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The balance between calorie
intake and energy expenditure determines a person's
weight. If a person eats more calories than he or
she burns, the person gains weight
(the body will store the
excess energy as fat). If a person eats fewer
calories than he or she burns, he or she will lose
weight. Therefore the most common causes of obesity
are overeating and physical inactivity. At present,
we know that there are many factors that contribute
to obesity, some of which have a genetic component:
Genetics. A person is more likely to develop
obesity if one or both parents are obese. Genetics
also affect hormones involved in fat regulation. For
example, one genetic cause of obesity is leptin
deficiency. Leptin is a hormone produced in fat
cells, and also in the placenta. Leptin controls
weight by signaling the brain to eat less when body
fat stores are too high. If, for some reason the
body cannot produce enough leptin, or leptin cannot
signal the brain to eat less, this control is lost,
and obesity occurs. The role of leptin replacement
as a treatment for obesity is currently being
explored.
Overeating. Overeating leads to weight gain,
especially if the diet is high in fat. Foods high in
fat or sugar (e.g., fast
food, fried food and sweets,) have high
energy density (foods that
have a lot of calories in small amount of food).
Epidemiology studies have shown that diets high in
fat contribute to weight gain.
A diet high in simple carbohydrates. The role of
carbohydrates in weight gain is not clear.
Carbohydrates increase blood glucose levels, which
in turn stimulate insulin release by the pancreas,
and insulin promotes the growth of fat tissue and
can cause weight gain. Some scientists believe that
simple carbohydrates (sugars,
fructose, desserts, soft drinks, beer, wine, etc.)
contribute to weight gain because they are more
rapidly absorbed into the blood stream than complex
carbohydrates (pasta, brown
rice, grains, vegetables, raw fruits, etc.)
and thus cause a more pronounced insulin release
after meals than complex carbohydrates. This higher
insulin release, some scientists believe, contribute
to weight gain.
Frequency of eating. The
relationship between frequency of eating
(how often you eat)
and weight is somewhat controversial. There are
many reports of overweight people eating less
often than people with normal weight. Scientists
have observed that people who eat small meals four
or five times daily, have lower cholesterol levels
and lower and/or more stable blood sugar levels
than people who eat less frequently
(two or three) large
meals daily. One possible explanation is that
small frequent meals produce stable insulin
levels, whereas large meals cause large spikes of
insulin after meals.
Slow metabolism. Women have less muscle than men.
Muscle burns more calories than other tissue
(which includes fat).
As a result, women have a slower metabolism than
men, and hence, have a tendency to put on more
weight than men, and weight loss is more difficult
for women. As we age, we tend to lose muscle and
our metabolism slows, therefore, we tend to gain
weight as we get older particularly if we do not
reduce our daily caloric intake. Physical
inactivity. Sedentary people burn fewer calories
than people who are active. The National Health
and Examination Survey (NHANES)
showed that physical inactivity was strongly
correlated with weight gain in both sexes.
Medications. Medications
associated with weight gain include certain
antidepressants (medications
used in treating depression),
anti-convulsants (medications
used in controlling seizures such as carbamazepine
and valproate), diabetes medications
(medications used in
lowering blood sugar such as insulin,
sulfonylureas and thiazolidinediones),
certain hormones such as oral contraceptives and
most corticosteroids such as Prednisone. Weight
gain may also be seen with some high blood
pressure medications and antihistamines.
Psychological factors. For some people, emotions
influence eating habits. Many people eat
excessively in response to emotions such as
boredom, sadness, stress or anger. While most
overweight people have no more psychological
disturbances than normal weight people, about 30
percent of the people who seek treatment for
serious weight problems have difficulties with
binge eating.
Diseases such as hypothyroidism, insulin
resistance, polycystic ovary syndrome and
Cushing's syndrome are also contributors to
obesity. |
