Download LESSON 3.2 WORKBOOK What is fast and slow metabolism?

LESSON 3.2 WORKBOOK
What is fast and slow metabolism?
In the last lesson we saw data showing that the
extent of obesity in the United States has risen
dramatically, and we evaluated how obesity is
measured. In this lesson we will explore how exercise and body composition relate to metabolic
rates. The concepts we will cover include the
idea that ‘fast’ and ‘slow’ metabolism is largely a
consequence of lean muscle mass. We will also
explore other factors that may contribute to metabolic rate, such as efficiency of food absorption.
Our metabolism determines our caloric needs
In Unit 2 we learned a lot about metabolism. Metabolism is the process of breaking down macronutrients
to release energy, which in turn is used by every cell in the body. How does this process of metabolism
relate to how much we should eat and the idea of fast and slow metabolism?
Are you stuck with the metabolism you were born with?
Can you alter your metabolism? If you want to gain or lose weight, slowing or speeding up your metabolism seems like a good way to do it. Although there are some factors that you may be able to change
about your metabolism, like muscle mass and your diet, others like your age, you are stuck with!
Wo r k b o o k
Lesson 3.2
________________________________
________________________________
________________________________
________________________________
________________________________
________________________________
________________________________
________________________________
________________________________
________________________________
________________________________
________________________________
________________________________
________________________________
________________________________
________________________________
________________________________
________________________________
________________________________
________________________________
________________________________
________________________________
________________________________
________________________________
________________________________
________________________________
________________________________
________________________________
________________________________
________________________________
________________________________
________________________________
________________________________
________________________________
________________________________
________________________________
115
LESSON READINGS
1. Which of the following is NOT
associated with a fast metabolism?
aa. Muscle mass.
bb. Younger age.
cc. Hyperthyroidism.
dd. Iodine deficiency.
Muscle mass can influence your metabolic rate
DEFINITIONS OF TERMS
Thyroid — A large gland in
the neck that secretes thyroid
hormone.
For a complete list of defined
terms, see the Glossary.
Wo r k b o o k
Lesson 3.2
A person that can eat a lot of food and never gain weight may
be enviously labeled as having a 'fast metabolism', but are there
biological reasons that explain this phenomenon? It is true that
some people burn through calories quicker than others, but this
effect is not so much based on luck, but rather based on the body
composition of each individual. We have previously introduced the
concept that muscle tissue is more metabolically active than fat
tissue. Therefore, a person with more muscle mass will need more
calories to maintain that tissue than a person that weighs the same
but is made up mostly of fat tissue. In fact, just maintaining 5 pounds
of lean muscle is estimated to costs about 100-250 calories per day!
Figure 1: Muscles use
more calories to maintain
than fat.
The thyroid controls metabolic rate
The thyroid is a gland located in your neck that produces thyroid hormone from amino acids and iodine.
One of the main roles of the thyroid is to regulate metabolism by making thyroid hormone and sending
it throughout the body. Thyroid hormone passes into cells where they change the expression of genes
that are involved in metabolism of carbohydrates, lipids and proteins. By changing the amount of thyroid
hormone in a cell, the rate that carbohydrates, lipids and proteins are metabolized is also changed. Thyroid disorders
can speed up or slow down metabolism,
depending on whether the thyroid is
making too much or too little thyroid
hormone. People with hyperthyroidism
have too much thyroid hormone, and
may feel sensitive to heat, be hyperactive
and generally have a faster metabolism.
People with hypothyroidism do not make
enough thyroid hormone and are often
cold, have little appetite, are sluggish
Figure 2: The thyroid is a butterfly shaped gland
and have a slower metabolism. Having
located in your neck. Thyroid hormone is an imporeither an under or overactive thyroid can
tant regulator of metabolic rate.
alter body composition because of these
changes in metabolism.
________________________________
________________________________
________________________________
________________________________
________________________________
________________________________
________________________________
________________________________
________________________________
________________________________
________________________________
________________________________
________________________________
________________________________
________________________________
________________________________
________________________________
________________________________
________________________________
________________________________
________________________________
________________________________
________________________________
________________________________
________________________________
________________________________
________________________________
________________________________
116
LESSON READINGS
2. Which of the following can reduce
metabolic rate?
aa. Increasing muscle mass.
bb. Hyperthroidism.
cc. Eating too few calories.
dd. Eating too many calories.
Thyroid disorders are relatively common in the U.S. (about 5-8% of the
population is affected), and are more likely to affect older adults and
women. If someone is diagnosed with a thyroid disorder they can receive
medication to correct thyroid hormone concentrations. Because iodine
is necessary for the production of thyroid hormone, iodine deficiency
results in hypothyroidism. To reduce cases of hypothyroidism due to iodine
deficiency, most salt in the United States is fortified with iodine.
Low calorie and low carbohydrate diets slow down metabolism
Figure 3:
Iodine is added
to salt to prevent
thyroid problems.
It is true that if you consume fewer calories in a day than you burn, you will
eventually lose weight. Unfortunately, the simple equation of energy input
equaling energy output isn’t always true. When a very low calorie diet is
consumed, and not enough calories are supplied to fuel cellular processes
and physical activity, metabolism actually slows down. A drop in caloric intake below 1000 calories a day
can lead to a reduction in metabolic rate by 50%! The body will adapt by increasing metabolic efficiency,
so each cell will use less calories to perform its normal functions. Non-essential cellular functions will
cease, and a feeling of extreme fatigue will set in. Additionally, eating a calorie restricted diet may hinder
the muscle’s ability to grow, so if you are eating few calories but still exercising your muscles will not be
able to repair themselves and grow, leading to a further reduction in muscle mass. As we know, your
muscle mass affects your metabolic rate, so a decrease in muscle mass will also reduce the 'speed' of
metabolism.
Wo r k b o o k
Lesson 3.2
Figure 4: Cutting carbohydrates completely
from the diet may reduce your muscle’s ability to
grow.
Similarly, a diet that is restrictive in
carbohydrate intake will rely on digesting
proteins from muscles for glucose. Recall
that the liver performs gluconeogenesis
using amino acids to make new glucose
to export to the blood for the brain and
red blood cells. Without carbohydrate
consumption gluconeogenesis is the only
source of glucose, and amino acids from
the muscle and the diet will be processed
into glucose. If a person is consuming a
carbohydrate-free diet and still exercising
regularly, amino acids may be shuttled
away from the muscles and to the liver
instead, reducing the person’s ability to
build new muscle tissue.
________________________________
________________________________
________________________________
________________________________
________________________________
________________________________
________________________________
________________________________
________________________________
________________________________
________________________________
________________________________
________________________________
________________________________
________________________________
________________________________
________________________________
________________________________
________________________________
________________________________
________________________________
________________________________
________________________________
________________________________
________________________________
________________________________
________________________________
________________________________
117
LESSON READINGS
Some things you just can’t change
DEFINITIONS OF TERMS
Basal metabolic rate — The
rate that the body uses energy
while at rest to keep vital functions going, such as breathing
and keeping warm.
Energy expenditure — The
total amount of energy used by
a body; can by calculated by
adding up basal metabolic rate,
energy used for physical activity
and the thermic effect of food.
For a complete list of defined
terms, see the Glossary.
Figure 5: Resistance
training, like weight lifting, can help maintain
muscle mass as we age.
As we age our metabolic rate tends to decrease. Children will burn
through calories much faster than older adults. This is in part because
organs (like the heart, liver, brain and kidneys) make up a larger proportion of a child’s body weight than an adult, and organ tissue accounts
for large portion of the calories burned. Moreover, children’s bodies are
growing rapidly, and calories must be used to grow their tissues and
organs. Metabolism drops substantially after puberty is completed, and
then slowly declines throughout the rest of life largely because of a loss
of lean muscle mass. While we cannot stop ourselves from aging, we
can reduce its impact by participating in resistance training, which builds
muscle, and eating more protein rich foods, which helps us maintain
muscle mass.
There is some evidence that you may have inherited your metabolic from your parents. Studies in twins
have demonstrated that people with identical genetics have similar metabolic rates, however the contribution of genetics to metabolism hasn’t been completely sorted out. It seems that your genetics may play
a role in determining your metabolism, but your metabolic rate is not set in stone, and can be altered by
exercise and diet.
How is energy from metabolism used?
We have now learned that once energy is
released from food it is used for physical activity
and biological processes. We will now break
down energy expenditure into three categories: basal metabolic rate, thermic effect of food,
and physical activity.
Basal metabolic rate uses the most calories
Wo r k b o o k
Lesson 3.2
Basal metabolic rate represent the minimal
amount of energy used in a fasting state to
keep a resting, awake body alive in a warm,
quiet environment. For a sedentary person,
basal metabolism accounts for about 60-70%
Figure 6: Energy expenditure can be
divided into three categories: basal metabolic
rate (60-70% of energy expenditure, physical
activity (25-40%) and the thermic effect of
food (5-10%).
3. Physical activity can increase energy
expenditure by:
aa. Burning more calories.
bb. Increasing muscle mass.
cc. Reducing muscle loss.
dd. All of the above.
________________________________
________________________________
________________________________
________________________________
________________________________
________________________________
________________________________
________________________________
________________________________
________________________________
________________________________
________________________________
________________________________
________________________________
________________________________
________________________________
________________________________
________________________________
________________________________
________________________________
________________________________
________________________________
________________________________
________________________________
________________________________
________________________________
________________________________
________________________________
118
LESSON READINGS
of energy expenditure. Some of the processes involved include the beating of the heart, respiration of
the lungs, and activity of the liver, brain and kidneys. The building up and breaking down of your muscles
also uses energy that contributes to the basal metabolic rate. We can’t change the size or metabolic rate
of most organs in our body, but we can increase the size (and therefore the metabolic rate) of the muscle
tissue.
Amount of calories used for physical activity depends on you!
DEFINITIONS OF TERMS
Physical activity — Movement
that we consider exercise, including resistance training, sports and
dancing.
Physical activity increases energy expenditure above and beyond basal energy needs by as much
as 25-40%. By choosing to be active or inactive we can change how much energy we expend in a day.
Unfortunately, energy expenditure from physical activity varies widely among people, so it’s not possible
to give a formula for how much activity is needed to increase energy expenditure by a certain number
of calories. Physical activity may have the most effect on energy expenditure by changing our body
composition (increasing muscle mass), in turn changing the basal metabolic rate.
Thermic effect of food — Energy used to digest, absorb and
metabolize the food that we eat.
For a complete list of defined
terms, see the Glossary.
Figure 7: People that
fidget burn calories through
NEAT: non-exercise activity
thermogenesis.
Another type of energy expenditure due to exercise is called
NEAT, which stands for non-exercise activity thermogenesis.
NEAT is the energy that is used for everything that is not
sleeping, eating or what we consider exercise. This means
that walking to school or the grocery store, cooking a meal,
gardening, fidgeting, and basically any movement you do that
is not intended to be exercise is considered NEAT. Because
NEAT encompasses most of our movement a person that
does a lot of exercise but has a low NEAT level may still be at
risk for becoming overweight of obese. On the flip side, people
that tend to fidget more, or get their exercise by walking to work
or taking stairs instead of elevators may be able to stave of
weight gain over time.
Energy is used to digest food
Wo r k b o o k
Lesson 3.2
In addition to BMR and physical activity, the body uses energy to digest, absorb and metabolize the food
that we eat. This is called the thermic effect of food, and is like a sales tax. We’re charged 5-10% of the
total energy that we eat to cover the cost of processing the food. For every 100 calories consumed, 5-10
of those calories are used to simply process the food. In addition, food composition influences how many
calories are lost to the thermic effect. For example, a protein rich meal has a higher thermal effect than a
carbohydrate or fat rich meal, because it takes more energy to metabolize amino acids than glucose or
fatty acids. In addition, large meals result in a higher thermal effect of food than the same amount of food
eaten over many hours.
4. Going to soccer practice would
be considered _____, while using
energy to sit up straight all day is
considered _____.
aa. Physical activity; basal metabolic
rate.
bb. Exercise; physical activity.
cc. NEAT; basal metabolic rate.
dd. Physical activity; NEAT.
5. Energy used to break down
nutrients free from a fibrous food is
considered?
aa. NEAT.
bb. The thermic effect of food.
cc. Basal metabolic rate.
dd. All of the above.
________________________________
________________________________
________________________________
________________________________
________________________________
________________________________
________________________________
________________________________
________________________________
________________________________
________________________________
________________________________
________________________________
________________________________
________________________________
________________________________
________________________________
________________________________
119
STUDENT RESPONSES
Mary is a 68-year-old woman who feels her metabolism has 'slowed'. What would you tell Mary about the possible causes of
this change? How can she speed up her metabolism?
_____________________________________________________________________________________________________
_____________________________________________________________________________________________________
_____________________________________________________________________________________________________
_____________________________________________________________________________________________________
_____________________________________________________________________________________________________
_____________________________________________________________________________________________________
____________________________________________________________________________________________________
Remember to identify your
sources
_____________________________________________________________________________________________________
_____________________________________________________________________________________________________
_____________________________________________________________________________________________________
_____________________________________________________________________________________________________
_____________________________________________________________________________________________________
_____________________________________________________________________________________________________
_____________________________________________________________________________________________________
_____________________________________________________________________________________________________
_____________________________________________________________________________________________________
_____________________________________________________________________________________________________
_____________________________________________________________________________________________________
_____________________________________________________________________________________________________
_____________________________________________________________________________________________________
_____________________________________________________________________________________________________
_____________________________________________________________________________________________________
_____________________________________________________________________________________________________
Wo r k b o o k
Lesson 3.2
_____________________________________________________________________________________________________
___________________________________________________________________________________________
120
TERMS
TERM
For a complete list of defined
terms, see the Glossary.
Wo r k b o o k
Lesson 3.2
DEFINITION
Basal Metabolic Rate
The rate that the body uses energy while at rest to keep vital functions going, such as breathing and keeping
warm.
Energy Expenditure
The total amount of energy used by a body; can by calculated by adding up basal metabolic rate, energy
used for physical activity and the thermic effect of food.
Physical Activity
Movement that we consider exercise, including resistance training, sports and dancing.
Thermic Effect of Food
Energy used to digest, absorb and metabolize the food that we eat.
Thyroid
A large gland in the neck that secretes thyroid hormone.
121