Evaluation for Obesity

There are three methods to evaluate obesity. The most famous one is Body Mass Index(BMI).

BMI=weight (kg) divided by Square of height (meter).

For adults, BMI below 18.5: underweight; 18.5-24.9: normal; 25-29.9: overweight; 30 and above: obese.

For children and teens, the evaluation of the BMI is a little complicated. You need to plot the BMI number on the CDC BMI-for-age-growth charts (for either girls or boys) to obtain a percentile ranking. Underweight: Less than the 5th percentile; Healthy weight: 5th percentile to less than the 85th percentile; Overweight: 85th to less than the 95th percentile; Obese: Equal to or greater than the 95th percentile.

BMI is used as a standard measurement in the medical field. However, there are three problems to use BMI as an obesity evaluation. First, highly trained athletes with big muscles can have BMI above 30 with little body fat. Secondly, in adults who have lost substantial amounts of muscle mass, the BMI may fail to accurately reflect body fat. Thirdly, the BMI doesn't show the distribution of body fat because the distribution is very important to think whether the person is susceptible to cardiovascular disease or not.

Abdominal fat consists of two kinds of fat. One is just beneath the skin. The other one is inside the abdomen. It is called "visceral fat" which is located around the internal organ. Recent studies have demonstrated that the vascular disease such as myocardial infarction and stroke associated with obesity is correlated particularly with visceral adiposity. There are two explanations for this. Visceral fat has been demonstrated to express more inflammatory cytokines than subcutaneous fat in obese states which bring macrophages into fat. Since circulating markers of inflammation are associated with cardiovascular events, the inflammation triggered by adipose tissue may contribute to increased vascular disease. The other explanation is visceral fat cells release their metabolic products directly into the portal circulation, which carries blood straight to the liver. As a result, visceral fat cells that are enlarged and stuffed with excessive triglycerides pour free fatty acids into the liver. Free fatty acids also accumulate in the pancreas, heart, and other organs. Usually they don't store fat. The organ fatness results in producing impaired regulation of insulin, blood sugar, and cholesterol, as well as abnormal heart function. In conclusion, clinical observations and basic research results agree that excessive fat inside the abdomen is a major contributor to cardiovascular disease.

To evaluate the amount of visceral fat accurately, you need to use computed tomography(CT) or magnetic resonance imaging(MRI). They are expensive. Instead, a simple method is to measure the waist-to-hip ratio. Measure your waist at the navel and your hips at their widest point, usually at the bony prominences.

Ratio=Waist(inches)/Hips(inches).

The risk ratio of a heart attack or stroke is above 0.95(men) and 0.85(women). But many experts prefer the method just to measure waist circumference because it involves one measurement instead of two and it is more accurate and reproducible than the waist-to-hip ratio. Measure your waist at the naval for waist circumference.

Men: Low risk-37 inches and below; Intermediate risk-37.1-39.9 inches; High risk-40 inches and above.

Women: Low risk-31.5 inches and below; Intermediate risk-31.6-34.9 inches; High risk-35 inches and above.

The BMI is more complex, but waist measurement is more prone to errors than measuring height and weight. The BMI is good for the measurement of total body fat, while waist measurement is good for the measurement of visceral fat and estimate of the risk of obesity-related disease.