Do body fat analyzers really work?
- Thread starter Nobody
- Start date
NOpe, it's not takign your pulse, it's running a mild current through your body to see how much you resist the current, and that's how it determines body fat. Just like a Tanita scale.
However if you're full of sodium, it'll be way off. If you're dehydrated, it'll be way off. If you're underhydrated, it'll be off. If you're perfectly hydrated, it might only be off by +/- 1.0%
Hence, kinda useless for 'real' bodyfat tracking.
However if you're full of sodium, it'll be way off. If you're dehydrated, it'll be way off. If you're underhydrated, it'll be off. If you're perfectly hydrated, it might only be off by +/- 1.0%
Hence, kinda useless for 'real' bodyfat tracking.
FYI... I have been tracking between 22-23% BF on my Tanita every morning for three weeks. I just got my BF tested by a physician and got a 17.1% BF reading. So no, they are not that accurate. Though the models that also test water % may give you a better reading after you do the math.
INTERESTING ...
A variety of methods are used to determine body composition. Techniques such as dual X-ray absorptiometry (DEXA), magnetic resonance imaging (MRI), and underwater weighing are just a few. Underwater weighing is considered the "gold standard" in body fat measurement. The accuracy of other methods is determined by comparing them to underwater weighing.
Body fat percentages are regularly measured at fitness and wellness centers. Since high-tech procedures are expensive and time consuming, more practical methods are used. The most common methods to determine body fat include skinfold techniques, girth measurements and bioelectrical impedance analysis (BIA).
It is important to remember all techniques currently used are estimates, and are prone to error. BIA and skinfold measurements have a standard error of about 3%. Therefore, if results of an analysis indicate you have 17% body fat, your body fat ranges between 14 and 20%. There's even a small chance the error range may be greater than 3%. Even underwater weighing has a standard error of 2%. Body composition measurement is not an exact science.
Bioelectrical Impedance Analysis
During BIA, electrodes are placed on the hand and foot, and an individual is hooked up to a machine. The device sends a weak, painless electrical current through the body. Although many people think BIA measures body fat, it really determines the ability of body tissues to conduct electricity. The technique is based upon the principle fat tissue is a less effective conductor of electricity than lean tissue. The faster the current passes through the body, the leaner the individual. Results from BIA provide an estimate of total body water. Using values of total body water, lean body mass and body fat can be calculated using mathematical equations.
The National Institutes of Health have stated BIA provides a good estimate of body composition. However, BIA values are affected by a number of variables that must be standardized if measurements are going to be accurate. The variables include electrode placement, body position, dehydration, exercise and ambient temperature. These factors are usually tightly controlled during research studies, but are often disregarded in fitness centers which makes the estimate of body fat less accurate. The following guidelines are recommended for BIA.
1. Place electrodes according to manufacturer specifications (sites should be measured). Misplacing the electrode by as little as one centimeter decreases measurement accuracy.
2. Body position affects BIA. The test is most accurately done in the supine position. Limbs should not be crossed.
3. No eating or drinking within four hours of the test.
4. No exercise within 12 hours of the test. 5. No alcohol consumption within 48 hours of the test.
6. No diuretics within seven days of the test.
7. Urinate within 30 minutes of the test.
Skinfold Measurements
Assessing body composition using skinfold thickness is based on the principle that approximately half the body's fatty tissue is directly beneath the skin. The skinfold test is done with the aid of calipers. Several sites must be measured to determine total fat percentage.
Training and practice are essential in obtaining accurate skinfold measurements. Even with adequate practice, varied measurements are found among different technicians, calipers and protocols. In a study by Timothy Lohman, M.D., four experienced investigators were told to follow the same skinfold procedures. However, they did not train together to confirm the same measurement technique was used. Each investigator measured the same subjects using two different kinds of calipers and protocols. Three important points emerged--body fat percentage was affected by the protocol used, the type of skinfold caliper used affected the measurement of body fat, and there were variations in the measurement of skinfold sites among the different investigators.
This does not suggest skinfold measurements are not accurate or useful. A recent study by scientists at Creighton University compared the accuracy of measuring body fat percentage with skinfold calipers, near-infrared interactance and BIA in women ages 17 to 29. All measurements were compared to underwater weighing. The results of this study indicated skinfold measurements most accurately estimated the percentage of body fat for this population, and therefore were recommended over the BIA and near-infrared procedures.
In order to obtain the most accurate skinfold measurements, they should always be performed by the same technician. Also, the same protocol and calipers should always be used. Follow the selected protocol exactly, and do not measure skinfolds after exercise because the shift in body fluid to the skin tends to increase the size of the skinfolds. If you are new at measuring skinfolds, practice at least 100 times.
For a thorough review on skinfold technique and a description of skinfold sites, refer to Advanced Fitness Assessment & Exercise Prescription (Human Kinetics, $40) by Vivian H. Heyward.
Following the measurement of skinfolds, it is not necessary to predict the percentage of body fat. Simply keep a sum of skinfold thicknesses from selected body sites. If the sum of skinfold thicknesses is decreasing, so is the percentage of body fat.
Special Considerations
BIA and skinfold measurements rely on population specific mathematical equations. This means the analysis can be applied only to people with similar characteristics such as age and gender. The equations suit most people. However, there are special groups of individuals for whom prediction of body fat is not reliable. BIA and skinfold measurements overestimate the percentage of body fat in lean subjects and underestimate it in obese subjects. Both of these techniques are extremely unreliable when used to measure the obese.
Extreme muscular hypertrophy presents special problems that may limit the accuracy of body composition assessment. A recent study by Loren Cordain at Colorado State University found inconsistencies among commonly used procedures for estimating body fat percentages in competitive male body builders. The average percentage of body fat for the body builders was 16.7% for BIA, 12.5% for underwater weighing and 10.4% for skinfolds. BIA overestimated the body fat percentage because equations for men who did not weight train were applied to highly muscled athletes.
I guess I got my question answered
A variety of methods are used to determine body composition. Techniques such as dual X-ray absorptiometry (DEXA), magnetic resonance imaging (MRI), and underwater weighing are just a few. Underwater weighing is considered the "gold standard" in body fat measurement. The accuracy of other methods is determined by comparing them to underwater weighing.
Body fat percentages are regularly measured at fitness and wellness centers. Since high-tech procedures are expensive and time consuming, more practical methods are used. The most common methods to determine body fat include skinfold techniques, girth measurements and bioelectrical impedance analysis (BIA).
It is important to remember all techniques currently used are estimates, and are prone to error. BIA and skinfold measurements have a standard error of about 3%. Therefore, if results of an analysis indicate you have 17% body fat, your body fat ranges between 14 and 20%. There's even a small chance the error range may be greater than 3%. Even underwater weighing has a standard error of 2%. Body composition measurement is not an exact science.
Bioelectrical Impedance Analysis
During BIA, electrodes are placed on the hand and foot, and an individual is hooked up to a machine. The device sends a weak, painless electrical current through the body. Although many people think BIA measures body fat, it really determines the ability of body tissues to conduct electricity. The technique is based upon the principle fat tissue is a less effective conductor of electricity than lean tissue. The faster the current passes through the body, the leaner the individual. Results from BIA provide an estimate of total body water. Using values of total body water, lean body mass and body fat can be calculated using mathematical equations.
The National Institutes of Health have stated BIA provides a good estimate of body composition. However, BIA values are affected by a number of variables that must be standardized if measurements are going to be accurate. The variables include electrode placement, body position, dehydration, exercise and ambient temperature. These factors are usually tightly controlled during research studies, but are often disregarded in fitness centers which makes the estimate of body fat less accurate. The following guidelines are recommended for BIA.
1. Place electrodes according to manufacturer specifications (sites should be measured). Misplacing the electrode by as little as one centimeter decreases measurement accuracy.
2. Body position affects BIA. The test is most accurately done in the supine position. Limbs should not be crossed.
3. No eating or drinking within four hours of the test.
4. No exercise within 12 hours of the test. 5. No alcohol consumption within 48 hours of the test.
6. No diuretics within seven days of the test.
7. Urinate within 30 minutes of the test.
Skinfold Measurements
Assessing body composition using skinfold thickness is based on the principle that approximately half the body's fatty tissue is directly beneath the skin. The skinfold test is done with the aid of calipers. Several sites must be measured to determine total fat percentage.
Training and practice are essential in obtaining accurate skinfold measurements. Even with adequate practice, varied measurements are found among different technicians, calipers and protocols. In a study by Timothy Lohman, M.D., four experienced investigators were told to follow the same skinfold procedures. However, they did not train together to confirm the same measurement technique was used. Each investigator measured the same subjects using two different kinds of calipers and protocols. Three important points emerged--body fat percentage was affected by the protocol used, the type of skinfold caliper used affected the measurement of body fat, and there were variations in the measurement of skinfold sites among the different investigators.
This does not suggest skinfold measurements are not accurate or useful. A recent study by scientists at Creighton University compared the accuracy of measuring body fat percentage with skinfold calipers, near-infrared interactance and BIA in women ages 17 to 29. All measurements were compared to underwater weighing. The results of this study indicated skinfold measurements most accurately estimated the percentage of body fat for this population, and therefore were recommended over the BIA and near-infrared procedures.
In order to obtain the most accurate skinfold measurements, they should always be performed by the same technician. Also, the same protocol and calipers should always be used. Follow the selected protocol exactly, and do not measure skinfolds after exercise because the shift in body fluid to the skin tends to increase the size of the skinfolds. If you are new at measuring skinfolds, practice at least 100 times.
For a thorough review on skinfold technique and a description of skinfold sites, refer to Advanced Fitness Assessment & Exercise Prescription (Human Kinetics, $40) by Vivian H. Heyward.
Following the measurement of skinfolds, it is not necessary to predict the percentage of body fat. Simply keep a sum of skinfold thicknesses from selected body sites. If the sum of skinfold thicknesses is decreasing, so is the percentage of body fat.
Special Considerations
BIA and skinfold measurements rely on population specific mathematical equations. This means the analysis can be applied only to people with similar characteristics such as age and gender. The equations suit most people. However, there are special groups of individuals for whom prediction of body fat is not reliable. BIA and skinfold measurements overestimate the percentage of body fat in lean subjects and underestimate it in obese subjects. Both of these techniques are extremely unreliable when used to measure the obese.
Extreme muscular hypertrophy presents special problems that may limit the accuracy of body composition assessment. A recent study by Loren Cordain at Colorado State University found inconsistencies among commonly used procedures for estimating body fat percentages in competitive male body builders. The average percentage of body fat for the body builders was 16.7% for BIA, 12.5% for underwater weighing and 10.4% for skinfolds. BIA overestimated the body fat percentage because equations for men who did not weight train were applied to highly muscled athletes.
I guess I got my question answered
Anthropometric Measurements
Anthropometry includes measures such as height, weight and circumferences of various body segments. One of the biggest advantages of circumference measurements is they are easily understood by clients, and even small improvements are usually motivating. Circumference measurements can be used to estimate body composition, although results are not accurate. Anthropometric measurements also provide a quick, easy way to give clients information about their health and wellness.
Scientific evidence suggests the way people store fat affects their disease risk. Individuals with large amounts of abdominal fat (apple shaped) are at higher risk for heart disease, congestive heart failure, high blood pressure, Type II diabetes, and strokes than people with similar amounts of fat stored in the hips and thighs (pear shaped). A waist-to-hip ratio test (the circumference of the waist divided by the circumference of the hips) measures the narrowest part of the torso and the point of greatest circumference around the buttocks region. Men should probably lose weight if the waist-to-hip ratio is 1.0 or higher, and women should probably lose weight if the ratio is .85 or higher.
Another approach, the Body Mass Index (BMI), looks at the relationship of weight to height. Since the BMI method uses the metric system, determination of body weight in kilograms and height in meters is required. The formula for finding BMI is as follows.
BMI = Body weight in kilograms/(Height in meters) 2
Multiply body weight in pounds by 0.454 for weight in kilograms. Multiplying height in inches by 0.0254 will give you height in meters. For example, if a man weighs 200 pounds and is 6'1" (73 inches) tall:
Weight in kilograms:
200 x 0.454 = 90.8 Height in meters: 73 x 0.0254 = 1.854
90.8 = 90.8 = 26.4 [(1.854).sup.2] 3.437
BMI values above 25 are associated with an increased rate of obesity-related health problems such as high blood pressure and coronary heart disease. The American Dietetic Association classifies individuals with a BMI greater than 30 as obese, and those with a BMI greater than 40 as morbidly obese and in need of prompt medical attention.
Future Trends
A new method for estimating body fat, the BOD POD Body Composition System, works on the principle of air displacement, as opposed to underwater weighing which works on the principle of water displacement. Subjects sit in an egg-shaped fiberglass chamber (remember "Mork from Ork?") that contains a weighing device and computer used to determine body density. Although only a couple of studies have been completed, the BOD POD looks promising as a valid method to determine body composition. This new method has several advantages over underwater weighing. It is quick (three to five minutes), relatively simple to operate and requires little effort by the subject.
Since all body composition measurements are indirect because they measure fat inside the body from the outside, even the most sophisticated techniques are not perfect. It is important to help clients keep the results of body fat analyses in perspective. Clients often become alarmed if their body fat percentage increases by as little as half a percent, but this is within the range of measurement error. It is likely a small increase such as this is a result of changes in measurement technique rather than a true increase in body fat.
RELATED ARTICLE: Techniques Used to Determine Body Fat Percentage
Measurement Technique Component Measured Anthropometry Measures body segment circumferences.
Bioelectrical Impedance Analysis Measures resistance to electric current (BIA) passed through the body. Predicts body
water content, lean body mass, and body
fat.
Dual energy X-ray absorptiometry X-ray technique at two energy levels. (DEXA) Used to image body fat or calculate bone
mass.
Infrared Interactance Infrared light passes through tissues.
Magnetic Resonance Imaging Magnetic field and radio-frequency waves (MRI) similar to CAT scan. Useful for measuring
deep abdominal fat.
Skinfold Thickness Measures subcutaneous fat folds.
Underwater Weighing Full body submersion to measure water
displacement. Predicts body density, body
fat and lean body mass.
Disease Risk
According to
Waist-to-Hip Ratio
[TABULAR DATA OMITTED]
Disease Risk
According to Body
Mass Index
BMI Disease Risk
20.00-24.99 Very low
25.00-29.99 Low
30.00-34.99 Moderate
35.00-39.99 High
[greater than or equal to]40.00 Very high
Deborah Riebe, Ph.D., is an assistant professor in the Department of Physical Education and Exercise Science at the University of Rhode Island. Ronan Hingerty, B.S., is a graduate student in exercise science at the University of Rhode Island.
COPYRIGHT 1996 Aerobics and Fitness Association of America
COPYRIGHT 2004 Gale Group
Anthropometry includes measures such as height, weight and circumferences of various body segments. One of the biggest advantages of circumference measurements is they are easily understood by clients, and even small improvements are usually motivating. Circumference measurements can be used to estimate body composition, although results are not accurate. Anthropometric measurements also provide a quick, easy way to give clients information about their health and wellness.
Scientific evidence suggests the way people store fat affects their disease risk. Individuals with large amounts of abdominal fat (apple shaped) are at higher risk for heart disease, congestive heart failure, high blood pressure, Type II diabetes, and strokes than people with similar amounts of fat stored in the hips and thighs (pear shaped). A waist-to-hip ratio test (the circumference of the waist divided by the circumference of the hips) measures the narrowest part of the torso and the point of greatest circumference around the buttocks region. Men should probably lose weight if the waist-to-hip ratio is 1.0 or higher, and women should probably lose weight if the ratio is .85 or higher.
Another approach, the Body Mass Index (BMI), looks at the relationship of weight to height. Since the BMI method uses the metric system, determination of body weight in kilograms and height in meters is required. The formula for finding BMI is as follows.
BMI = Body weight in kilograms/(Height in meters) 2
Multiply body weight in pounds by 0.454 for weight in kilograms. Multiplying height in inches by 0.0254 will give you height in meters. For example, if a man weighs 200 pounds and is 6'1" (73 inches) tall:
Weight in kilograms:
200 x 0.454 = 90.8 Height in meters: 73 x 0.0254 = 1.854
90.8 = 90.8 = 26.4 [(1.854).sup.2] 3.437
BMI values above 25 are associated with an increased rate of obesity-related health problems such as high blood pressure and coronary heart disease. The American Dietetic Association classifies individuals with a BMI greater than 30 as obese, and those with a BMI greater than 40 as morbidly obese and in need of prompt medical attention.
Future Trends
A new method for estimating body fat, the BOD POD Body Composition System, works on the principle of air displacement, as opposed to underwater weighing which works on the principle of water displacement. Subjects sit in an egg-shaped fiberglass chamber (remember "Mork from Ork?") that contains a weighing device and computer used to determine body density. Although only a couple of studies have been completed, the BOD POD looks promising as a valid method to determine body composition. This new method has several advantages over underwater weighing. It is quick (three to five minutes), relatively simple to operate and requires little effort by the subject.
Since all body composition measurements are indirect because they measure fat inside the body from the outside, even the most sophisticated techniques are not perfect. It is important to help clients keep the results of body fat analyses in perspective. Clients often become alarmed if their body fat percentage increases by as little as half a percent, but this is within the range of measurement error. It is likely a small increase such as this is a result of changes in measurement technique rather than a true increase in body fat.
RELATED ARTICLE: Techniques Used to Determine Body Fat Percentage
Measurement Technique Component Measured Anthropometry Measures body segment circumferences.
Bioelectrical Impedance Analysis Measures resistance to electric current (BIA) passed through the body. Predicts body
water content, lean body mass, and body
fat.
Dual energy X-ray absorptiometry X-ray technique at two energy levels. (DEXA) Used to image body fat or calculate bone
mass.
Infrared Interactance Infrared light passes through tissues.
Magnetic Resonance Imaging Magnetic field and radio-frequency waves (MRI) similar to CAT scan. Useful for measuring
deep abdominal fat.
Skinfold Thickness Measures subcutaneous fat folds.
Underwater Weighing Full body submersion to measure water
displacement. Predicts body density, body
fat and lean body mass.
Disease Risk
According to
Waist-to-Hip Ratio
[TABULAR DATA OMITTED]
Disease Risk
According to Body
Mass Index
BMI Disease Risk
20.00-24.99 Very low
25.00-29.99 Low
30.00-34.99 Moderate
35.00-39.99 High
[greater than or equal to]40.00 Very high
Deborah Riebe, Ph.D., is an assistant professor in the Department of Physical Education and Exercise Science at the University of Rhode Island. Ronan Hingerty, B.S., is a graduate student in exercise science at the University of Rhode Island.
COPYRIGHT 1996 Aerobics and Fitness Association of America
COPYRIGHT 2004 Gale Group