or physical digestion, chemical digestion, secretion, absorption,
and defecation.
Basal metabolic rate (BMR)
The BMR refers to the amount of energy your body needs to maintain homeostasis.
The basal metabolic rate (BMR) is the amount of energy that is expended at rest in a neutral
environment after the digestive system has been inactive for about 12 hours. It is the rate of
one's metabolism when waking in the morning after “fasting” during sleep.
An average man has a BMR of around 7,100 kJ per day, while an average woman has a BMR of
around 5,900 kJ per day. Energy expenditure is continuous, but the rate varies throughout the
day. The rate of energy expenditure is usually lowest in the early morning.
Factors that affect our BMR
Your BMR is influenced by multiple factors working in combination, including:
● Body size – larger adult bodies have more metabolising tissue and a
larger BMR.
● Amount of lean muscle tissue – muscle burns kilojoules rapidly.
● Amount of body fat – fat cells are ‘sluggish’ and burn far fewer kilojoules
than most other tissues and organs of the body.
● Crash dieting, starving or fasting – eating too few kilojoules encourages
the body to slow the metabolism to conserve energy. BMR can drop by
up to 15% and if lean muscle tissue is also lost, this further reduces
BMR.
● Age – metabolism slows with age due to loss of muscle tissue, but also
due to hormonal and neurological changes.
● Growth – infants and children have higher energy demands per unit of
body weight due to the energy demands of growth and the extra energy
needed to maintain their body temperature.
● Gender – generally, men have faster metabolisms because they tend to
be larger.
● Genetic predisposition – your metabolic rate may be partly decided by
your genes.
● Hormonal and nervous controls – BMR is controlled by the nervous and
hormonal systems. Hormonal imbalances can influence how quickly or
slowly the body burns kilojoules.
● Environmental temperature – if temperature is very low or very high, the
body has to work harder to maintain its normal body temperature, which
increases the BMR.
, ● Infection or illness – BMR increases because the body has to work
harder to build new tissues and to create an immune response.
● Amount of physical activity – hard-working muscles need plenty of
energy to burn. Regular exercise increases muscle mass and teaches
the body to burn kilojoules at a faster rate, even when at rest.
● Drugs – like caffeine or nicotine, can increase the BMR.
● Dietary deficiencies – for example, a diet low in iodine reduces thyroid
function and slows the metabolism.
Calorific Value
The amount of heat present in food material or fuel and which is determined
by the complete combustion of specified quantity at constant pressure and in
normal condition. It is measured in units of energy per amount of material, e.g.
kJ/kg.
The energy released by complete combustion of one gram of food is gross
calorific value.
Gross calorific value of carbohydrates - 4.1 kcal/g
Gross calorific value of proteins - 5.65 kcal/g
Gross calorific value of fats - 9.45 kcal/g
Obesity
A condition that occurs in a individual due to excessive accumulation of fat
due to a fat rich diet.In adults, obesity is often defined as having a BMI of 30
or more according to the Centers for Disease Control and Prevention (CDC).
Obesity is associated with a higher risk of developing serious diseases,
including:
● type 2 diabetes
● heart disease
● cancer
Digestive Processes
The processes of digestion include seven activities: ingestion, propulsion,
mechanical or physical digestion, chemical digestion, secretion, absorption,
and defecation.
