Body Weight and Composition

What is ideal body weight?

n            A body weight that is healthy

n           Guided by body mass index (Quetelets 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 (UCPs)
- 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   Bodys 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 cant 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 doesnt 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