Anthropometry – quantitative measures of selected human landmarks.
Body composition – two-component model – the amount of fat and fat-free mass of which the body is composed. Fat-free mass is primarily composed of bone, muscle, vital organs, and connective tissue.
Four-component model – fat, protein, mineral, water
Why assess body composition?
- Suitable body composition is important for health.
- Establish reasonable fatness ranges for athletes in various sports
- Accurate measures of body composition are needed to develop sound weight reduction programs
- Knowledge of bone mineral content in women and children is important.
- Monitor changes in body composition associated with disease.
I. Essential Fat vs. Storage Fat
Essential fat – fat that is required for normal physiological functioning - structural components of cell membranes, required for the synthesis of certain hormones, transport of fat-soluble vitamins,etc.
Storage fat – fat that is stored in adipose tissue for energy supply purposes. It is located underneath the skin, in the abdominal cavity, and around certain organs.
II. Body Composition of Males vs Females
The average male is taller, heavier, has a larger muscle mass, and a lower total body fat content. For reference male and female, age 20 – 24:
Storage fat – female = 15% - male = 12%
Essential fat – female = 12% - male = 3%
Female has sex specific fat depots in the breasts, pelvic and thigh regions, and probably other areas.
“Male type” obesity – excess fat is deposited on the upper torso and around the abdomen. Male type obesity is associated with higher health risks.
“Female type” obesity – excess fat is deposited below the waist in the thighs, hips, and buttocks (ie) pear shape. After menopause females begin
depositing more fat in the abdominal area
The combination of diabetes and obesity is one of the largest epidemics the world has faced. The prevalence of overweight and obesity is increasing around the world and the obese are becoming more severely obese. In the past dozen years, scientists have discovered that adipose tissue is not simply a passive storehouse for fat, but an endocrine organ that secretes more than a dozen peptide and non-peptide compounds that trigger changes
throughout the body. When fat cells expand they release more of some of these compounds and less of others. Examples – leptin, adiponectin, inflammatory proteins, etc.
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Causes of the Obesity Epidemic
- Weight gain and obesity occur when energy intake exceeds energy expenditure – too much food and too little activity. For most of human history, survival meant avoiding starvation – our bodies are set up to deal with scarcity, not abundance.
- Decreased physical activity – auto-mobiles, increased crowding, crime patterns, technological advances and automation in the home and the workplace, many hours spent watching TV, playing video games, sitting
- at the computer
- Increased consumption of calories – consumption of large portion size meals, high-fat diets, high sugar intake
- Social environment – advertising, pressure to consume, influence of family and friends
- Biology – the epidemic of obesity is occurring on genetic backgrounds that have not changed, but it is now clear that genetics plays an important role in the development of obesity.
Data from overfeeding experiments with identical twins demonstrate that some individuals are more at risk than others to gain fat when energy intake surplus is maintained at the same level for everyone and when all
subjects are confined to a sedentary lifestyle.
NEAT – non-exercise activity thermogenesis. It is the energy expended by physical activities other than planned exercise – sitting, standing, walking, fidgeting, etc. In a recent research study, obese participants were
seated for 164 minutes longer per day than were lean participants.
6. Role of viruses? Do some viruses play a role in the expansion of adiposetissue mass? This is a new area of research.
IV. Common Techniques For Assessing Body Composition
Direct methods – chemical analysis of human cadavers Indirect methods – noninvasive techniques used on living persons
A. Height – Weight Tables
Desirable weight with regard to the lowest death rates is predicted from tables that have been developed by insurance actuaries.
- These tables do not consider body composition.
- Most of the data in the 1983 Metropolitan Life Insurance Height-Weight tables comes from white, middle-class, U.S. adults age 25 to 59 years. This is not a representative sample of the general North American population.
- No accepted method has been devised for determining frame size.
B. Body Density and Volume Measurements
Density = mass/volume. Body density will vary with the amount of body fat. Use underwater weighing or volumetry to measure body volume. In recent years the UWW technique has begun to be replaced by air- displacement
plethysmography (BOD POD method) where the subject is immersed not in water but in a closed air-filled chamber (plethysmograph). Measure the volume of air displaced inside the closed chamber. After body density has been determined using one of the above methods, use an equation, such as the equation developed by Siri, to determine percent body fat.
These equations make two basic assumptions:
- The human body has two compartments – fat and nonfat
- Each of these compartments has densities which are known constants.
Assume that fat has a density of 0.90 g/ml and nonfat a density of 1.10 g/ml.
For decades hydrostatic weighing has been used as a universal method for validating skinfold caliper formulae and all other methods (ie) it has been used as the “gold standard”.
Problems:- cadaver studies (Brussels cadaver study, 1984) have shown that the density of the nonfat compartment varies as a function of age, sex, and racial group. Therefore, a nonfat density value of 1.10 g/ml is not universally applicable. Conclusion – densitometry should not be used as a universal criterion for prediction of percent fat. Equations based on four component models are preferred over equations based on a two component model.
C. Weight – Height Indicies
Body Mass Index (BMI) – used as an indicator of obesity. This index uses the body mass (kg) divided by the height (meters) squared. Classification system for adults (20-70 years old):
BMI less than 18.5 = underweight
BMI of 25.0 to 29.9 = overweight
BMI of 30 or higher = obese
Recent research evidence indicates that these BMI cut-off points may need revision because the relationship between BMI and body composition, and between indices of fat distribution and the actual amount of visceral fat,
differs across ethnic groups. For example, Asian populations have a higher body fat percentage at a lower BMI compared to Caucasians. Change the definition for overweight for Asian populations from 25 to 23?
A 2007 study in Vancouver found that, for the same amount of total body fat, Chinese and South Asian people had a far greater concentration in their inner abdomen, where it poses the greatest risk for diabetes and heart disease. The main assumption of BMI guidelines is that BMI is closely associated with body fatness and consequent morbidity and mortality. However, some individuals who are overweight are not over-fat.
Criticism – BMI does not differentiate body composition.
BMI of NFL football players: Ray Lewis = 33, Nick Mangold = 36.6
BMI of NHL hockey players: Sidney Crosby = 27.8
Accumulating research evidence shows that waist circumference and/or waist-to-hip ratio is a better predictor of obesity related health risks than BMI. The prevalence of overweight and obesity amongst Canadian children and adults has increased significantly in the past 20 years.
D. Skinfold Measurements
Rationale – a relationship exists between the fat located in the depots directly beneath the skin and internal body fat and body density.
There are basically two ways to use fatfolds:
- Use the sum of a number of skinfolds as an indication of relative fatness among individuals. Also compare “before” and “after” in the same individual.
- Use fatfolds in conjunction with equations or tables to predict percent body fat.
Skinfold caliper formulae to predict percent fat are site and sample specific.
Assumptions in using skinfold measurements to predict percent fat:
- Constant densities in a two-compartment model
- Proper identification of measurement site and proper measurement technique
- Constant compressibility of the skinfold
- Fixed adipose tissue patterning
- Fixed proportion of internal to external fat
There are two types of body composition prediction equations:
- Population specific equations – developed from relatively small, homogeneous (age, sex, state of training, fatness) samples. Their application is limited to that subsample. Example – Sloan, Yuhasz
- Generalized equations – developed from large, heterogeneous samples.
These equations have a wider application in terms of age, and fatness. However, these equations should be used cautiously with unique populations such as extremely obese individuals and professional football players.
Example – Jackson and Pollock, Durnin & Womersley, Peterson, Wang
Even when the correct equation is used and the measurements are performed correctly, prediction of percent fat from skinfold measurements has an error of approximately 3-4 %.
E. Canadian Physical Activity, Fitness and Lifestyle Appraisal
This method requires the consideration of three different indicators for a comprehensive assessment of body weight, adiposity, and fat distribution.
- Body mass index – is the subject overweight?
- Sum of 5 skinfolds – triceps, biceps, subscapular, iliac crest, and medial calf. Is the subject over-fat?
- Waist girth – is the subject high in visceral adiposity – male type obesity?
F. O-Scale System
Adiposity rating, proportional weight rating, stanine scale
G. Bioelectrical Impedance Analysis
Electrical impedance units are used to measure the electrical resistance of the body. Impedance is greater in adipose tissue (14 – 22% water) than in bone and muscle (71 – 75% water). Attach electrodes to the subject. A low level electrical current (500 to 800 microamps at 50 kHz) is passed through the subject’s body. The higher the electrical resistance, the fatter the subject. The daily fluctuations in water content from exercise, dehydration, eating and drinking all need to be standardised to obtain optimum impedance results. Clients must adhere to strict pretest guidelines in order to yield valid estimates of their body composition.
The prediction equations that estimate fat free mass are validated using underwater weighing. These equations tend to overestimate fat mass in the lean and underestimate fat mass in the obese. Must use equations specific to given populations Error in percent fat estimation – approx. 3-5% body fat
H. Near-Infrared Interactance (NIR)
NIR is still in the developmental stages and there is much scepticism surrounding the use of NIR to assess body composition.
Principle – the degree of infrared light absorbed and reflected is related to the composition of the tissues. Optical densities are linearly related to subcutaneous and total body fat. The biceps is the best single site for estimating body fat using this method.
I. Other Procedures
- Dual energy X-ray absorptiometry – widely used for performing bone mineral density measurements
- Total body water – hydrometry
- Magnetic resonance imaging
- Computerized tomography
- Total body potassium
These laboratory methods are reasonably accurate but they are expensive, cumbersome and require highly trained technicians.
Conclusion – results of estimation of body composition should be interpreted cautiously.
V. Body Composition and Aging
Changes associated with aging in a prosperous, industrialized society:
- increased fat mass
- decreased muscle mass – sarcopenia
- decreased bone mass
These changes can be slowed down by a regular exercise program and proper dietary habits. Recent evidence indicates that skeletal fragility in elderly women is related to failure to obtain an optimal level of bone mass during childhood.
Co-morbidities/Complications Associated With Obesity
- Type II diabetes mellitus
- Coronary artery disease, and heart failure
- Higher incidence of certain cancers
- Higher levels of inflammatory markers in the body
- Sleep apnea
- Gallbladder disease
- Osteoarthritis of the weight-bearing joints
- Reduced fertility
- Impaired obstetric performance
- Reduced physical agility
- Co-morbidities/Complications Associated With Excessive Thinness
- Fluid-electrolyte imbalances
- Bone fractures
- Muscle wasting
- Cardiac arrythmias and sudden death
- Peripheral edema
- Renal disorders
- Reproductive disorders
The prevalence of anorexia nervosa is estimated at 0.5% of the population in the western industrialized countries. 90% of people with anorexia are female, with females between 15 and 19 years old making up 40% of all
cases. A 1990 study reported that the average bone mineral density of the spine of 18 to 27 year old anorexic women was equivalent to that of a 70 year old woman.
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