Low Testosterone and Body Composition in Men

Picture a 47 year old man who comes in tired, a little heavier around the middle than he was five years ago, and stuck at the same weights in the gym. His last physical said everything looked normal, and testosterone was never checked. This pattern is common, and body composition is often where it shows first.

What testosterone does to muscle and fat

Testosterone signals muscle cells to build protein. With less of it, muscle is harder to build and easier to lose, and recovery from training slows. Testosterone also affects where fat goes. Men with low levels tend to carry more fat overall and more of it as visceral fat, the fat around the organs.

The relationship runs in both directions. Fat tissue contains an enzyme called aromatase that converts testosterone into estradiol. The more fat a man carries, especially visceral fat, the more testosterone gets converted, and the lower his level drifts. Lower testosterone then makes it easier to gain fat. Poor sleep, heavy drinking and certain medications can push the same loop.

Bone is part of this too. Testosterone, and the estradiol made from it, help maintain bone density in men. Men with low levels for years can lose bone without knowing it.

How we diagnose it

Low testosterone is a diagnosis made from symptoms plus labs, not a single number. We draw it in the morning, when levels are highest, and confirm a low result on a second test. A total testosterone below about 300 ng/dL on two morning draws, with symptoms, is the usual threshold. We also look at free testosterone, SHBG, estradiol and the pituitary hormones, because the cause matters for the treatment.

What a DEXA scan shows

A DEXA scan puts numbers on the physical side of the picture:

• Body fat percentage, which tells us more than BMI ever will
• A visceral fat estimate
• Lean mass in the arms, legs and trunk, and ALMI, the muscle index we compare to age and sex percentiles
• Bone density at the spine and hip

This matters before and after any decision about treatment. If a man has high visceral fat and normal muscle, losing fat may bring testosterone up on its own. If he has low lean mass and low bone density with a confirmed low level, that changes the conversation. When men with a true deficiency are treated, studies show a modest gain in lean mass and a modest drop in fat mass, and a repeat scan about every 6 months shows whether that is actually happening.

Getting hormones where they should be is part of what we do, and so is measuring whether it worked. That's the kind of thing we look at.

Book a DEXA scan at HYBRD Health ($199)

This article is educational and is not medical advice.