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ENVIRONMENTAL
AND GENETIC INFLUENCES ON OBESITY
By Tiffany
Quilter
 Over
the last several years, the United States
has seen an increase in obesity rates.
Sixty-four percent of women and seventy-four
percent of men are either overweight
or obese (1).
There are many reasons that people become
obese. Overeating and inactivity are
two primary causes of obesity. However,
some will say they are obese because
it is in their genes. This paper will
address whether hereditary factors play
a role in obesity, or whether it is
simply a matter of caloric imbalance.
Hippocrates
is credited with being one of the first
physicians to encourage physical activity
for health. He stated "that which
is used develops, and that which is
not used wastes away," referring
to food and exercise. Booth and Lees
discuss the genetic factors that are
affected by physical inactivity (2).
It is known that human ancestors participated
in substantial amounts of physical activity
to eat and survive. Booth and Lees explain
that human genes have changed, or adapted
over time to the environment.
In recent
years, humans have become less physically
active, and it appears that our genes
are maladapting. This is represented
by obesity, type II diabetes, and other
obesity related diseases. It has been
found that children are more likely
to develop obesity related diseases
if their parents had the disease. So,
are genes becoming maladapted to physical
inactivity and how can gene expression
and research help in understanding or
detecting possible disease risks? Booth
and Lees suggest that it is a valid
endeavor to find what genes are expressed
with inactivity and what genes predispose
an individual to obesity related diseases.
(2)
Several studies
have evaluated the effects of heredity
on obesity rates and obesity related
diseases. Bulik et al. conducted a study
that compared genetic and environmental
factors to obesity and binge eating
in 854 pairs of female twins (3).
Participants were interviewed to determine
binge eating habits, and self reported
height and weight were collected. From
the data collected, they determined
that since obesity was observed without
binge eating habits, and vice versa,
obesity was more related to genetics
than it was to environmental factors.
(3)
Sorensen
et al. also evaluated the genetic effects
of obesity in adults that had been adopted
compared to their biological siblings
raised by their natural parents (4).
Adoptees and biological full and half
siblings were sent questionnaires to
determine current height, weight, and
other health issues. Subjects that responded
included 3,580 adoptees and 965 siblings.
They found that the adoptees that were
more obese had full siblings that also
had high body mass indexes (BMI). They
also found a small relationship between
the adoptees and their half siblings.
The researchers conclude that there
are genetic factors that contribute
to obesity regardless of the environment
that an individual is raised in. (4)
The Pima
Indians are population that has been
studied on the effects of obesity related
to genetics and the environment. Weyer
et al. compared 7 male Caucasians (C)
and 7 male Pima Indians (PI), 3 lean
and 4 obese in each group (5).
They were tested on energy metabolism
following 48 hours of overfeeding and
fasting. Following baseline measures
they were tested in three different
conditions: eucaloric (100% of energy
requirements), fasting (0%), and overfed
(200%). They found that the C group
was significantly taller than the PI
group, but there was no difference in
body composition. The PI group did not
have an impaired metabolic response
to short term overfeeding compared to
the C group. The researchers conclude
that this metabolic response may be
related to the high obesity rate in
this population. (5)
There is
some debate in the literature as to
the degree of impact genetics has on
obesity compared to physical inactivity.
The American College of Sports Medicine
(ACSM) recommends that individuals participate
in 150-250 minutes per week of physical
activity to maintain weight, and more
than 250 minutes per week in order to
lose weight (6).
Evidence shows that reductions in weight
can significantly improve health and
decrease risk of disease. Lifestyle
changes in physical activity and diet
restriction can reduce weight and increase
longevity. (6)
Lifestyle
habits of physical activity have been
shown to positively influence healthy
body weight. Bassett et al. evaluated
the physical activity levels of 98 Old
Order Amish adults between 18 and 75
years old (7).
They found that the Amish men and women
had very high physical activity levels.
The men accumulated about 18,425 steps
per day and the women accumulated about
14,196 steps per day. All of the Amish
subjects exceeded the ACSM guidelines
for physical activity. The prevalence
of obesity was 0% and 9% and overweight
was 25% and 27% for men and women respectively.
This is lower compared to the general
United States statistics. The researchers
conclude that the difference in obesity
rates is related to the increased amount
of physical activity that is part of
the Amish lifestyle. (7)
Mediterranean
populations also have a lower prevalence
of obesity. Schroder et al. conducted
a study to determine how the Mediterranean
diet affects body mass index in Spanish
men and women (1547 men, 1615 women)
(8). Mediterranean
diets generally consist of vegetables,
fruits, pulses, nuts, fish, meant, cereals,
olive oil and wine. Schroder et al.
found that higher consumption of fruits,
fish, legumes, nuts, and olive oil,
and lower consumption of meat, sweets,
and pastries was associated with individuals
who adhered to a Mediterranean diet.
They also found that both males and
females who adhered to the Mediterranean
diet were less obese than those who
did not. The researchers conclude that
healthy eating habits are related to
decreased obesity rates.(8)
Christakis
and Fowler conducted a study to determine
how obesity is contributable to person-to-person
spread (9).
Individuals who were offspring and "close
friends" of the Framingham heart
study cohort were recruited (N=5,124).
They found that the obesity epidemic
could be a factor of the spread of obesity
in a social network, friend to friend
and among siblings. They conclude that
this social effect could positively
or negatively alter the progression
of the obesity epidemic in the country
and the world. (9)
Obesity throughout
the United States and the world is definitely
becoming a problem and a health risk
for many individuals. The problem seems
to come from several factors. Genetics
play a role in the predisposition to
obesity and obesity related diseases.
Physical inactivity and poor diet cause
weight gain and increased health risk.
Social networking factors contribute
to the likelihood of becoming obese.
The problem does not come from just
one of these factors but is a combination
of all three.
If a person
is genetically predisposed to become
obese, then they need to be aware that
they will need to work harder and be
more conscious of staying healthy. If
a person is in an environment that encourages
physical inactivity and poor diet then
they also need to be educated and made
aware of the consequences of following
those habits. It is up to health educators
and healthy individuals to encourage
others to become more physically active
and live a healthy lifestyle regardless
of predisposition or environmental influences.
references
Biography:
Tiffany is currently an Exercise Science
graduate student at Central Washington
University. She also coaches the throwers
on the track team at Moses Lake High
School. She received a Bachelor of Science
in Exercise Science from Central Washington
University while also competing on the
track team. She is married and has one
beautiful daughter that keeps her busy.
She hopes to be able to make a difference
in the world by encouraging physical
activity and promoting healthy lifestyles
through modification of, and education
about, our built and natural enviroments.
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