Keywords: adiposty obesity genetics diet exercise research
Lines: 958
Organization: Omen Technology, Portland
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1. FOREWORD
This is a summary of information on the causes and treatment
of overweight I've gleaned over the years from forays to the
Med School library and from other sources. I hope this
summary provides useful information on obesity. Some of you
may be able to fill in gaps mentioned here.
2. BACKGROUND
Adipose Cell: There are two types of adipose (fat) cell,
White Adipose Tissue (WAT) and Brown Adipose Tissue (BAT).
Set Point Theory: A biological servo system controls energy
expenditures, fat cell receptors, appetite, and other
physical characteristics to return the body to a constant
weight (set point) after periods of starvation or
overfeeding.
Rats and pigs are commonly used in adiposty research because
their fat mechanisms closely resemble those of humans.
Body Mass Index (BMI) is a measure of the percentage of fat
to total body mass. BMI is used as a height and bone-
density independent measure of adiposty.
Morbid obesity: Obesity severe enough to directly limit the
victim's health or quality of life.
Refactory: Adjective indicating the condition reasserts
itself, precluding long term relief.
3. TYPES OF ADIPOSTY
One source of obesity is overeating from emotional stress.
Experiments with controlled overfeeding of lean subjects
demonstrate an increase in body metabolism that restores
normal weight when overfeeding ceases.
In a 1986 Dutch study, some men who experienced many life
events in a short period showed a gain in body mass. A year
later this weight gain had disappeared in almost all
subgroups, EXCEPT those that tried to lose weight by
dieting.
My area of interest is chronic adiposty, in which the
subject is heavier than average most of his life.
Adiposty 101
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4. THE BIOLOGY OF ADIPOSTY
4.1 Brown Adipose Tissue (BAT)
Brown Adipose Tissue (BAT) generates heat (thermogenisis) by
burning calories without physical motion.
4.2 White Adipose Tissue (WAT)
Obesity results from an excess of white adipose tissue
(WAT).
WAT cells are not simple storage tanks. These are active,
living cells. They convert steroid hormones to estrogen.
White Fat cells compete with lean tissue for nutrients,
interfering with normal muscle development.
The fact that reduction of fat cell numbers (see below)
causes permanent fat loss while weight loss techniques that
do not reduce the number of fat cells are temporary suggests
that the white fat cells themselves are the "set point"
regulator.
4.3 Preadipocytes > Fat Cells
White fat cells begin life as PREADIPOCTYES.
Adipose tissue from {*filter*} humans contains a pool of tiny
precursor cells (preadipocytes) which can be converted to
adipocytes (fat cells) in the presence of glucocorticoids
and insulin. (Journal of Clinical Endocrinology and
Metabolism, 1987).
The adiposty of individual pigs can be predicted by
measuring the ability of the suckling's {*filter*} to
differentiate preadipocytes into full size fat cells in a
test tube. The preobese sucklings had low levels of fetal
growth hormone and high levels of triiodothyronine.
4.3.1 Size and Number of Fat Cells Is obesity caused by an
excess number of fat cells or by gross enlargement of a
normal number of fat cells? The answer to this question has
heavy implications for the possible success of various
weight loss strategies.
A study published in the Proceedings of the 5th
International Congress on Obesity showed that obese subjects
who had lost weight in a combined diet/exercise program had
fat cells 25 per cent smaller than those of trained athletes
who had half the fat. In other words, the dieters had twice
as many fat cells as the athletes. (Dieting does not reduce
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the number of fat cells.)
4.4 Fat Cell Receptors
Fat cells gain and lose weight by passing lipids through
receptors. One type of receptor removes lipids from the
{*filter*} stream and another type allows the body to access the
energy stored in the fat cells with a resulting loss of
weight.
Geographic distribution of fat, including "love handles"
that do not respond to extreme dieting, is believed to
result from local variations in these receptors. No diet or
exercise has been shown to have geographic specificity in
fat reduction.
The numbers and efficiencies of the two receptor types
change with repeated dieting, promoting weight gain.
4.5 Muscle Fibre Type
The April 19 1990 Lancet reports that skeletal muscle fibre
type is directly correlated with BMI. Lean subjects have
more "slow fibers" well endowed with mitochondria that use
fatty acids as energy source. Corpulent subjects have more
"fast fibers" that cannot burn fat for energy. (See
EXERCISE, below.) (1D-5) (1D-7)
5. THE ROLE OF GENETICS
The conclusion of current research is that individual
differences in Body Mass Index (BMI) are mostly the result
of genetic factors.
Two studies published this year in the New England Journal
of Medicine illustrate the point.
In "The body-mass index of twins who have been reared
apart", the rearing environment was shown to have no effect
on BMI. In other words, if you're fat, it wasn't because
your mother fed you too many cookies and it wasn't because
your father didn't make you exercise.
In "The response to long-term overfeeding in identical
twins", 12 pairs of identical male twins were overfed and
kept sedentary under close supervision. There was a 3 to 1
ratio in weight gain between the easiest gainer and the
slowest gainer. Those who gained the most fat gained less
muscle than those who gained the least fat. Ten of the 12
pairs of identical twins gained almost identical amounts of
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weight.
This study is interesting because of its sample selection.
None of the subjects had any history of obesity whatsoever,
not even in their families. One can but imagine what that 3
to 1 spread would have been if subjects with a history of
weight problems had been included.
The appearance of these papers in the New England Journal of
Medicine prompted several submissions questioning the
papers' findings. These letters and the authors' replies
are printed in the Oct 11 1990 edition.
The Sep 1990 Science News reported a very wide difference in
the amounts and types of tissues added in response to
overfeeding. The thin people actually added more weight
than fat people did, but the thin people added weight mainly
as lean tissue instead of fat. Data from "lean hungry"
types that gained little weight were excluded.
5.1 The Role of Maternal Environment
What one's mother does or eats during or immediately before
pregnancy affects one's BMI. The May 1990 METABOLISM
reported that changes in the rat sow's diet during early
pregnancy had a permament effect on pups' lipid metabolism.
An Aug 5 1990 BBC broadcast reported that the size of a baby
relative to the size of the placenta had a greater
correlelation on {*filter*} {*filter*} pressure than the combined
effects of weight or {*filter*} consumption.
As reported in the Health InfoCom Network News Volume 3,
Number 36 December 5, 1990, Dr. Bernard Silverman of
Children's Memorial Hospital in Chicago says a study of
124 children whose mothers were either diabetic before
pregnancy or became diabetic during it showed: Children at
normal weight at age 1. Many were obese by 6 to 8. At 8,
the median weight was 71 pounds for boys; normal median -
56 pounds. Median for girls was 68 pounds; normal medium 55
pounds. Some researchers say the pre{*filter*}s' obesity may be
due to excess insulin in the amniotic fluid surrounding
them during gestation.
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5.2 The Role of Baby's Diet
A Case Western Reserve University rat study (4P-17) compared
rat pups fed a milk-substitute formula (56% of calories from
carbohydrates) with mother-fed controls (only 8% of calories
from carbohydrates). "The results show that alterations in
the source of calories rather than the total caloric intake
during the suckling period can have specific long-lasting
effects on lipid metabolism in {*filter*}hood, leading to the
development of obesity."
This result supports the assertion of a Reader's Digest
article that {*filter*} feeding can "Fat Proof" one's baby.
Left unanswered is the question: at what age should the
suckling's low carbohydrate diet evolve to the high
carbohydrate low fat diet favored by health authorities?
6. EFFECTS OF OBESITY
6.1 Personality Problems
The correlation between psychological problems and obesity
is well known. Many couches have been filled with patients
wishing to lose weight. As the nature and
...
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Adiposty 101 updated