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WHAT IS METABOLISM?
It refers to all chemical reactions occurring
in the body by which one sustain the body’s vital function
as well as to the production of energy (i.e., by the breakdown of
carbohydrates and fats).
HOW DOES THE BODY PRODUCE ENERGY?
Energy is produced mainly by the breakdown of
macronutrients such as carbohydrates and fats.
ONCE “ENERGY” IS PRODUCED,
HOW IS IT DISTRIBUTTED IN THE BODY?
Total energy expenditure is comprised of 3 major
components: a) thermic effect of feeding ( TEF), b) thermic effect
of physical activity (TEPA) and c) resting metabolic rate (RMR).TEF
( i.e., it is the energy used for digesting, absorbing, and assimilating
food nutrients) accounts for about 10% of total energy expenditure
and plays a small role in total metabolism. TEPA may account
for 15 to 30 % of total caloric expenditure (i.e., physical
activity and occupational/ life style activities) and it is one
of the key factors which may affect metabolism. Finally, RMR
accounts for 60 to 80% of daily energy expenditure (i.e.,
it is the energy required at rest to maintain the body’s daily
functions) and varies greatly among individuals. Thus, the various
factors that influence RMR may include: 1) the amount of fat-free
mass, 2) amount of fat mass, 3) level of physical activity, 4) caloric
intake 5) age, 6) gender and, 7) to a minimal degree, genetics.
HOW CAN ONE INCREASE HIS/HER RMR?
RMR is greatly affected by the amount of fat-free
mass in the body. Thus, the combination of endurance and resistant
training activities will certainly affect one’s body composition.
For instance, endurance activities (i.e., running, walking, swimming)
when performed for at least 30 minutes or longer (3 to 5 x per week)
will enhance the body’s ability to utilize more fats to produce
energy. In addition, resistant training activities (i.e., weight
lifting) will enhance the body’s ability to build more muscle.
In the long run, RMR will be increased thus affecting one’s
daily total energy expenditure.
HOW DOES RMR DECREASES OR SLOW DOWN?
Since RMR is greatly affected by the amount of
fat-free mass in the body any decrease in lean tissue will affect
its metabolism. For instance, lack of physical activity will lead
to a decrease in overall muscle mass in the body, thus, decreasing
RMR. Also, individuals who are engaged in very low calorie diets
followed by rapid weight loss will signal the body to a “protection”
mode. The body will in turn, slow down its metabolism in order to
conserve energy. Lack of physical activity a decrease in total body
mass (i.e., loss of body weight), and a low caloric intake of food.
WHAT ARE THE BENEFITS
OF MEASURING ONE’S RMR?
By accurately measuring
RMR one can: a) estimate total caloric expenditure per day; b) establish
desirable goals for weigh loss or gain; c) optimize total caloric
expenditure.
HOW IS RMR MEASURED?
RMR can be estimated by:
a) predicted formulas that account for body weight and height. Although,
valid, these equations do not produce the most accurate results;
b) measuring one’s oxygen consumption (i.e.” Gold Standard
Method”, usually measured in a laboratory setting by a spirometry).
Thus, 1 liter of oxygen produces about 5 kcalories. Today, there
are portable devices that can accurately measure RMR outside the
laboratory.
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