Previously we have discussed the obsessive epidemic, the Surgeon General's warning, associated risks of this condition, the definition of obesity and overweight, as well as some of the excuses and lifestyle factors associated with obesity.
In this issue we will discuss some methods of fat calculation, and cut off levels associated with increased risk.
Methods of Fat Calculation
There are numerous ways in which to calculate the approximate fat content of an individual's body. Some of the more commonly known methods are BMI (Body Mass Index), DEXA (dual energy x-ray absorptiometry), bioelectrical impedance analysis, skin caliper pinch tests, and underwater weighing.
The most direct measures of body fat, such as underwater weighing or DEXA scanning, are impractical for use. Indirect estimates of body fat are more practical. (1)
Body Mass Index
One of the most commonly used methods is BMI due its ease of use. The calculation for this is BMI = weight (in Kg) / height (m) ². The values for different ages show relative health risks.
Although BMI has been used to evaluate overweight and obesity in adults for many years, it has recently been recommended for the screening of children and adolescents. With this change you can use it from the age of 2 years through to adulthood. However, BMI is used differently to define overweight in children and adolescents than it is in adults. (2)
Overweight in children and adolescents is defined as a BMI-for-age at or above the 95th percentile on the CDC growth charts. The risk of overweight for ages 2-20 years is defined as a BMI-for-age between the 85th and the 95th percentiles. (2)
a BMI of 27.3 or more for women and
a BMI of 27.8 or more for men.
The World Health Organization assigns an increasing risk for developing other conditions including hypertension, type 2 diabetes mellitus, and cardiovascular disease for people with higher BMI's as compared to persons of normal weight.
Normal is defined as having a BMI between 18.5 and 25 for those of European descent and for those of Asian descent, a BMI of 18.5 to 23 is normal. (1)
In addition to an increase in total body fat, a proportionally greater amount of fat in the abdomen or trunk, compared with fat in the lower extremities or hips, has been associated with increased risk for diabetes, hypertension, and heart disease for both men and women. For people of Asian descent, abdominal (central) obesity is recognized to be a better indicator of future difficulties than BMI. (1)
This abdominal obesity is commonly reported as a waist-to-hip ratio, but it is most easily quantified by a single measurement done at approximately the belly button. Men are considered to have an increased relative risk for coronary artery disease, diabetes, and hypertension if they have a waist circumference of 40 inches (102 cm) or more; whereas women are at increased risk if their waist circumference is 35 inches (88 cm) or more. (1)
Waist: hip ratios are plotted on a graph according to age and sex. The relative risk associated with the ratio is calculated based on the values plotted.
Thus, an overweight person with abnormal fat patterning may be at high risk for these diseases even if that person is not obese by BMI criteria. (1)
Another thing to consider is that if an individual is heavily muscled, their BMI will not be an adequate predictor of health risk. This is why using a variety of measures will give you a better idea of whether or not you are at an increased risk.
Bioelectrical Impedance Analysis
There are a number of bioelectrical impedance analysis meters on the market. They work on the principle that electrical currents will travel through different tissues at different rates. By sending a small electrical current through your body and measuring the return speed, an approx measure of body fat is attained.
As electricity will follow the shortest route, if you use a scale bioelectrical impedance analysis instrument, you will have an idea of your lower body fat content. If you use a hand held device, it will give you an idea of upper body fat. Both of these tend to miss measuring core body fat. An instrument that passes current through the core will give you a better idea of core body fat. Typical normal values are in the range of 10-20% body fat for men and 15-25% body fat for women. (3)
In the next issue, we will review some information about exercise and how much should be done, different types of exercises that you might want to try, and strategies to implement exercise into your life.
In future issues we will look at diet, caloric restriction, supplementation, and more.
Until next time …
Yours in Health,
Dr. M. Montgomery @ http://www.healthyunderstanding.com
1. Obesity, Jonathan Q. Purnell, MD, Medscape.com
2. Overweight Children and Adolescents: Recommendations for Screening, Assessment and Management, Barbara Polhamus, PhD, MPH, RD; Diane Thompson, MPH, RD; Sandra L. Benton-Davis, BS; Christopher M. Reinold, MPH, RD, LD; Comm. Laurence M. Grummer-Strawn, PhD; William Dietz, MD, PhD., Medscape.com
3. University of Michigan Health System (online)
Disclaimer: As always, check with your health care provider to see if this information applies to you. Due diligence is your responsibility. This information is meant to supplement your knowledge, not to replace your own decision making process or take the place of your health care provider.
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