@onehottrail's carnivore diet testosterone claims, fact-checked

What did @onehottrail actually say?

The creator analyzed a carnivore diet influencer claiming "over 1100 nanograms per deciliter total testosterone naturally." Rather than just accepting that as a win, @onehottrail ran the math and concluded something more complicated is happening. The headline number looks great. The story underneath it is murkier.

Specifically, the creator estimated that a free testosterone reading of 16.05 ng/dL against a total of roughly 1,150 ng/dL implies a sex hormone-binding globulin (SHBG) level of approximately 70 nmol/L. That estimate is reasonable back-of-envelope math. The creator then argues that elevated SHBG, not exceptional hormonal health, is responsible for the high total testosterone, and that "secondary iron overload" from heavy red meat consumption is the likely driver. That last part is where things get more speculative.

Does the science back this up?

The SHBG math is solid. The iron overload hypothesis is plausible but stated with more confidence than the current evidence supports.

SHBG binds testosterone tightly, and the body does respond to lower free testosterone bioavailability by increasing LH-driven production, which pushes total testosterone up. This is well-documented. A 2020 paper by Pilz et al. in the journal Hormone and Metabolic Research confirmed that SHBG is a key determinant of the free-to-total testosterone ratio and that high SHBG can produce misleadingly elevated total testosterone readings.

The iron-SHBG connection is less settled. Some research, including work by Ellervik et al. (2007, Clinical Chemistry), has found associations between iron status and SHBG, but the directionality and magnitude in a carnivore-specific context have not been rigorously studied in randomized trials. The creator presents this as the "likely reason" when it is more accurately a reasonable hypothesis.

What did they get wrong (or right)?

They got the SHBG framing largely right, and that deserves credit. Most fitness influencers treat total testosterone as the only number that matters. It is not. Free testosterone is what actually enters cells and drives androgenic effects, and a free fraction of 1.4% is at the low end of normal, not something to brag about.

Where the creator oversimplifies is the reference range claim. They state SHBG "tops out around 15 nanomoles per liter" for most labs. That is incorrect. Standard adult male reference ranges for SHBG typically run from about 10 to 57 nmol/L, depending on the lab and the age of the individual. Quest Diagnostics and LabCorp both list upper limits well above 15. An SHBG of 70 is elevated, yes, but the framing of 15 as the ceiling is a significant error that exaggerates the abnormality.

The "secondary iron overload" claim also needed more qualification. Hereditary hemochromatosis causes secondary SHBG changes, but dietary iron overload from carnivore eating producing the same effect is not established by strong clinical data.

What should you actually know?

Total testosterone alone is a poor measure of androgenic status, full stop. If you are evaluating hormone health, you need free testosterone, SHBG, albumin, LH, FSH, and a full metabolic panel at minimum. A number like 1,100 ng/dL looks exceptional until you realize the bioavailable fraction may be unremarkable.

SHBG is elevated by a range of factors including liver function, thyroid status, low insulin, low body fat, and yes, possibly high dietary protein and fat patterns. Anyone adopting a carnivore diet who sees high total testosterone should not assume they are optimized. They should check SHBG and calculate free testosterone using the Vermeulen equation, which is more accurate than a simple percentage.

If SHBG is genuinely elevated above 60 nmol/L, a clinician should investigate causes including liver disease, hyperthyroidism, and in some cases genetic hemochromatosis, before attributing it to diet alone. The creator is right that this person needs more comprehensive bloodwork. That part is not controversial.