Lecture 2

Measurement of Obesity

Bonnie Beezhold, PhD, CHES

Assistant Professor, Nutrition

Benedictine University

Measurement of body mass Measurement of body mass index (BMI)index (BMI)

BMI correlates significantly with morbidity and mortality

BMI replaced Met Life height/weight tables and is now important for clinical standards and population comparisons

There is a good correlation between BMI and percent (%) body fat, but not in all ethnic groups

Measurement Units Formula and Calculation

Kilograms and meters (or centimeters) Formula: weight (kg) / [height (m)]2 With the metric system, the formula for BMI is weight in kilograms divided by height in meters squared. Since height is commonly measured in centimeters, divide height in centimeters by 100 to obtain height in meters.Example: Weight = 68 kg, Height =165 cm (1.65 m); 68 ÷ (1.65)2 = 24.98

Pounds and inches Formula: weight (lb) / [height (in)]2 x 703 Calculate BMI by dividing weight in pounds (lbs) by height in inches (in) squared and multiplying by a conversion factor of 703.Example: Weight = 150 lbs, Height = 5'5" (65")[150 ÷ (65)2] x 703 = 24.96

cdc.gov

BMI is the ratio of a person’s weight to the square of their height

May be an overestimate in people with high muscle mass (athletes and lactating women)

BMI has the same cut off points for males and females Women have the same relative risk but lower absolute risk

associated with overweight than men, thus women may tolerate body fat better than men

Interpretation of BMI

NHLBI Clinical Guidelines on the Identification, Evaluation and Treatment of Overweight and Obesity in Adults-the Evidence Report. Obesity Research 1998:(suppl.) 53S.

Measurement of obesity - body fat Measurement of obesity - body fat DistributionDistribution

People store body fat in two general ways, around the middle or around the hips/buttocks/upper legs

The “apple shape” fat distribution predicts levels of cardiovascular risk factors and disease Shape of most men and postmenopausal women

How to measure body fat distribution

Waist circumference and waist-to-hip ratio Waist circumference is the simplest and preferred way

Predicts intra-abdominal fat as accurately as WHR Correlates strongly with intra-abdominal adipose tissue as

assessed by a CT scan or MRI

Level 1 (alerting zone) Level 2 (action level)

Men ≥ 94 cm (~37”) ≥ 102 cm (~40”)

Women ≥ 80 cm (~32”) ≥ 88 cm (~35”)

Do WC values apply to all?

Ethnic-specific values for waist circumference(adapted from the IDF consensus worldwide

definition of the metabolic syndrome, available athttp://www.idf.org)

Country/Ethnic group Waist circumference

Europids (in USA, the ATPIII values Male 94 cmare likely to be used in clinical practice) Female 80 cm

South Asians Male 90 cmFemale 80 cm

Japanese Male 85 cmFemale 90 cm

East Mediterranean and Middle East Male, use European cut-offPopulation values until more specific data are available

Body compositionBody composition

Humans are assumed to have a body composition consisting of 80% lipid, 14% water, 5% protein, and <1% mineral

Most important consideration in evaluating body weight and composition is the proportion of total body weight that is fat (% body fat)

Body fat is the most variable constituent of the body; consists of essential fat and storage fat

Essential fat

Fat stored in bone marrow, heart, lungs, liver, spleen, kidneys, intestines, muscles, and lipid-rich tissues throughout the central nervous system

Required for normal physiological functions Reducing essential fat below some minimal amount

can impair overall health Extremes in dieting (and exercise) can reduce

essential fat stores

Storage fat (adipose tissue)

Located around internal organs (visceral fat) and directly beneath the skin (subcutaneous fat)

Provides bodily protection, serves as an insulator, energy reservoir

Level of adiposity, age, gender, heredity all play an important role in determining AT composition

Body composition changes over time

The relationship between subcutaneous fat and internal fat may not be the same for all individuals and may fluctuate during the life cycle. People get fatter when they get older even when their body weights are stable.

Body fat development

Three times in life we develop or form fat cells: 3rd trimester in utero first year of life puberty

Fat cells may change size, but they will not “burn off”…so, by exercising in the “fat burning” zone, we are actually reducing the size of fat cells

Most people, no matter the size, have around 75 billion fat cells

How much body fat is too much?

Too much body fat can have negative physiologic effects

Once men exceed 25% and women 32% fat, there is a dramatic correlation with illness and disease Dyslipidaemia, impaired heart function, heart disease

and hypertension, cancer, impaired immunity, gallbladder disease, kidney disease, insomnia/apnea, skin problems

Measurement of body Measurement of body compositioncomposition

Atomic, molecular, cellular, tissue, whole body levels Methods range from simple to complex with all having

limitations and some degree of error 2-component (2-C) model partitions body into fat mass

(FM) and fat-free mass (FFM) 3-C model partitions body into FFM, FM, and total body

water (TBW) 4-C model includes FM, TBW, and components of FFM

(minerals, total body protein)

The more components measured, the more difficult and costly the measurements are to perform, but fewer assumptions required.

Fat-free mass (FFM)

Devoid of all extractable fat; ‘dry’, containing mainly protein and minerals

Determinant of metabolic rate (BMR, RMR) Composed of metabolically active body mass

such as organs and muscle mass Brain, heart liver and kidney have greater rates

Also composed of supporting tissue such as bone and fluid

Laboratory methods: most common are 2-C methods of densitometry and hydrometry

Field methods: most common are skinfold thickness and bio-impedance analysis (BIA)

Methods are often used with prediction equations to estimate components at the other four body composition levels

Whole body measurement (level V)

Triceps:•Vertical fold •Posterior midline of the upper arm •Halfway between acromion (shoulder) and olecranon processes (elbow) •Arm held freely to side of body

Subscapula:•Diagonal fold •1 to 2 cm below the inferior angle of the scapula

Suprailiac:•Diagonal fold •Anterior axillary line (modern technique)

•immediately superior to iliac crest •in line with natural angle of iliac crest

•Mid-axillary line (traditional technique)

•Superior to iliac crest

Usually the subscapular and triceps are measured

Energy balanceEnergy balance

Energy intake – equal to the energy liberated during the oxidation of food

Energy expenditure – includes the energy: immediately lost as heat (thermogenesis) used to do work (driven by ATP) stored in C-C and C-H bonds and…

In liver and muscles as glycogen In adipose tissue as triglycerides In body protein (~50% available for energy if needed)

Types of thermogenesis

Isothermic thermogenesis: due to changes in muscle tone without any work done

Dynamic thermogenesis: from stretched muscle without any work

Psychological thermogenesis: anxiety, stress stimulate epinephrine secretion

Cold-induced thermogenesis: thermal regulation; shivering vs non-shivering

Diet-induced thermogenesis: following a meal Drug-induced thermogenesis: caffeine (60-80mg raises

BMR 5-10% over 1-2 hrs), nicotine, alcohol

Miller ,1982

Components of Daily Energy Expenditure

Segal KR et al. Am J Clin Nutr. 1984;40:995-1000.

Alternative compartmentalization of energy expenditure

Based on resting and non-resting metabolic rate

Involuntary activity (fidgeting) is always referred to as non-exercise activity thermogenesis (NEAT)

)

Dulloo & Jacquet, 2003

Estimating energy requirements (kilocalories)

Energy requirements are related to energy expenditure (EE) which depends on body size and composition

Assessing body composition vs just body weight is more accurate to find true requirements, however, body composition varies

Estimates of energy requirements are based on BMR multiplied by a PA factor

Accuracy of estimate would be improved by using FFM, but assessing FFM is not available on a population level

Metabolic rate

Basal metabolic rate (BMR) reflects the energy required to perform the most essential activities Largest determinant is body size (particularly FFM); rate declines by

1-2% per decade between ages 20-70 (declining FFM)

Resting metabolic rate (RMR) reflects resting energy expenditure (REE) occurring during normal cellular and organ functions

Total metabolic rate (TMR) is the total rate of kilocalorie consumption to fuel all ongoing activities

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How do we measure metabolic rate?

Direct calorimetry - measurement of the amount of heat produced by a subject enclosed within a small chamber - most accurate

Indirect calorimetry - measures gas exchange after resting - accurate to within 5%

http://www.letmedical.com/products

Mifflin's equation - estimates RMR to within 10% of that measured (Frankenfield et al, 2005)

Harris-Benedict equation - most widely used

Cunningham's equation - more appropriate for athletes

How do we estimate RMR?

Predictive equations are population specific

http://www.exercisebiology.com/

Energy Metabolism in Lean and Obese Subjects

Energy expenditure due to Physical Activity

Amount expended depends on type, intensity, frequency of PA

Contribution: 10-15% Measurement: characterized at different levels of

effort based on the standard of a metabolic equivalent (MET), the unit used to estimate the amount of oxygen used by the body during PA (Ainsworth et al., 1993) 

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Discrepancy Between Reported and Actual Energy Intake and Expenditure