Depending on which Japanese conglomerate you believe, either I have the body of a 25-year-old or I'm pushing 70.
Which is disconcerting either way, because I was a mess when I was 25, and I'd prefer to let 70 wait its turn.
But according to the statisticians at companies such as Omron and Tanita, my “metabolic age'' lies at one of those extremes.
Metabolic age is a statistical construct that is being built into the “body composition'' monitors proliferating on store shelves.
How it works
The main purpose of body composition monitors is to measure body fat.
These devices use a technology called bioelectrical impedance, which passes a small current through conductive foot pads or handheld electrodes (and in some cases, both).
The current can pass easily through water-rich muscle fibre but it bogs down in fat. Based on a measure of impedance (how much of the current gets through from one electrode to the other), the devices use mathematical models to estimate the amount of fat that got in the way en route.
This is a good idea because it is widely acknowledged that people should be less concerned with their weight than whether that weight comes from fat or muscle.
Some companies are loading their products with lots of other features: estimates of how much muscle you have, how many pounds of bone, hydration levels, the amount of “visceral fat'' larded around your vital organs, how many calories you need to eat daily — and, based on all of the above — how old you are.
To determine the accuracy of retail-grade monitors in measuring body fat, I gathered some models and matched them against two clinical methods for taking the same measurement: a hydrostatic “dunk tank'' test often used in research and the hand-calipers pinch test often performed in health clinics and gyms.
The two clinical measures, taken by doctoral student Andy Ludlow at the University of Maryland, raises a point that representatives for the monitor companies emphasise: even accepted standards such as the dunk tank, which uses formulas related to the displacement of water and the comparative density of muscle and fat, are only estimates.
In the case of the body composition monitors, the mathematical models involved have many built-in assumptions — particularly when it comes to things such as visceral fat — and if your body strays from that norm, results will be less accurate.
Company representatives say their products should be used more to establish trends than for precise measurements.
These devices give you a rough sense of where you stand but are better used to see whether your body fat percentage is going up, down or staying steady over time.
For example, if you're losing weight and your body fat is creeping higher, that's a sign of unhealthy dieting — weight loss through dehydration or the destruction of muscle
tissue.
However, if your body fat readings are going down but the scales are not budging, that's a sign that you're building muscle and getting stronger.
Take it easy
“We tell everybody it's just a tool. It's not an absolute'' said Keith Erickson, director of North and South American sales for Tanita.
Anyone considering a purchase should keep in mind that they are twitchy, especially when it comes to hydration levels.
If you're attracted to technology and like to quantify things, this is a reasonable purchase, used correctly. But here's an alternative: Contract your abs and grab your belly. Anything in your hands doesn't need to be there.
