It is difficult to define precisely the term obesity. Whereas insurance
companies publish reference tables that provide ideal weights in relation
to height and age, the decision as to who is overweight is still largely
subjective, but the Public Health Service recently reported that 33% of
Americans are 20% (or more) overweight. Interestingly enough, there are
marked sex and racial differences. About 40% of middle-aged White males
and 60% of middle-aged Black and Hispanic women are obese. Over the last
decade, the number of obese members of our population has increased by 8%!!
If the definition of obesity is difficult, the determination of its cause
is even more so. Is it scientifically acceptable for the physician to conclude
that an overweight patient just eats too much? Is obesity a disease?
The concept of an ideal physique differs among cultural groups and has changed
with time. A century ago, corpulence in many societies was viewed as a sign
of prosperity, and a matronly figure was the accepted norm for the homemaker.
Today, physical fitness is as much an ideal as portliness was decades ago,
and a slim silhouette is the mark of physical attractiveness among some,
but not all STRATA of our society, and among some racial groups.
Some people turn to food as a response to emotional problems. Compulsive
overeaters are a reality of life, and the outcome (obesity) tends to accentuate
their social problems. The aphorism "all the world loves a fat man,
because the fat man loves the world" is simply not true.
The availability of high calorie foods and the American love of fat (i.e.,
premium (12-15% fat) ice cream, Big Macs, french-fried potatoes) often contributes.
A fast food burger, fries and a coke constitute over half of ones caloric
needs for a day, and more than 2/3 of the saturated fat. Poor high fat,
high carbohydrate diets tend to be consumed by lower socioeconomic groups
because they are cheap and readily available.
The importance of heredity in predisposing to obesity is increasingly clear.
A few genetic syndromes that lead to obesity follow mendelian patterns of
inheritance, although these conditions are rare. Of greater general relevance
are the apparent polygenic influences on metabolism that seem to translate
into familial tendencies to obesity. Is the "fat" family a product
of its genes or a reflection of an over-zealous homemaker who derives pleasure
from watching the family eat? Studies of monozygotic twins who have reared
separately have demonstrated a strong hereditary influence on physique and
body weight.
A discussion of obesity must consider the issue of energy utilization. Is
obesity simply an imbalance between caloric supply and demand, or do people
inherently differ in the efficiency with which they use energy? The answer
to both questions is yes, but the interactions between genetic and environmental
factors are far from clear.
Different forms of obesity occur commonly in our population. These are:
Gluteal femoral obesity is thought by many scientists to result from
excessive caloric intake during the first year of life. In this setting,
fat cells proliferate to package the fats and triglycerides. Thus, there
are greater numbers of fat cells per unit volume or mass of tissue. This
form is difficult to MOBILIZE later in life and not many dieters are able
to eliminate their big hips and buttocks. Fortunately, the complications
and health effects of this form are substantially fewer than with types
1 to 3 above.
Pectoral girdle and abdominal/visceral adipority result from a distention
of individual fat cells as a result of caloric excess. It is readily mobilized
with diet. Of these forms visceral fat is the most "fluid". Middle
age men are particularly affected; the protuberant belly that I and so many
well fed men over age 30 contend with, is all to readily evident to us all.
Pectoral humoral adiposity occurs more commonly in females.
The Hip:Pelvic ratio is a commonly used measure. Those with H:P ratios of
greater than one (1) are at increased risk of developing diabetes mellitus,
heart disease and hypertension.
Public health physicians are expressing concern regarding the increasing
prevalence of childhood obesity in our society. It is generally concluded
that it represents excessive availability of high caloric food, and less
exercise. Because the incidence is increasing so dramatically, genetic predisposition
would not appear to be an important factor. From a public health perspective
its importance relates to the clear tendency for fat children to become
fat adults. Whether this represents a pattern of continued excessive caloric
intake, or an acquired aberration of metabolism is not so evident.
Aging poses another problem. In males, there is a gradual decrease in testosterone
and growth hormone production with age. As a result, muscle mass gradual
decreases, and it responds much less readily to exercise. The muscle: fat
ratio of tissue, therefore, changes. A similar effect occurs in women triggered
by the menopause. Accumulated adipose under these circumstances is increasingly
difficult to MOBILIZE by exercise, and it contributes to the development
of diabetes, heart disease and hypertension.
The accompanying articles elaborate on the above issues and present several
new metabolic concepts. Read them before lecture; I will elaborate more
on these concepts at that time.
The genetic syndromes resulting in obesity are exceedingly rare and beyond
the scope of this discussion. The buffalo hump of the occasional patient
with Cushing's Disease and those receiving corticosteroid treatment for
immune medicated disease is well known to clinicians.
Questions?
Comments? Send a message to the CATS guru: jkessler@salus.uvm.edu
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