Understanding Metabolism
Are you
aware that every day your body is constantly trying to balance energy
consumption and energy expenditure? Consumption,
or calories in, comes from the food we eat: fats, carbohydrates, proteins, and
alcohol. Expenditure, or "calories out",
refers to the amount of calories required to maintain bodily functions (resting
metabolic rate), daily physical activity, and the thermic effect of food
(Seebohar 2002). In the state of energy
balance, the amount of "calories in" is equal to the amount of "calories out"
and weight is neither gained nor lost.
Positive energy balance results in weight gain, and is when consumption
exceeds expenditure. Negative energy
balance is the opposite and results in weight loss.
Calculating
this balance is simple in theory, but is more complicated than just addition
and subtraction. It is easy to estimate the
calories that you eat and determine the ratio and quantity of fat,
carbohydrate, protein, fiber, and alcohol you consume in a given day. However, expenditure is much more complicated
and there are many factors that people over-emphasize, under-emphasize, and
don't even consider. Such overemphasized
factors include fad diets, calorie restriction (low-calorie diets), and
exercise intensity. Many individuals
underemphasize the role that weight training plays in increasing
metabolism. Also, studies show that people
overestimate their physical activity and underestimate how much they eat by 20%,
but overweight people tend to underestimate their intake by as much as 40% (Lacy
2005 2). Hopefully this will
clear up questions and myths about metabolism and help you see the bigger
picture.
A very small
contributor to burning calories is attributed to digestion and is called the
thermic effect of food (TEF). The
thermic effect is proportional to the amount of calories consumed and depends
on the amount of fat, carbohydrate, and protein in the meal. TEF is usually about 10% of the calories
consumed, so for a meal of 500 calories, 50 calories are used for
digestion. TEF is not an important
factor in weight management and should not be focused on (Seebohar 2002). Burris recommends that individuals eat every
2-3 hours to control the body's tendency to store fat (Burris, 2003).
Another topic
to consider along with nutrition is the idea of metabolic typing. Some professionals suggest that individuals
have different nutritional requirements based on their genetics. These requirements are described in types,
such as Carb Type, Protein Type, and Mixed Type. The types are much more specific than the
food guide pyramid, which does not account for individual demands (Hittner,
2004).
Expending Energy
Energy is
spent through physical activity, which consists of intentional exercise and
regular daily activity. Physical
activity provides 15-30% of your daily energy expenditure (depending on your
lifestyle), and can lead to an increase in your resting metabolic rate, which
accounts for the majority of energy expenditure in a given day. A few ways to increase physical activity
include riding a bike or walking instead of driving or taking a bus, taking the
stairs instead of the elevator, and parking in a spot far away from the
entrance to a building.
Resting
metabolic rate accounts for 60-75% of the calories individuals burn. RMR is the sum of all metabolic processes
that maintain normal body functions (Seebohar 2002). A typical RMR for males is 1500-1800 calories
a day and 1300-1600 for females. There
are many factors that influence resting metabolic rate (RMR). Body weight is the most obvious one. A person with more body weight will have a
higher RMR than a smaller one because their body needs more energy to support
and sustain the extra weight. With this
is mind, losing weight causes a decrease in RMR because there is less weight to
support and the body may be trying to conserve energy if there fewer calories
are consumed (Lacy 20051).
Potentially
the greatest influence on metabolism comes from body composition. Muscle is more metabolically active than fat,
burning 30-50 more calories than fat per pound per day. Therefore, weight gain due to an increase in
fat mass will not affect RMR as much as an increase in muscle mass (Lacy 20051). Metabolism also declines about 2-3% every 10
years, largely due to a decrease in muscle mass. This decline can be offset with the adoption
of a consistent weight training program.
One side note, there are many ways to strength train to maintain
metabolism other than the typical bodybuilding program, which is designed to
increase muscle mass and bulk.
Intensity: Cardio vs Weight Training
Regarding
exercise, metabolic rate depends on the type of exercise, duration, intensity,
and environment. More important than
mode (cardio vs weight training) is intensity.
A temporary increase in metabolism occurs immediately after exercise and
is called EPOC (excess post-exercise oxygen consumption). This EPOC is the bodies attempt to recover
from an exercise session. EPOC rises
with intensity level. However, most people
do not work out at an intensity high enough to significantly affect EPOC (Lacy
20051). An intense weight
training session can have the same effect as an intense sprint session; the
point here is that jogging for 30 minutes at 60% of your VO2 max will have
little lasting metabolic effect.
To improve
resting metabolic rate (long-term), fat-free mass must be increased. Studies have shown that training programs
designed to increase FFM have a significant effect on decreasing body fat by
increasing RMR (McCoy 2001). These are
typically strength training programs. If
you are starting a weight training program for the first time, you may see dramatic
increases in strength within the first 4-6 weeks. This is primarily due to improvements in your
intra-muscular coordination (similar to the improvements in accuracy you would
get from throwing a baseball) (Lacy, 20052). A weight training program has to be
implemented for a few months before you gain enough lean mass to change
RMR. Many studies have shown that aerobic
training has no affect on RMR (McCoy, 2001).
One particular study conducted by Wilmore, et.al in 1998 concluded that
after 20 weeks of endurance training, there was no change in RMR, even when
there were significant changes in VO2max and body composition (McCoy
2001). Aerobic training only contributes
to daily caloric expenditure, which is important for weight reduction but it
has little or no effect on RMR.
In
conclusion, there are many factors to consider when trying to balance energy
intake and expenditure. "Calories in"
can easily be estimated, but "calories out" are more obscure. We burn calories by eating food and
exercising, but mostly from our resting metabolism. Resting metabolism is affected by weight and
muscle mass; the most efficient way to improve body composition (increase the
amount of fat-free mass, decrease the amount of fat-mass) occurs through weight
training. Aerobic training is an
excellent way to decrease overall body weight and should not be neglected.
References:
Burris, Craig. "Truth in
Nutrition II." PTontheNET.
Hittner, Noah. "Metabolic
Typing." PTontheNET.
Lacy, Brigitte. "Metabolism Matters II."The
Mechanics of Metabolism." PTontheNET.
Lacy, Brigitte. "Metabolism Matters III
Myths and FAQ's." PTontheNET.
Seebohar, Bob. "The key to Weight Management:
The Energy Balance Equation and RMR." PTontheNET.
