Assessment of Overweight and Obesity − Rakyat Biologi

Although accurate methods to assess body fat exist, the measurement of body fat by these techniques is expensive and is often not readily available to most clinicians. Two surrogate measures are important to assess body fat, BMI and waist index.

Body Mass Index (BMI)

BMI is recommended as a practical approach for assessing body fat in the clinical setting. It provides a more accurate measure of total body fat compared with the assessment of body weight alone.

The typical body weight tables are based on mortality outcomes, and they do not necessarily predict morbidity. However, BMI has some limitations. For example, BMI overestimates body fat in persons who are very muscular, and it can underestimate body fat in persons who have lost muscle mass (e.g., many elderly). BMI is a direct calculation based on height and weight, regardless of gender.

You can calculate BMI as follows:

1. Multiply weight (in pounds) by 703

2. Multiply height (in inches) by height (in inches)

3. Divide the answer in step 1 by the answer in step 2 to get the BMI.

Example: for a person who is 5 feet 5 inches tall weighing 180 lbs

Step 1 180 x 703 =126,540

Step 2 65 x 65 = 4,225

Step 3 126,540 / 4,225 = 29.9

BMI = 29.9

Classification of Overweight and Obesity by BMI

	Obesity Class	BMI (kg/m²)
Underweight		<18.5
Normal		18.5-24.9
Overweight		25.0-29.9
Obesity	I	30.0-34.9
	II	35.0-39.9
Extreme Obesity	III	40

The primary classification of overweight and obesity is based on the assessment of BMI. It should be noted that the relationship between BMI and disease risk varies among individuals and among different populations. Some individuals with mild obesity may have multiple risk factors; others with more severe obesity may have fewer risk factors.

Clinical judgment must be used in interpreting BMI in situations that may affect its accuracy as an indicator of total body fat. Examples of these situations include the presence of edema, high muscularity, muscle wasting, and individuals who are limited in stature. The relationship between BMI and body fat content varies somewhat with age, gender, and possibly ethnicity because of differences in the composition of lean tissue, sitting height, and hydration state. For example, older persons often have lost muscle mass; thus, they have more fat for a given BMI than younger persons. Women may have more body fat for a given BMI than men, whereas patients with clinical edema may have less fat for a given BMI compared with those without edema. Nevertheless, these circumstances do not markedly influence the validity of BMI for classifying individuals into broad categories of overweight and obesity in order to monitor the weight status of individuals in clinical settings.

Waist Circumference

Waist circumference is the most practical tool a clinician can use to evaluate a patient’s abdominal fat before and during weight loss treatment. Computed tomography and magnetic resonance imaging are both more accurate but are impractical for routine clinical use. Fat located in the abdominal region is associated with a greater health risk than peripheral fat (i.e., fat in the gluteal-femoral region). Furthermore, abdominal fat appears to be an independent risk predictor when BMI is not markedly increased.¹⁵ Therefore, waist or abdominal circumference and BMI should be measured not only for the initial assessment of obesity but also for monitoring the efficacy of the weight loss treatment for patients with a BMI < 35.

High risk waist measurements:

Men: > 40 in (> 102 cm) Women: > 35 in (> 88 cm)

A high waist circumference is associated with an increased risk for type 2 diabetes, dyslipidemia, hypertension, and CVD in patients with a BMI between 25 and 34.9 kg/m2 .

Measuring Waist Circumference

To measure waist circumference, locate the upper hip bone and the top of the right iliac crest. Place a measuring tape in a horizontal plane around the abdomen at the level of the iliac crest. Before reading the tape measure, ensure that the tape is snug, but does not compress the skin, and is parallel to the floor.

The measurement is made at the end of a normal expiration.

Although waist circumference and BMI are interrelated, waist circumference provides an independent prediction of risk over and above that of BMI. The waist circumference measurement is particularly useful in patients who are categorized as normal or overweight in terms of BMI. For individuals with a BMI = 35, waist circumference adds little to the predictive power of the disease risk classification of BMI. A high waist circumference is associated with an increased risk for type 2 diabetes, dyslipidemia, hypertension, and CVD in patients with a BMI between 25 and 34.9 kg/m.

Monitoring changes in waist circumference over time may be helpful; it can provide an estimate of increases or decreases in abdominal fat, even in the absence of changes in BMI. Furthermore, in obese patients with metabolic complications, changes in waist circumference are useful predictors of changes in cardiovascular disease (CVD) risk factors. Men are at increased relative risk if they have a waist circumference greater than 40 inches (102 cm); women are at an increased relative risk if they have a waist circumference greater than 35 inches (88 cm).

There are ethnic and age-related differences in body fat distribution that modify the predictive validity of waist circumference as a surrogate for abdominal fat.In some populations (e.g., Asian Americans or persons of Asian descent), waist circumference is a better indicator of relative disease risk than BMI.

For older individuals, waist circumference assumes greater value for estimating risk of obesity-related diseases.