Does high SHBG cause high testosterone, or is it the other way around?

What did @t_nutrition_fitness actually say?

The creator is following up on a previous experiment where they ate low protein for a period of time. They report their SHBG climbed into the 100s nmol/L and their total testosterone hit 1,400 ng/dL. After returning to normal protein intake, both numbers started dropping. Their core argument: "the testosterone is downstream of the SHBG," meaning SHBG rising caused total testosterone to rise, not the other way around. They also argued that their free testosterone stayed completely normal throughout, which is why the high total testosterone number was essentially meaningless for muscle growth purposes.

They were responding to a viewer who asked whether lowering SHBG would let them capitalize on that high testosterone. The creator said no: if SHBG drops, total testosterone drops with it, so there is no muscular benefit to lowering SHBG in this context.

Does the science back this up?

Mostly, yes. The SHBG-testosterone relationship is real and well-documented, though the causal framing is more complicated than the creator suggests. SHBG binds testosterone in the bloodstream, and because SHBG-bound testosterone has a longer half-life, elevated SHBG can accumulate total testosterone over time. Ramasamy et al. (2018, Journal of Clinical Endocrinology and Metabolism) confirmed that total testosterone tracks closely with SHBG levels, and that free testosterone is a far better predictor of androgen bioavailability.

The free testosterone argument is also solid. Vermeulen et al. (1999, Journal of Clinical Endocrinology and Metabolism) established that only free and loosely albumin-bound testosterone actually enters cells and activates androgen receptors. High total testosterone with normal free testosterone is genuinely not meaningfully anabolic. The creator gets this right.

What did they get wrong (or right)?

The directional claim, that SHBG "causes" high testosterone, is an oversimplification worth flagging. SHBG does not produce testosterone. What happens is that high SHBG extends the circulating half-life of bound testosterone, which can make total testosterone measurements look elevated. The pituitary axis also plays a role: LH and FSH regulation can shift in response to changes in free testosterone, not SHBG directly. Swerdloff and Wang (2011, New England Journal of Medicine review) note that the HPG axis responds to free androgen levels, not SHBG concentrations per se.

That said, the practical conclusion, that lowering SHBG in this scenario would not produce a net muscular benefit, is defensible. If SHBG drops and free testosterone stays flat or declines, there is no anabolic gain. The creator's logic holds at the practical level even if the mechanistic language is loose.

One thing they did not address: why did a low protein diet elevate SHBG in the first place? That mechanism, likely involving insulin signaling and hepatic SHBG production, would have added useful context. Insulin suppresses hepatic SHBG synthesis (Plymate et al., 1988, Journal of Clinical Endocrinology and Metabolism), so low protein may have altered glucose and insulin dynamics enough to raise SHBG. That part went unexplained.

What should you actually know?

Total testosterone is a frequently misread number in fitness and TRT conversations. It tells you how much testosterone is floating around in your blood, not how much is actually available to your cells. Free testosterone, typically calculated or measured via equilibrium dialysis, is the number that matters for androgenic effects. Clinically, most hypogonadism diagnoses lean on free testosterone thresholds, not total testosterone alone.

SHBG levels are influenced by a wide range of factors: diet composition, liver function, thyroid status, insulin sensitivity, age, and certain medications. The idea that you can simply "lower your SHBG" as a performance strategy ignores how interconnected these systems are. Attempting to manipulate SHBG without clinical guidance can produce unpredictable hormonal shifts. If you are on TRT or considering it, this is a conversation for a licensed clinician reviewing your full panel, not a TikTok comment.

The creator's blood work was sponsored by Marek Health, a telehealth platform. That relationship is disclosed, which is appropriate. It does not invalidate the information, but you should know the context when evaluating any sponsored content involving lab results.