Using Your DEXA Scan Results

2011-04-01 updated 2011-09-13 • SEND FEEDBACK •
Related: body fat, health, metabolism, training

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Ideally, a DEXA scan can be done 2-3 times per year when engaged in a body composition change program (“weight loss” is a nebulous goal, since it ignores muscle versus fat). DEXA scans are not a long-term suggestion, since some low-dose X-Rays are involved. But the dose is very low, less than that of an airline flight from California to New York and back.

Too high or too low is not ideal

No one needs to be 20% body fat— it’s far from ideal, and feels heavy. And no one needs to be less than 5% body fat except Tour De France riders and Olympic athletes because it’s potentially dangerous in case of a serious injury or illness. With very low body fat, it’s also harder to maintain core body temperature in water or on cold days though it’s a big help in shedding body heat on hot days.

A reasonable target for serious male athletes is 8% body fat, and for women, something in the 10-12% range. Drop a few percent off for body typse that are naturally lean, or for ultra-serious athletes. Note that women may cease to menstruate if body fat drops too low.

Targeting muscle and fat

DEXA focuses on the actual percentage of muscle and fat, which can be used for a rational approach to your ideal body weight based on current body fat, bone density and muscle mass.

Body fat of 20.6% feels awful to me. I feel heavy at that level, though most people would consider me in great shape by looking at me. With 12% body fat, I feel lean and perky, simple things like standing up, going up steps, etc all are much easier. Health is about feeling good, and from that perspective, 20% body fat is not health, since it impedes movement and carries increased risk of back and joint pain from exertion (simply by virtue of the extra weight).

Percent fat and muscle

Up the muscle, reduce the fat

By increasing muscle mass, the percent body fat decreases naturally as more calories are required to maintain muscle. A loss of muscle mass is a self-defeating approach that weakens the body, yet it is the result of many popular diets. So the challenge is to lose body fat, and maintain or gain muscle, simultaneously. Muscle is also more dense, leading to a slimmer body even at the same weight.

Diets

Diets that focus on body weight are incompetent or worse: perhaps the weight loss is mostly muscle, a disastrous result. Or perhaps losing 5 pounds of fat and gaining 5 pounds of muscle shows zero weight difference, but a major difference in terms of health.

Simplistic diet approaches in the long run are self-defeating. All major dietary fads and food programs these days revolve around money in one way or another, so caveat emptor. Extremes such as ultra low fat, very high protein, and other goofy approaches are not healthy, but do make the book authors and TV-show hosts rich.

Even without a DEXA scan, one can use a tape measure, skin-fold test, time trial or similar athletic approach to deducing increases in strength, which correlate strongly with muscle mass (and body weight, in the case of ascents).

The value of a DEXA scan is a rational and measured approach, which can be confirmed by results on physical challenges or another DEXA scan, or just a glance in the mirror. More importantly, it can set realistic expectations, and provide powerful feedback on progress.

Example Dual-energy X-ray absorptiometry or DEXA scan for your author