Why Are We Obese or Severely Overweight?
Causes of Obesity
Weight gain occurs when a person consumes
more calories than he or she burns. A minor calorie surplus leads to overweight,
while a major energy surplus causes obesity. But what causes this imbalance
between calories in and calories in the first place may differ from one
person to another. Genetic, environmental, psychological, and other factors
all play a part. Here are some of the more common causes of obesity.
Causes of Obesity - Genetics
Obesity tends to run in families, implying
genetic factors. The search for an "obesity gene" is complicated,
however, by the fact that families also tend to share eating and lifestyle
habits, making it difficult to separate genetics per se from behavior.
Studies have been designed to determine
how significantly genes and family lifestyles affect obesity. Some studies
of adopted children indicate that genetics and heredity do play some role.
Adopted children tend to develop weight
problems similar to their biological, rather than adoptive, parents.
But although children of obese parents
have a 25-30 percent extra likelihood of becoming obese themselves, part
of this increased risk of obesity may be due to eating habits and poor
family nutrition, rather than heredity.
Causes of Obesity - Genetic Predisposition
to be Overweight Rather than Obese
Many studies have found a genetic link
to obesity, showing that the pattern of deposition of fat - i.e. the way
fat builds up around the body - and the degree of overweight can both
be inherited.
Body shape, for example, generally falls
into one of three categories - ectomorph, endomorph or mesomorph. The
slighter frames of ectomorphs reflect a low capacity for fat storage.
Endomorphs have the most fat-storage capacity. And mesomorphs have an
ability to store fat that falls somewhere in between. Fat storage is also
more evenly distributed. These are stereotype body shapes. In practice,
most people are a combination of all three, with a disposition to be more
like one or two of them. It is doubtful whether a person's body shape
and fat distribution is sufficient to cause obesity.
Causes of Obesity - Genes - Body Shape
Other research has shown that often normal-weight
children of obese parents have a lower metabolic rate (they tend to burn
more calories than average even when they're asleep, or else they burn
fewer calories for the same physical activity) than normal-weight children
of non-obese parents. Again, this suggests that the susceptibility to
obesity can also be inherited. But the fact that obesity has increased
so much in the last few decades appears to discount genetics as the main
cause.
Causes of Obesity - Genetics - Leptin
In her book, The Hungry Gene, Ellen Shell
promoted the idea that leptin - a naturally occuring hormone that controls
the appetite - may be one of the causes of obesity. When full, fat cells
release the hormone leptin, which curbs appetite. If leptin production
is hindered, the fat cells are unable to signal that they're full, and
weight gain occurs. Research into leptin is only just beginning, although
the leptin-obesity link appears to have been disproved by some initial
studies.
Causes of Obesity - Genes - Hormones
A small minority of cases of obesity can
be explained by glandular or hormonal problems. One such problem is clinical
hypothyroidism, where there is not enough thyroid hormone to control normal
rates of metabolism. Also, Cushing's Syndrome, where the production of
the corticosteroid hormones is abnormal.
Sex hormones can also affect obesity. In
women, body fat levels during adolescence, pregnancy and the menopause
are determined by the balance of female sex hormones. Changes in energy
intake, desire for food and specific cravings occur at various stages
of the menstrual cycle. Some women appear to be more susceptible than
others to hormonal changes and many overweight women cite pregnancy as
the time when their problem started.
Causes of Obesity - Genetics - Summary
Genetics and weight (and thus obesity)
are inextricably linked. The question is, to what extent can the explosion
of overweight and the modern levels of obesity be attributed to genes?
According to Stephen O'Rahilly, professor of clinical biochemistry and
medicine at Cambridge University, the influence of genetics on modern
levels of obesity is insignificant:
"Nothing genetic explains the rise
in obesity. We can't change our genes over 30 years."
Causes of Obesity - Gender
Weight is affected by gender. Men have
more lean body mass (muscle) and less fat than women. Lean body mass is
more metabolically active and thus uses more energy (calories) than fat.
So even at rest, men burn between 10 and 20 percent more calories than
women. However, while women are more predisposed to gaining weight than
men, this gender-induced susceptibility to gain weight cannot account
for the obesity problem.
Causes of Obesity - Environmental factors
Environment also strongly influences obesity.
An environment where people eat high fat and high sugar diets and take
little exercise, causes more problems with excess weight and obesity than
one where people eat low fat diets and get regular exercise. Americans
live in an environment that marginalizes the obese while simultaneously
creating the perfect environment for weight gain as a result of it's fast-food
and convenience-food culture. Also, due to it's culture of convenience,
TV and labor-saving devices, most Americans do not get enough physical
activity which is another prime environmental cause of obesity and weight
gain.
Causes of Obesity - Psychological Factors
- Psychological factors may also influence
eating habits. A number of psychological factors and behavioral problems
may cause people to gain weight. Many people over eat when they're stressed,
bored or angry. Over time, the association between an emotion and food
can become firmly fixed.
- Although research indicates that most
overweight people have no more psychological problems than people of
average weight, it is estimated that up to 10 percent of people who
are mildly obese and try to lose weight repetitively have binge eating
disorder. During an episode of binge eating, people eat large quantities
of food with no sense of self-control. Those with the most severe binge
eating problems are also likely to have symptoms of depression and low
self-esteem. These people have more difficulty losing weight and keeping
it off than people without binge eating problems.This disorder is even
more common in people who are severely obese.
- Depression and stress can lead to obesity.
They are leading causes of eating disorders. Indeed, most eating disorders
can be traced to behavioral or psychological difficulties. Even lack
of confidence can lead to social withdrawal and a sedentary-type lifestyle
that promotes weight gain and ultimately obesity.
Causes of Obesity - Illness and/or Drugs
Some illnesses can lead to obesity or a
tendency to gain weight. These include hypothyroidism, Cushing's syndrome,
depression, and certain neurological problems that can lead to overeating.
Also, drugs such as steroids and some antidepressants may cause weight
gain. A doctor can tell whether there are underlying medical conditions
that are causing weight gain or making weight loss difficult.
Causes of Obesity - Lack of Physical Activity
As stated above, weight gain occurs when
a person consumes more calories than he or she burns. So far we have dealt
with an excess of energy/calories IN. But lack of calories OUT is also
one of the major causes of weight gain and obesity. Lack of physical activity
caused in part by watching too much TV, or playing too many computer games
is strongly associated with obesity levels, especially in young people.
Causes of Obesity - Summary
Obesity is a complex issue and a serious
illness rather than simply a weight condition. The causes of obesity are
various and often interlinked - one reason that weight loss drugs or simple
dieting, by themselves, are usually inadequate to treat those suffering
from obesity. Typically, obesity treatment involves a combination of diet,
exercise, medication and counseling. Even then, long term results of such
obesity treatment are mixed.
If You Suffer from Obesity - the First
Step
If you suffer from obesity, your first
step should be to seek professional help. |
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