Body Mass Index (BMI) is widely and routinely used by healthcare professionals as an indicator of body fatness. BMI is a quick, inexpensive tool that can be useful to get a general idea of a person’s disease risk, however, it isn’t perfect. Using your textbook and the resources below, discuss the advantages and disadvantages of BMI. Are there any limitations to using BMI to assess a person’s health? If you were a healthcare professional, what advice would you give to clients about interpreting their own BMI? Do you think BMI more important than healthy behaviors?
https://www.cdc.gov/obesity/downloads/bmiforpactit…
https://www.rachaelhartleynutrition.com/blog/probl…
CHAPTER 8. ENERGY
Chapter 8. Energy | 453
Introduction
Hoʻā ke ahi, kōʻala ke ola
Light the fire for there is life-giving substance
Image
by G.E.
Ulrich, USGS
/ CC BY-SA
2.0
Learning Objectives
By the end of this chapter, you will be able to:
•
Describe the body’s use, storage and balance of
energy
•
Describe factors that contribute to weight
Introduction | 455
management
•
Identify evidence-based nutritional
recommendations
Months and months of training lead up to one of the most
prestigious one-man (or woman) outrigger canoe paddling races in
the world, the Ka‘iwi Channel Solo World Championship. Athletes
from Hawai‘i and across the world paddle from the island of Molokai
to Oahu in the Ka‘iwi Channel, whose name carries the meanings
of its two core words “the bones.” The channel is said to be one of
the most treacherous bodies of water and depending on the ocean
conditions top paddlers finish between 3 1/2 and 6 hours. Paddlers
spend hours and hours each week training to physically prepare
their bodies and minds for the race but equally important is the
refueling that takes place off the water. Each paddler will say they
have their own “secret” training nutrition plan which may consist of
a specific food or drink they prefer, but the bottom line is that the
energy from carbohydrates, protein, and fat they ingest is required
to fuel their body for training, recovering and repairing so they are
able to continue to perform at high levels. Having a nutrition plan
for race day is equally important for achieving peak performance
and there are all sorts of products available with claims about
digestibility,
energy-sustenance,
and
promises
of
optimal
performance results. Even with all of these highly specified and
formulated products many paddlers prefer to rely on what fueled
Native Hawaiians and other ancient voyager, poi. Poi, made of
watered down pa‘i‘ai or mashed kalo (taro) was considered a
voyaging staple and for many paddlers it continues to be. This easily
transported food contains water that supports hydration, energyrich carbohydrates, and for some serves as a connection to their
voyaging ancestors, making it a “go-to” for many paddlers as they
cross the Ka‘iwi Channel.
456 | Introduction
Energy is essential to life. Normal function of the human body
requires a constant input and output of energy to maintain life.
Various chemical components of food provide the input of energy to
the body. The chemical breakdown of those chemicals provides the
energy needed to carry out thousands of body functions that allow
the body to perform daily functions and tasks such as breathing,
walking up a flight of steps, and studying for a test.
Energy is classified as either potential or kinetic. Potential energy
is stored energy, or energy waiting to happen. Kinetic energy is
energy in motion. To illustrate this, think of an Olympic swimmer
standing at the pool’s edge awaiting the sound of the whistle to
begin the race. While he waits for the signal, he has potential
energy. When the whistle sounds and he dives into the pool and
begins to swim, his energy is kinetic (in motion).
In food and in components of the human body, potential energy
resides in the chemical bonds of specific molecules such as
carbohydrates, fats, proteins, and alcohol. This potential energy is
converted into kinetic energy in the body that drives many body
functions ranging from muscle and nerve function to driving the
synthesis of body protein for growth. After potential energy is
released to provide kinetic energy, it ultimately becomes thermal
energy or heat. You can notice this when you exercise and your
body heats up.
The Calorie Is a Unit of Energy
The amount of energy in nutrients or the amount of energy
expended by the body can be quantified with a variety of units
used to measure energy. In the US, the kilocalorie (kcal) is most
commonly used and is often just referred to as a calorie. Strictly
speaking, a kcal is 1000 calories. In nutrition, the term calories
almost always refers to kcals. Sometimes the kcal is indicated by
capitalizing calories as “Calories.” A kilocalorie is the amount of
Introduction | 457
energy in the form of heat that is required to heat one kilogram of
water one degree Celsius.
Most other countries use the kilojoule (kJ) as their standard unit
of energy. The Joule is a measure of energy based on work
accomplished – the energy needed to produce a specific amount of
force. Since calories and Joules are both measures of energy, one
can be converted to the other – 1 kcal = 4.18 kJ.
Estimating Caloric Content
The energy contained in energy-yielding nutrients differs because
the energy-yielding nutrients are composed of different types of
chemical bonds. The carbohydrate or protein in a food yields
approximately 4 kilocalories per gram, whereas the triglycerides
that compose the fat in a food yield 9 kilocalories per gram. A
kilocalorie of energy performs one thousand times more work than
a calorie. On the Nutrition Facts panel found on packaged food, the
calories listed for a particular food are actually kilocalories.
Estimating the number of calories in commercially prepared food
is fairly easy since the total number of calories in a serving of a
particular food is listed on the Nutrition Facts panel. If you wanted
to know the number of calories in the breakfast you consumed
this morning just add up the number of calories in each food. For
example, if you ate one serving of yogurt that contained 150 calories,
on which you sprinkled half of a cup of low-fat granola cereal that
contained 209 calories, and drank a glass of orange juice that
contained 100 calories, the total number of calories you consumed
at breakfast is 150 + 209 + 100 = 459 calories. If you do not have
a Nutrition Facts panel for a certain food, such as a half cup of
blueberries, and want to find out the amount of calories it contains,
go to Food-a-pedia, a website maintained by the USDA. For more
details on food composition data, go to the USDA Food Composition
Databases page.
458 | Introduction
An Organism Requires Energy and Nutrient
Input
Energy is required in order to build molecules into larger
macromolecules (like proteins), and to turn macromolecules into
organelles and cells, which then turn into tissues, organs, and organ
systems, and finally into an organism. Proper nutrition provides
the necessary nutrients to make the energy that supports life’s
processes. Your body builds new macromolecules from the
nutrients in food.
Nutrient and Energy Flow
Energy is stored in a nutrient’s chemical bonds. Energy comes from
sunlight, which plants capture and, via photosynthesis, use it to
transform carbon dioxide in the air into the molecule glucose. When
the glucose bonds are broken, energy is released. Bacteria, plants,
and animals (including humans) harvest the energy in glucose via a
biological process called cellular respiration. In this process oxygen
is required and the chemical energy of glucose is gradually released
in a series of chemical reactions. Some of this energy is trapped
in the molecule adenosine triphosphate (ATP) and some is lost as
heat. ATP can be used when needed to drive chemical reactions in
cells that require an input of energy. Cellular respiration requires
oxygen (aerobic) and it is provided as a byproduct of photosynthesis.
The byproducts of cellular respiration are carbon dioxide (CO2)
and water, which plants use to conduct photosynthesis again. Thus,
carbon is constantly cycling between plants and animals.
Introduction | 459
Figure 8.1
Energy Flow
From Sun to
Plants to
Animals
Plants harvest energy from the sun and capture it in the molecule
glucose. Humans harvest the energy in glucose and capture it into
the molecule ATP.
Food Quality
One measurement of food quality is the amount of nutrients it
contains relative to the amount of energy it provides. High-quality
foods are nutrient dense, meaning they contain lots of nutrients
relative to the amount of calories they provide. Nutrient-dense
foods are the opposite of “empty-calorie” foods such as carbonated
sugary soft drinks, which provide many calories and very little, if
any, other nutrients. Food quality is additionally associated with
its taste, texture, appearance, microbial content, and how much
consumers like it.
460 | Introduction
Learning Activities
Technology Note: The second edition of the Human
Nutrition Open Educational Resource (OER) textbook
features interactive learning activities. These activities are
available in the web-based textbook and not available in the
downloadable versions (EPUB, Digital PDF, Print_PDF, or
Open Document).
Learning activities may be used across various mobile
devices, however, for the best user experience it is strongly
recommended that users complete these activities using a
desktop or laptop computer.
An interactive H5P element has been excluded
from this version of the text. You can view it
online here:
humannutrition2e22/?p=282#h5p-81
Introduction | 461
The Atom
Cells are the basic building blocks of life, but atoms are the basic
building blocks of all matter, living and nonliving. The structural
elements of an atom are protons (positively charged), neutrons (no
charge), and electrons (negatively charged). Protons and neutrons
are contained in the dense nucleus of the atom; the nucleus thus has
a positive charge. Because opposites attract, electrons are attracted
to this nucleus and move around it in the electron cloud.
Electrons contain energy, and this energy is stored within the
charge and movement of electrons and the bonds atoms make with
one another. However, this energy is not always stable, depending
on the number of electrons within an atom. Atoms are more stable
when their electrons orbit in pairs. An atom with an odd number
of electrons must have an unpaired electron. In most cases, these
unpaired electrons are used to create chemical bonds. A chemical
bond is the attractive force between atoms and contains potential
energy. By bonding, electrons find pairs and chemicals become part
of a molecule.
Bond formation and bond breaking are chemical reactions that
involve the movement of electrons between atoms. These chemical
reactions occur continuously in the body. We previously reviewed
how glucose breaks down into water and carbon dioxide as part of
cellular respiration. The energy released by breaking those bonds
is used to form molecules of adenosine triphosphate (ATP). Recall
how during this process electrons are extracted from glucose in a
stepwise manner and transferred to other molecules. Occasionally
electrons “escape” and, instead of completing the cellular
respiration cycle, are transferred to an oxygen molecule. Oxygen (a
molecule with two atoms) with one unpaired electron is known as
superoxide (Figure 8.2).
Atoms and molecules such as superoxide that have unpaired
electrons are called free radicals; those containing oxygen are more
462 | The Atom
specifically referred to as reactive oxygen species. The unpaired
electron in free radicals destabilizes them, making them highly
reactive. Other reactive oxygen species include hydrogen peroxide
and the hydroxyl radical.
Figure 8.2
Superoxide
Image by
DoSiDo / CC
BY-SA 3.0
A molecule with one unpaired electron, which makes it a free
radical.
The reactivity of free radicals is what poses a threat to
macromolecules such as DNA, RNA, proteins, and fatty acids. Free
radicals can cause chain reactions that ultimately damage cells.
For example, a superoxide molecule may react with a fatty acid
and steal one of its electrons. The fatty acid then becomes a free
radical that can react with another fatty acid nearby. As this chain
reaction continues, the permeability and fluidity of cell membranes
changes, proteins in cell membranes experience decreased activity,
and receptor proteins undergo changes in structure that either
alter or stop their function. If receptor proteins designed to react
to insulin levels undergo a structural change it can negatively affect
glucose uptake. Free radical reactions can continue unchecked
unless stopped by a defense mechanism.
The Atom | 463
Metabolism Overview
Metabolism is defined as the sum of all chemical reactions required
to support cellular function and hence the life of an organism.
Metabolism is either categorized as catabolism, referring to all
metabolic processes involved in molecule breakdown, or anabolism,
which includes all metabolic processes involved in building bigger
molecules. Generally, catabolic processes release energy and
anabolic processes consume energy. The overall goals of
metabolism are energy transfer and matter transport. Energy is
transformed from food macronutrients into cellular energy, which
is used to perform cellular work. Metabolism transforms the matter
of macronutrients into substances a cell can use to grow and
reproduce and also into waste products. For example, enzymes are
proteins and their job is to catalyze chemical reactions. Catalyze
means to speed-up a chemical reaction and reduce the energy
required to complete the chemical reaction, without the catalyst
being used up in the reaction. Without enzymes, chemical reactions
would not happen at a fast enough rate and would use up too
much energy for life to exist. A metabolic pathway is a series of
enzyme catalyzed reactions that transform the starting material
(known as a substrate) into intermediates, that are the substrates
for subsequent enzymatic reactions in the pathway, until, finally,
an end product is synthesized by the last enzymatic reaction in
the pathway. Some metabolic pathways are complex and involve
many enzymatic reactions, and others involve only a few chemical
reactions.
To ensure cellular efficiency, the metabolic pathways involved in
catabolism and anabolism are regulated in concert by energy status,
hormones, and substrate and end-product levels. The concerted
regulation of metabolic pathways prevents cells from inefficiently
building a molecule when it is already available. Just as it would be
inefficient to build a wall at the same time as it is being broken
464 | The Atom
down, it is not metabolically efficient for a cell to synthesize fatty
acids and break them down at the same time.
Catabolism of food molecules begins when food enters the mouth,
as the enzyme salivary amylase initiates the breakdown of the
starch in foods. The entire process of digestion converts the large
polymers in food to monomers that can be absorbed. Starches are
broken down to monosaccharides, lipids are broken down to fatty
acids, and proteins are broken down to amino acids. These
monomers are absorbed into the bloodstream either directly, as is
the case with monosaccharides and amino acids, or repackaged in
intestinal cells for transport by an indirect route through lymphatic
vessels, as is the case with most fatty acids and other fat-soluble
molecules.
Once absorbed, water-soluble nutrients first travel to the liver
which controls their passage into the blood that transports the
nutrients to cells throughout the body. The fat-soluble nutrients
gradually pass from the lymphatic vessels into blood flowing to body
cells. Cells requiring energy or building blocks take up the nutrients
from the blood and process them in either catabolic or anabolic
pathways. The organ systems of the body require fuel and building
blocks to perform the many functions of the body, such as digesting,
absorbing, breathing, pumping blood, transporting nutrients in and
wastes out, maintaining body temperature, and making new cells.
Figure 8.3
Cellular
Metabolic
Processes
Metabolic
pathways of
a cell
The Atom | 465
Energy metabolism refers more specifically to the metabolic
pathways that release or store energy. Some of these are catabolic
pathways, like glycolysis (the splitting of glucose), β-oxidation
(fatty-acid breakdown), and amino acid catabolism. Others are
anabolic pathways, and include those involved in storing excess
energy (such as glycogenesis), and synthesizing triglycerides
(lipogenesis). Table 8.1 “Metabolic Pathways” summarizes some of
the catabolic and anabolic pathways and their functions in energy
metabolism.
Table 8.1 Metabolic Pathways
Catabolic
Pathways
Function
Anabolic
Pathways
Function
Glycolysis
Glucose breakdown
Gluconeogenesis
Synthesize
glucose
Glycogenolysis
Glycogen
breakdown
Glycogenesis
Synthesize
glycogen
β-oxidation
Fatty-acid
breakdown
Lipogenesis
Synthesize
triglycerides
Proteolysis
Protein breakdown
to amino acids
Protein
synthesis
Synthesize
proteins
Catabolism: The Breakdown
All cells are in tune to their energy balance. When energy levels are
high cells build molecules, and when energy levels are low catabolic
pathways are initiated to make energy. Glucose is the preferred
energy source by most tissues, but fatty acids and amino acids also
can be catabolized to release energy that can drive the formation
of ATP. ATP is a high energy molecule that can drive chemical
reactions that require energy. The catabolism of nutrients to release
energy can be separated into three stages, each containing
individual metabolic pathways. The three stages of nutrient
breakdown are the following:
466 | The Atom
• Stage 1. Glycolysis for glucose, β-oxidation for fatty acids, or
amino-acid catabolism
• Stage 2. Citric Acid Cycle (or Krebs cycle)
• Stage 3. Electron Transport Chain and ATP synthesis
Figure 8.4
ATP
Production
Pathway
“Aerobic
Production
Pathways” by
Boumphreyfr
/ CC BY-SA
3.0
The breakdown of glucose begins with glycolysis, which is a tenstep metabolic pathway yielding two ATP per glucose molecule;
glycolysis takes place in the cytosol and does not require oxygen. In
addition to ATP, the end-products of glycolysis include two threecarbon molecules, called pyruvate. Pyruvate can either be shuttled
to the citric acid cycle to make more ATP or follow an anabolic
pathway. If a cell is in negative-energy balance, pyruvate is
transported to the mitochondria where it first gets one of its
carbons chopped off, yielding acetyl-CoA. The breakdown of fatty
acids begins with the catabolic pathway, known as β-oxidation,
which takes place in the mitochondria. In this catabolic pathway,
four enzymatic steps sequentially remove two-carbon molecules
from long chains of fatty acids, yielding acetyl-CoA molecules. In the
case of amino acids, once the nitrogen is removed from the amino
acid the remaining carbon skeleton can be enzymatically converted
into acetyl-CoA or some other intermediate of the citric acid cycle.
Acetyl-CoA, a two-carbon molecule common to glucose, lipid, and
protein metabolism enters the second stage of energy metabolism,
the citric acid cycle.
The Atom | 467
In the citric acid cycle, acetyl-CoA is joined to a four-carbon
molecule. In this multistep pathway, two carbons are lost as two
molecules of carbon dioxide. The energy obtained from the breaking
of chemical bonds in the citric acid cycle is transformed into two
more ATP molecules (or equivalents thereof) and high energy
electrons that are carried by the molecules, nicotinamide adenine
dinucleotide (NADH) and flavin adenine dinucleotide (FADH2).
NADH and FADH2 carry the electrons to the inner membrane in the
mitochondria where the third stage of energy release takes place,
in what is called the electron transport chain. In this metabolic
pathway a sequential transfer of electrons between multiple
proteins occurs and ATP is synthesized. The entire process of
nutrient catabolism is chemically similar to burning, as carbon and
hydrogen atoms are
combusted (oxidized) producing carbon
dioxide, water, and heat. However, the stepwise chemical reactions
in nutrient catabolism pathways slow the oxidation of carbon atoms
so that much of the energy is captured and not all transformed into
heat and light. Complete nutrient catabolism is between 30 and 40
percent efficient, and some of the energy is therefore released as
heat. Heat is a vital product of nutrient catabolism and is involved in
maintaining body temperature. If cells were too efficient at trapping
nutrient energy into ATP, humans would not last to the next meal, as
they would die of hypothermia (excessively low body temperature).
Anabolism: The Building
The energy released by catabolic pathways powers anabolic
pathways in the building of macromolecules such as the proteins
RNA and DNA, and even entire new cells and tissues. Anabolic
pathways are required to build new tissue, such as muscle, after
prolonged exercise or the remodeling of bone tissue, a process
involving both catabolic and anabolic pathways. Anabolic pathways
also build energy-storage molecules, such as Glycogen and
468 | The Atom
triglycerides. Intermediates in the catabolic pathways of energy
metabolism are sometimes diverted from ATP production and used
as building blocks instead. This happens when a cell is in positiveenergy balance. For example, the citric-acid-cycle intermediate,
α-ketoglutarate can be anabolically processed to the amino acids
glutamate or glutamine if they are required. The human body is
capable of synthesizing eleven of the twenty amino acids that make
up proteins. The metabolic pathways of amino acid synthesis are
all inhibited by the specific amino acid that is the end-product of a
given pathway. Thus, if a cell has enough glutamine it turns off its
synthesis.
Anabolic pathways are regulated by their end-products, but even
more so by the energy state of the cell. When there is ample energy,
bigger molecules, such as protein, RNA and DNA, will be built as
needed. Alternatively, when energy is insufficient, proteins and
other molecules will be destroyed and catabolized to release energy.
A dramatic example of this is seen in children with marasmus,
a form of advanced starvation. These children have severely
compromised bodily functions, often culminating in death by
infection. Children with marasmus are starving for calories and
protein,
which
are
required
to
make
energy
and
build
macromolecules. The negative-energy balance in children who have
marasmus results in the breakdown of muscle tissue and tissues of
other organs in the body’s attempt to survive. The large decrease
in muscle tissue makes children with marasmus look emaciated or
“muscle-wasted.”
The Atom | 469
Figure 8.5
Metabolic
Pathway of
Gluconeogen
esis
In a much less severe example, a person is also in negative-energy
balance between meals. During this time, blood-glucose levels start
to drop. In order to restore blood-glucose levels to their normal
range, the anabolic pathway, called gluconeogenesis, is stimulated.
Gluconeogenesis is the process of building glucose molecules
mostly from certain amino acids and it occurs primarily in the liver
(Figure 8.5 “Metabolic Pathway of Gluconeogenesis”). The liver
exports the synthesized glucose into the blood for other tissues to
use.
470 | The Atom
Energy Storage
In contrast, in the “fed” state (when energy levels are high), extra
energy from nutrients will be stored. Glucose is stored mainly in
muscle and liver tissues. In these tissues it is stored as glycogen, a
highly branched macromolecule consisting of thousands of glucose
molecules held together by chemical bonds. The glucose molecules
are joined together by an anabolic pathway called glycogenesis.
For each molecule of glucose stored, one molecule of ATP is used.
Therefore, it costs energy to store energy. Glycogen levels do not
take long to reach their physiological limit and when this happens
excess glucose will be converted to fat. A cell in positive-energy
balance detects a high concentration of ATP as well as acetyl-CoA
produced by catabolic pathways. In response, the rate of catabolism
is slowed or shut off and the synthesis of fatty acids, which occurs
by an anabolic pathway called lipogenesis, is turned on. The newly
made fatty acids are transported to fat-storing cells called
adipocytes where they are stored as triglycerides. Fat is a better
alternative to glycogen for energy storage as it is more compact (per
unit of energy) and, unlike glycogen, the body does not store water
along with fat. Water weighs a significant amount, and increased
glycogen stores, which are accompanied by water, would
dramatically increase body weight. When the body is in positiveenergy balance, excess carbohydrates, lipids, and protein can all be
metabolized to fat.
The Atom | 471
Learning Activities
Technology Note: The second edition of the Human
Nutrition Open Educational Resource (OER) textbook
features interactive learning activities. These activities are
available in the web-based textbook and not available in the
downloadable versions (EPUB, Digital PDF, Print_PDF, or
Open Document).
Learning activities may be used across various mobile
devices, however, for the best user experience it is strongly
recommended that users complete these activities using a
desktop or laptop computer.
An interactive H5P element has been excluded
from this version of the text. You can view it
online here:
humannutrition2e22/?p=288#h5p-82
An interactive H5P element has been excluded
from this version of the text. You can view it
472 | The Atom
online here:
humannutrition2e22/?p=288#h5p-83
The Atom | 473
Weight Management
Photo by
Hope House
Press on
unsplash.co
m / CC0
https://unspl
ash.com/
photos/
PJzc7LOt2Ig
“Obesogenic” is a word that has sprung up in the language of public
health professionals in the last two decades. The Centers for
Disease Control and Prevention (CDC) defines obesogenic as “an
environment that promotes increased food intake, non-healthful
1
foods, and physical inactivity.”
The CDC reports that in 2009 in the United States, 33 percent of
1. Obesogenic Environments. Center for Disease Control
and Prevention (CDC). https://www.cdc.gov/pcd/
issues/2015/14_0559.htm. Published 2013. Accessed
September 22, 2017.
474 | Weight Management
adults and 16 percent of children were obese, a doubling and tripling
of the numbers since 1980, respectively, while in Hawai‘i the obesity
rate was 23.8% in 2016 with 40.8% of those individuals being Native
2
Hawaiians.
The health consequences of too much body fat are numerous,
including increased risks for cardiovascular disease, Type 2
diabetes, and some cancers. The medical costs related to obesity
are well over one hundred billion dollars and in Hawai‘i, over $470
million is spent annually. On the individual level, people who are
obese spend $1,429 more per year for medical care than people of
healthy weight.
Numerous obesogenic agents that contribute to this immense
public health problem have become a part of everyday life in
American society. The fast food industry has been growing for
decades and continues to grow despite the latest economic slump.
In America today there are over twelve thousand McDonald’s
restaurants, while in 1960 there was one. Food portions have been
getting bigger since the 1960s, and in the 1990s North American
society experienced the “super-size” marketing boom, which still
endures. Between 1960 and 2000 more than 123 million vehicles
were added to the American society. Escalators, elevators, and
horizontal walkways now dominate shopping malls and office
buildings, factory work has become increasingly mechanized and
robotized, the typical American watches more than four hours of
television daily, and in many work places the only tools required
to conduct work are a chair and a computer. The list of all the
societal obesogenic factors goes on and on. They are the result
of modernization, industrialization, and urbanization continuing on
2. Hawaii State Obesity Data, Rates, and Trends. The State
of Obesity: Better Policies for a Healthier America.
https://stateofobesity.org/states/hi/. Published August
2017. Accessed September 22, 2017.
Weight Management | 475
without
individuals,
public
health
officials,
or
government
adequately addressing the concurrent rise in overweight and
obesity.
With obesity at epidemic proportions in America it is paramount
that policies be implemented or reinforced at all levels of society,
and include education, agriculture, industry, urban planning,
healthcare, and government. Reversing and stopping obesity are
two different things. The former will require much more societal
and individual change than the latter. The following are some ideas
for constructing an environment in America that promotes health
and confronts the obesity epidemic:
Individual Level
• Purchase less prepared foods and eat more whole foods.
• Decrease portion sizes when eating or serving food.
• Eat out less, and when you do eat out choose low-calorie
options.
• Walk or bike to work. If this is not feasible, walk while you are
at work.
• Take the stairs when you come upon them or better yet, seek
them out.
• Walk your neighborhood and know your surroundings. This
benefits both health and safety.
• Watch less television.
Community Level
• Request that your college/workplace provides more access to
healthy low-cost foods.
• Support changes in school lunch programs.
• Participate in cleaning up local green spaces and then enjoy
them during your leisure time.
• Patronize local farms and fruit-and-vegetable stands.
• Talk to your grocer and ask for better whole-food choices and
seafood at a decent price.
476 | Weight Management
• Ask the restaurants you frequently go to, to serve more
nutritious food and to accurately display calories of menu
items.
National Level
• Support policies that increase the walkability of cities.
• Support national campaigns addressing obesity, such as
America on the Move.
• Support policies that support local farmers and the increased
access and affordability of healthy food.
Some scientists predict that the childhood obesity rate will reach
100 percent by 2044. It is critical for the nation’s health to change
our environment to one that promotes weight loss and/or weight
maintenance. However, action is needed on multiple fronts to
reverse the obesity epidemic trend within one generation.
In this section you will learn how to assess body weight and
fatness. You will also learn that it is not only society and
environment that play a role in body weight and fatness, but also
physiology, genetics, and behavior—and that all of them interact.
We will also discuss the health risks of being underweight and
overweight, learn evidence-based solutions to maintain body
weight at the individual level, and assess the current state of affairs
of combating the obesity epidemic in the United States.
Weight Management | 477
Balancing Energy Input with Energy Output
Photo by Jon
Flobrant on
unsplash.co
m / CC0
https://unspl
ash.com/
photos/_r19
nfvS3wY
To Maintain Weight, Energy Intake Must Balance
Energy Output
Recall that the macronutrients you consume are either converted to
energy, stored, or used to synthesize macromolecules. A nutrient’s
metabolic path is dependent upon energy balance. When you are in
a positive energy balance the excess nutrient energy will be stored
or used to grow (e.g., during childhood, pregnancy, and wound
healing). When you are in negative energy balance you aren’t taking
in enough energy to meet your needs, so your body will need to use
its stores to provide energy. Energy balance is achieved when intake
of energy is equal to energy expended. Weight can be thought of as
a whole body estimate of energy balance; body weight is maintained
when the body is in energy balance, lost when it is in negative
energy balance, and gained when it is in positive energy balance.
In general, weight is a good predictor of energy balance, but many
other factors play a role in energy intake and energy expenditure.
Some of these factors are under your control and others are not. Let
478 | Weight Management
us begin with the basics on how to estimate energy intake, energy
requirement, and energy output. Then we will consider the other
factors that play a role in maintaining energy balance and hence,
body weight.
Estimating Energy Requirement
To maintain body weight you have to balance the calories obtained
from food and beverages with the calories expended every day.
Here, we will discuss how to calculate your energy needs in
kilocalories per day so that you can determine whether your caloric
intake falls short, meets, or exceeds your energy needs. The
Institute of Medicine has devised a formula for calculating your
Estimated Energy Requirement (EER). It takes into account your
age, sex, weight, height, and physical activity level (PA). The EER is
a standardized mathematical prediction of a person’s daily energy
needs in kilocalories per day required to maintain weight. It is
calculated for those over 18 years of age via the following formulas:
Adult male: EER = 662 − [9.53 X age (y)] + PA X [15.91 X wt (kg) +
5.39.6 X ht (m)]
Adult female: EER = 354 − [6.91 x age (y)] + PA x [9.36 x wt (kg) +
726 x ht (m)]
Note: to convert pounds to kilograms, divide weight in pounds by
2.2. To convert feet to meters, divide height in feet by 3.3.
Estimating Caloric Intake
To begin your dietary assessment, go to MyPlate, which is available
on
the
US
Department
of
Agriculture
(USDA)
website:
http://www.choosemyplate.gov/.
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