24
those with greatly enhanced muscle mass, should have much
higher BMRs than nonathletes, there is little difference between
those of the same gender and body surface area.
Total Metabolic Rate (TMR)
Te
total metabolic rate (TMR)
is the rate of kilocalorie con-
sumption needed to fuel
all
ongoing activities—involuntary
the person oFen loses weight. Bones weaken and muscles, in-
cluding the heart, begin to atrophy.
In contrast,
hypothyroidism
results in slowed metabolism,
obesity, and diminished thought processes.
Physical Training
Surprisingly, physical training has little ef-
fect on BMR. Although it would appear that athletes, especially
942
Fat
—unwanted,
unloved
, and yet of-
ten overabundant. Besides the
physical
toll
, the
social stigma
and economic
disadvantages of obesity are legendary. A
fat person pays higher insurance premiums,
is discriminated against in the job market,
has fewer clothing choices, and endures fre-
quent humiliation throughout life.
What Causes Obesity?
It’s a fair bet that few people choose to
become obese. So what causes it? Some
possibilities are:
1. Overeating during childhood pro-
motes adult obesity.
Some believe that
the “clean your plate” order sets the
stage for adult obesity by increasing the
number of adipose cells formed during
childhood. The more adipose cells there
are, the more fat can be stored.
2. Obese people are more fuel
efficient and more effective “fat
storers.”
Although it is often assumed
that people who are obese eat more,
this is not necessarily true—many
actually eat less than people of
normal weight. When yo-yo dieters
lose weight, their metabolic rate falls
sharply. But, when they subsequently
gain weight, their metabolic rate
temporarily increases like a furnace
being stoked. Each successive weight
loss occurs more slowly, but they regain
weight three times as fast.
Furthermore, fats pack more wallop
per calorie (are more fattening) than
proteins or carbohydrates because of
the way the body processes them. If we
ingest 100 excess carbohydrate calories,
23 are used in metabolic processing and
77 are stored. However, if the 100 excess
calories come from fat, only 3 calories are
“burned” and the rest (97) are stored.
These facts apply to everyone, but
when you are obese the picture is even
bleaker. “Fat” fat cells of overweight
people:
Sprout more alpha receptors, which
favor fat accumulation.
Send different molecular messages
than “thin” fat cells. They spew
out inflammatory cytokines (tumor
necrosis factor and others) that can
promote insulin resistance and they
release less adiponectin, a hormone
that improves the action of insulin
in glucose uptake and storage.
Have exceptionally efficient
lipoprotein lipases, which unload
fat from the blood (usually to
fat cells).
Although it would appear that the
so-called satiety chemicals (hormones
and others) should prevent massive fat
deposit, this seems not to be the case
in obese people. It may be that excess
weight promotes not only insulin
resistance but leptin resistance as well.
Obesity: Magical Solution Wanted
3. Genetic predisposition.
Morbid
obesity is the destiny of those
inheriting two obesity genes. These
people, given extra calories, will always
lay them down as fat, as opposed to
those that lay down more muscle with
some of the excess. However, a true
genetic predisposition for “fatness”
appears to account for only about 5%
of obese Americans.
4. Viral infection.
Surprisingly, a recent
study has shown a link between obesity
and infection with a particular cold virus
(adenovirus 360). The virus has been
shown to increase the number and
fat content of adipocytes in laboratory
animals, but further studies are needed
to determine if there is a true cause-effect
relationship in humans.
Treatments—The Bad
and the Good
Some so-called treatments for obesity are
almost more dangerous than the disease
itself. Unfortunate strategies include the
following.
1. “Water pills.”
Diuretics prompt the
kidneys to excrete more water and may
cause a few pounds of weight loss for a
few hours. They can also cause serious
dehydration and electrolyte imbalance.
2. Diets.
Diet products and books
sell well, but do they work and are
they safe? There is a long-standing
duel between those promoting low-
carbohydrate (high-protein and -fat)
regimens such as the Atkins and South
Beach diets, and those espousing
the traditional low-fat (high–complex
carbohydrates) diet.
Clinical studies show that people
on the low-carbohydrate diets lose
weight more quickly at first, but
plateau at 6 months. They seem to
preferentially lose fat from the body
trunk, a weight distribution pattern (the
A
C L O S E R
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