SHBG during weight loss: what actually moves?

SHBG is a protein that binds sex hormones in your blood and carries them around. Its full name is sex hormone binding globulin. Your liver produces it.

SHBG is not a hormone itself. It is a transport protein.

SHBG binds testosterone and oestradiol, but not equally firmly. The bond with testosterone is strong, the one with oestradiol clearly looser. Anything attached to this protein cannot be used by your tissues.

Your total testosterone adds bound and unbound hormone together. Your SHBG decides how that total splits. That is why free testosterone is calculated from the pair.

Results are reported in nmol/l. The normal range depends on your sex and on your age group.

Look closely at the second row. SHBG rises with age in men, so the ceiling climbs to 76.7 nmol/l. A man of 60 with a value of 70 sits inside his own band.

Judge him against the younger band and the same result looks high. The reverse also holds: 19 looks normal while his floor is 20.6 nmol/l. One flat band per sex simply does not work here.

Every laboratory sets its own band, depending on the analyser it runs. We work with a network of independent, certified laboratories across the Netherlands. They do not all run the same equipment, so the bands vary. The values printed on your own report therefore outrank the table above.

For you there is one more layer. A table tells you where a population sits, not where you started. During a weight-loss programme your own baseline is the reference point you need.

There is one reason SHBG belongs on a metabolic panel: it moves with your insulin balance. The dominant cause of a low SHBG is a persistently high insulin level. That high insulin travels with insulin resistance and with excess fat tissue.

Your liver then produces less SHBG. As your insulin sensitivity improves while you lose weight, your SHBG usually climbs back.

That makes this value unusual on a panel. Most blood values describe an organ or a store. SHBG describes the process your programme is trying to change.

So have your fasting insulin and your HbA1c measured in the same draw. When all three move the same way, you read one story instead of three loose figures.

The second reason is your testosterone. Without SHBG a testosterone result cannot be read properly, and this runs in both directions. A low SHBG pulls your total testosterone down while your free testosterone stays normal.

A high SHBG does the opposite: the total holds up, but less free hormone remains. Say you carry a lot of excess weight and test only a total value. That easily produces a misleading figure.

The same applies to a woman using the pill.

There is a third point, and it needs care. Across large population studies, a low SHBG is linked to more type 2 diabetes. That holds in men and in women.

It is a link between groups of people, nothing more. A blood test cannot predict disease and does not make a diagnosis. So do not read a low value as a verdict on your future.

Treat it as a reason to measure your glucose control alongside it.

In practice this means the direction tells you more than the figure. Take a baseline before you start, then repeat at around three and around six months. Has your SHBG gone from 22 to 34 nmol/l while your weight fell?

That is a meaningful movement. Both figures can sit comfortably inside the same reference band. Without that baseline you would never have seen the change.

With SHBG what matters for you is a series of measurements, not a single draw. The cadence that suits a supervised weight-loss programme is straightforward. Take a baseline before you start. Measure again at around three months, and once more at around six months.

That first measurement matters most, and it is the one most often skipped. Without a baseline you cannot tell later whether 34 nmol/l is a rise or a fall. That direction is exactly the information you are after.

Request your fasting glucose in the same draw, plus your total testosterone. Free testosterone is calculated from that pair, so the two belong together on the form. A total testosterone value without SHBG is hard to interpret. That is especially true with a lot of excess weight.

Test in the morning and fasted, so your glucose and insulin are usable. SHBG itself is not especially sensitive to the time of day. Do not measure shortly after an infection, an operation or a spell of illness. Such a data point contaminates your series without anything in your metabolism having changed.

Use the same laboratory each time where you can. Different analysers work with different bands. You would then be comparing figures on two different scales. If the laboratory does change along the way, note that next to your result.