Assessing the Flab Quotient

Last time, Childhood Obesity looked at body mass index as the standard of obesity measurement. A study published in the American Journal of Clinical Nutrition examined the specific question of whether BMI or waist circumference (WC) measurement is best. When someone is apparently healthy, albeit chubby, that person’s system may still betray early warning signs of cardiometabolic risk.

Will this person eventually develop diabetes or heart disease? Blood tests reveal certain chemical markers that throw a shadow of doom over a person’s health picture. Scientists wondered whether those lab results match up more with overall obesity as measured by BMI, or central obesity as measured by WC. The answer is, both “indexes of excess adiposity” correlate with bad news in the test tube.

Actually, there are several ways to calculate the ratio of body fat to whatever else is in there. One problem is, these methods may be too complicated and expensive to implement on a large scale, such as all across the USA for all children. Jeremey DuVall of Men’s Fitness has catalogued them.

How to measure

Fanciest of all is the DEXA or Dual-energy X-ray Absorptiometry Scan, which can “estimate lean tissue, bone, mineral, and fat across regions of the body with amazing accuracy.” Of course the potential cost for use in schools is unimaginable. Underwater weighing is quite accurate, but totally impractical in most situations. The space and equipment needed are problematic, and the minute anyone in a position of authority tells a child to strip down and get underwater, trouble will ensue.

And then there is Whole Body Plethysmography, which “measures air displacement to estimate body composition” — basically, underwater weighing without the water. In terms of widespread use in schools and similar institutions, this would be much more culturally acceptable. But the equipment is prohibitively expensive, and of course the method also requires trained personnel.

Skinfold measurement, by comparison, is downright primitive. All you need is a pair of calipers. Once the amount of subcutaneous fat is determined, that amount can be extrapolated to the rest of the body to estimate total fat percentage, including the lard strangling our kidneys and livers. Du Vall says:

The most common variations are the 3-site and 7-site skinfold tests. Sites are slightly different between men and women, but the protocol remains the same. Skinfold measurements remain as a popular and widely used method of measuring changes in body composition since calipers are easy to use and found at almost any gym.

Of course you also need someone wielding the calipers who knows what they’re doing and what it means, but the skill is easier to learn than, for instance, DEXA technology. The last suggestion, Bioelectrical Impedance Analysis (BIA) is cheap and widely available. Electrical signals travel through fat differently than through lean tissue. The hitch is, variable factors like hydration level can skew the results.

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