HUN1201 Exam 3

Body Weight Includes:

• Fat, muscle, fluid, all tissues

• Water = 60% adult’s body weight

How many kcal is 1lb of body fat?

3500-3600 kcal

Energy Balance =

Caloric intake - energy expenditure

How to measure food energy

Bomb calorimeter - food is burned and it’s energy is released as heat, that heat energy is measured in kcal

Basal Metabolic Rate can change with

change in muscle in the body and exercise

Appetite

• food intake regulation

• integrated response to sight, smell, thought, or taste of food that initiates or delays eating

• psychological

• prompts a person to eat

Hunger

• food intake regulation

• physiological response to nerve signals and chemical messengers

• hypothalamus is responsible for hunger

• influenced by absence of nutrients in bloodstream

Satiation

• food intake regulation

• short term signal to stop eating

• occurs when food enters GI tract and hunger diminishes

• fullness: condition of being filled to capacity

• Protein is the most satiating and high fiber foods fill you up

Satiety

• food intake regulation

• long term signal to not start eating again

• after a meal, this continues to suppress hunger

• Fat produces these signals strongly once it enters the intestine

Total Energy Expenditure (TEE) =

thermic effect of a meal + physical activity + BMR

Thermic Effect of a Meal

1. energy expended to digest and absorb food

2. varies with composition of a meal

3. very small % of total energy

Physical Activity

All activity in the day

Basal Metabolic Rate

• energy expended to carry out essential body functions

• thermogenesis, biochemical reactions, heart, brain, kidneys, etc.

Thermogenesis

The biological process of heat production in organisms to help maintain a stable core body temperature

BMR varies depending on

• lean body mass

• hormones

• stress

• genetics

When can men on average eat more?

Muscle is more metabolically active than fat and men typically have more lean body mass than women

To measure BMR via gas exchange

• awake

• laying down

• 12 hr post prandial (after a meal)

• comfortable room temperature

Factors that affect BMR

Age, height, growth, body composition, fever/stresses, environmental temperature, fasting/starvation/malnutrition, hormones, smoking/caffeine, sleep

Age effect on BMR

lean body mass diminishes with age, slowing the BMR

Height effect on BMR

in tall, thin people, the BMR is higher

Growth effect on BMR

In children, adolescents, and pregnant people the BMR is higher

Body Composition effect on BMR

The more lean tissue, the higher the BMR; the more fat tissue, the lower the BMR

Fever/Stresses effect on BMR

Both raise the BMR

Environmental Temperature effect on BMR

Both heat and cold raise the BMR

Fasting/Starvation/Malnutrition effect on BMR

All lower the BMR

Hormones effect on BMR

The thyroid hormone thyroxine can speed up or slow down the BMR

Smoking/Caffeine effect on BMR

Speeds up energy expenditure

Sleep effect on BMR

BMR is lowest during this time

Equations to measure BMR

Harris-Benedict Equation, Mifflin St. Jeor

Weight Gain

• change in weight

• safe rate of gain dependent on state of individual

Weight Loss

• change in weight

• safe rate of weight loss

  • not more than 1-2lbs/week

  • fat not muscle or dehydration

  • should be sustainable

Reduce Calories in Diet

• change in weight

• factors that influence eating can override satiety

Factors that influence eating

• stress

• time of day

• availability of food

• smell, sight, taste of food

• environment

Increase Physical Activity

• change in weight

• increases metabolic rate

• increases lean body mass while decreasing fat mass

What is a healthy body weight?

• Body mass index (BMI): doesn’t indicate body composition

• % body fat

• In general, women have ~12% more body fat than men at the same BMI

Ways to measure body tissues

• Skinfold measures

• Hydrodensitometry

• Bioelectrical impedance

• Waist Circumference

• Dual-energy X-ray absorptiometry (DEXA)

• Air-displacement plethysmography (Bod Pod)

Skinfold Measures

Estimate body fat by using a caliper to gauge the thickness of a fold of skin on the back of the arm, below the shoulder blade, and other places, and then comparing these measurements with standards

Hydrodensitometry

Measures body density by weighing the person first on land and then while submerged in water. The difference between the persons actual weight and underwater weight provides a measure of the body’s volume. A mathematical equation using the 2 measurements determines body density, which gives us an estimation of body fat %.

Bioelectrical Impedance

Measures body ft by using a low-intensity electrical current. Because electrolyte-containing fluids, which readily conduct an electrical current, are found primarily in lean body tissues, the leaner the person, the less resistance to the current. The measurement of electrical resistance is then used to estimate body fat %.

Waist Circumference

Measures central obesity by placing a nonstretchable measuring tape around the waist just above the bony crest of the hip. The tape runs parallel to the floor and is snug, but does not compress the skin.

Dual-energy X-ray Absorptiometry (DEXA)

Uses 2 low-dose X-rays that differentiate among fat-free soft tissue (lean body mass), fat tissue, and bone tissue, providing a precise measurement of total fat and its distribution in all but extremely obese subjects.

Air-Displacement Plethysmography (Bod Pod)

Estimates body composition by having a person sit inside a chamber while computerized sensors determine the amount of air displaced by the person’s body.