METABOLISM: encompasses all chemical changes occurring in living organisms.

What is a metabolic pathway? It describes a series of chemical reactions where something is either broken down from a large compound into smaller units, this action is called catabolism or when there is a building up of more complex molecules from smaller ones which is called anabolism.

The resting metabolic rate (RMR) is energy that is expended when the body is at rest; it refers to the minimum amount of energy necessary to sustain life and bodily functions. Energy is measure in kilojoules in South African, where the abbreviation is kJ and in other countries in the world it is measure in calories (cal). The conversion rate is 1 cal is equal to 4.186 kJ (or rounded to 4.2kJ).

The factors that affect the metabolic rate are:

• Lean Body Mass Influences

– Age
– Gender
– degree of muscle development
– body size

• Aging

– Lean BM decreases while body fatness rises, resulting in an RMR reduction of about 2 to 3 percent per decade
– A way to combat this would be to engage in some physical activity during the aging process.

• Certain Medications

– Chemotherapy, HGH, Thyroid meds

• Thyroid Function

• Other

– Altitude
– Exercise
– Environmental Temperature
– Caffeine Intake

• Smoking

The thermic effect of food refers to the energy that is expended as a result of the digestion and processing of food for storage and use. The amount of energy that this usually takes is between 6 – 10% of total energy expenditure during the day.

Exercise and energy expenditure differs depending on the amount of physical activity that has been undertaken. The more exercise being done, increases the body’s energy requirements. Physical activity can account for around 20% of total energy requirements by an individual.

Estimating total energy

TER (Total Energy Requirements) RMR (resting metabolic rate) + TEF (thermic effect of food) + PA (physical activity)

RMR = weight (kg) x 10
TEF = 10% of RMR
PA = RMR x PA Factor (see below)

PHYSICAL ACTIVITY CHART (Adults 19 years and older)
Very lightSeated and standing activities, office work, driving, nothing vigorous1.2 – 1.3
Low ActiveIn addition to the activities of “very light”, 30 minutes of moderate activity.  Refers to most office works with 30 minutes of planned exercise.1.5 – 1.6
ActiveThis now includes 3 hours of physical activity.1.6 – 1.7
StrenuousThis includes planned vigorous training, physical labour or full time athletes.1.9 – 2.1

Adapted from the Food and Nutrition Board, Dietary Reference Intakes for Energy, Carbohydrates, Fat, Protein, and Amino Acids (macronutrients).  Washington DC: National Academy of Sciences, 2002.