Body Weight and Composition
What is ideal body weight?
n
A body
weight that is “healthy”
n
Guided by
body mass index (Quetelet’s Index)
Body weight in kilograms
(Height in meters)2
n
BMI of
18.5 to 25 is considered normal
n
A low BMI
(<18.5) may be associated with malnutrition or serious disease
n
A high BMI
(25-30) is indicative of overweight; increased risk for health problems
n
A very
high BMI (>30) is indicative of obesity, more than 20% over healthy body
weight; great risk to health
Composition of the Body
n
4 Components
n
Total body fat (density of
0.9 g/cc3)
n
Fat-free mass (density of
1.1 g/cc3)
n
Bone mineral (density of
1.3-1.4 g/cc3)
n
Body water (density of 1.0
g/ml)
n
Overall body density of
body ~ 1.02 – 1.10
n
The higher the density the
lesser the % body fat
The Body Composition Components
n
Total Body Fat
n
Essential – necessary
for proper functioning of brain, nerve tissue, bone marrow, heart tissue, and
cell membranes
n
Males – 3%
essential fat
n
Females – 12-15%
essential fat
n
Storage – depot of
excess energy
n
Approximately 50% of fat
is subcutaneous fat
n
Dimpled, quilt-like skin
surface is sometimes noted as cellulite [fat + glycoproteins (attracts water)]
n
Other fat, deep in core of
body is visceral fat
The Body Composition Components
n
Fat-free Mass
n
Accounts for protein and
water (+ small amount of minerals and glycogen)
n
Hence, skeletal muscle,
heart, and organs
n
Sometimes defined as lean
body mass
n
However, this term
includes essential body fat
The Body Composition Components
n
Bone Mineral
n
Consists of 50% water, 50%
solid matter (protein and minerals)
n
Accounts for 12-15% of
total body weight
The Body Composition Components
n
Body Water
n
60% of average adult
weight is water
n
Of this, fat-free mass is
70% water
n
Of this, adipose tissue is
10% water
Ratings of Body Fat % for Males
and Females (18-30 years)
Waist-Hip Ratio and Risk
How does body control weight?
How does body control weight?
n
Energy Intake
n
Appetite regulation
n
Influenced by appetite
centers in hypothalamus
n
Hunger control center
n
Stimulates eating behavior
e.g. seeing
something you like to eat
n
Satiety control center
n
When stimulated, inhibits
hunger center
e.g. stomach
fullness stimulates stretch receptors
n
Temperature control center
n
Increase in body
temperature inhibits appetite
How does body control weight?
n
Energy
Intake
n
Nutrient
regulation
n
Receptors
in hypothalamus, liver, & other areas sense appearance of different
nutrients
n
Glucostatic
Theory
n
Food
intake is related to levels of blood glucose
-
high levels - ↓ intake;
low levels - ↑ intake
n
Lipostatic
Theory
n
Food
intake is related to levels of fats in blood
-
high levels - ↓ intake;
low levels - ↑ intake
n
Aminostatic
Theory
n
Food
intake is related to levels of protein in blood
-
high levels - ↓ intake;
low levels - ↑ intake
How does body control weight?
n
Energy Expenditure
n
Majority of energy
expended by body on a daily basis is due to basal (or resting) energy
expediture; other portion by physical activity
n
Components
n
Brown fat – comprises ~
1% of body fat but has high energy turnover (release heat without ATP
production)
n
Account for nonshivering
thermogenesis
n
Found in neck, back and
chest areas
n
White fat – majority
type of fat in body
n
Source of energy with some
nonshivering thermogenesis
n
Hormones – from thyroid and adrenal glands help control
expenditures
How does body control weight?
n
Feedback Controls of
Energy Balance
n
Short-term
n
Stomach size, neural and
hormonal inputs, and nutrient inputs
n
Long-term
n
Set-point Theory (control
in hypothalamus)
n
Body is programmed to a
certain weight
Feedback Control of
Energy Balance
n
Long-term
n
Set-point Theory
n
One possible mechanism – action of
leptin
n
Hormone derived from body
fat
- the more fat
you have, the more leptin you
produce; less fat, lesser leptin produced
- inhibits
action of NPY in hypothalamus
- NPY is a stimulant to food intake and
reduces
energy expenditure
n
Hence
- In normal
situations, the greater the body fat, the lesser the stimulus to gain weight
and greater sense of increasing energy expenditure
Feedback Control of
Energy Balance
n
Long-term
n
Activity-stat Theory
n
Proposed center in brain
that functions as a set-point to increase or decrease physical activity
What is cause of obesity?
n
Generally, a greater
caloric intake in comparison to energy expenditure
n
Causal factors
n
Genetics
n
Inheritability of obesity
approximates 25-40%
n
Possibility that there are
fewer receptors in hypothalamus to recognize lepin levels
n
Lack of uncoupling
proteins (UCP’s)
- responsible
for activating thermogenesis in brown and white fat
n
Thrifty gene
- suggested
that there is a gene that allows obese individuals to conserve more energy
n
Impaired metabolic
functions
What is cause of obesity?
n
Causal factors
n
Environment
n
Alcohol consumption
n
Does not suppress appetite
nor fat intake
n
Nicotine (in cigarettes)
n
Tends to inhibit appetite
and increase resting energy expenditure
- smokers who
quit tend to gain significant weight within a 2 year period
n
Some teenagers who are
concerned about weight control and dieting start smoking
What is cause of obesity?
n
Causal factors
n
Environment
n
Dietary fat
n
Highly palatable
n
Contains more calories per
gram than CHO & protein
n
Body’s appetite
centers respond more slowly to fat than CHO and protein
n
Stored more efficiently
than CHO and protein
n
High dietary fat intake
leads to leptin resistance in hypothalamus
n
Excess calorie intake
n
Fat-free and low-fat foods
suggest to many that more food can be consumed without extra gain in weight
What is cause of obesity?
n
Causal factors
n
Environment
n
Physical inactivity
n
Technological advances of
daily living have made an impact on the level of physical activity that we are
inclined to participate in
Summary
n
Major cause for “modern” obesity is
environmental influence; rapid increase can’t be due to genetics
n
Primarily increased
consumption of fat calories and decreased level of physical activity
n
Settling-point theory
n
Set point may be modified
depending on flexibility of our genes and their interaction with environment
How is fat deposited in body?
n
Fat
deposition
n
Hyperplasia
n
Increase
in number of fat cells
n
Originally
believed to occur only during early years of life
n
Recent
information suggests that more fat cells will be formed when existing fat cells
reach their size capacity
n
Hypertrophy
n
Increase
in size of fat cell
n
Believed
to be associated with adult obesity
n
Existing
fat cells have maximum potential size of 1 microgram of fat per cell
n
Note:
once fat cell is formed, it doesn’t
disappear with weight loss, it just gets smaller
How is fat deposited in body?
n
Regional Fat
n
Android (male)-type
obesity
n
Characterized as
accumulation of fat in the abdominal region; “apple-shape”
n
Greater health risk since
fat cells in this region are larger and highly metabolically active
n
Release free fatty acids
into blood and thus contribute to abnormalities in glucose and fat metabolism
n
Associated with Metabolic
Syndrome (Syndrome X)
n
Symptoms include high
insulin levels, impaired glucose function, bad cholesterol profile, & blood
clotting problems
How is fat deposited in body?
n
Regional Fat
n
Gynoid (female)-type
obesity
n
Characterized as
accumulation of fat in the gluteal-femoral region (i.e. hips, thighs,
buttocks); “pear-shape”
n
Less health risk since fat
cells in this region tend to store and lose fat less readily
n
Less resistant to let its
fat go so more difficult to lose fat in these body areas
n
Diet and exercise programs
will preferentially result in more fat
loss in abdominal region than gluteal-femoral area
Obesity Risks in Children
n
Obesity
is becoming a major health risk in children
n
Approximately
15% of children in U.S. are overweight & an additional 15% are at risk of
becoming overweight
n
Incidence
of Type 2 diabetes is rising, along with other coronary heart disease risks
n
This is
likely to carry over to adulthood
n
Psychosocial
problems are also on the rise
n
Several
organizations have been instituted to deal with the problem of obesity; one in
particular is AFHK
n
Action
for Healthy Kids (AFHK) is a nationwide initiative dedicated to improving the
health and educational performance of children through better nutrition and
physical activity in schools.
Health Problems with Improper
Weight Loss
n
Dehydration
n
Induced
by exercise, exposure to heat, and use of diuretics and laxatives
n
Resulting
in water and electrolyte imbalances causing heart and kidney damage
n
Poor
outcomes from weight-loss drugs
n
Drug
types
n
Adrenergic
drugs – suppress
appetite & ↑ resting
energy expenditure
n
Amphetamines,
ephedrine, phentermine
n
Serotonin
agents – suppress
appetite
n
Fluoxetine
(Prozac) – also an
antidepressant
n
Combined
agents
n
Long-term
use can result in seizures, psychoses, ECG abnormalities, lung problems,
addiction, and death
Health Problems with Improper
Weight Loss
n
Weight
Cycling (yo-yo syndrome)
n
Chronic
dieting characterized by intervals of high calorie diet and very low calorie
diets (VLCD)
n
Early
studies suggested that VLCD resulted in decreased thermic effect of food,
decreased resting energy expenditure, and enhanced food efficiency (less
wasted; hence more stored)
n
More
weight put back when eating high calorie diet since body is remembering to
conserve and store energy
n
More
recent research suggests that weight cycling may not have adverse body
composition or health effects, as long as weight regain does not exceed weight
lost
n
This
issue is still open for debate
Health Problems with Improper
Weight Loss
n
Young athletes and
children
n
Caloric restriction in
young children may hamper growth due to lack of essential nutrients
n
Growth rate compared in
adolescent female gymnasts and swimmers
n
Growth rate velocity was
less in gymnasts
n
Possibly due to heavy
training (> 18 hrs/wk)
n
Also possibly due to
metabolic effects of dieting
- inhibition
of hypothalamus and pituitary gland function