What did @onehottrail actually say?
The creator argues that very high protein diets, not just low-fat diets, can suppress testosterone levels in natural athletes. He claims the mechanism involves the urea cycle: excess protein raises cortisol, which upregulates urea processing, while testosterone gets suppressed in the process. He also says he capped protein at 2.4 grams per kilogram during his 12-week cut and kept fat at 35% of total calories to protect his hormones.
The practical warning is directed at guys who "fat deprived the sh** of themselves" while maximizing protein during a cut, leading to what he calls "crashed hormones." He uses his own free testosterone levels as anecdotal evidence that his approach worked. That self-reported data point is essentially worthless as evidence, but the underlying claims deserve a real look.
Does the science back this up?
Partially, yes, though the picture is messier than the video implies. The relationship between very high protein intake and testosterone suppression has real data behind it, but it is not a clean dose-response curve, and most of the effect sizes are modest.
Anderson et al. (1987, Journal of Applied Physiology) remains one of the most cited studies here. Men shifted to a high-protein, low-fat diet showed significantly lower total testosterone compared to a high-fat, lower-protein baseline. A 2021 meta-analysis by Whittaker and Wu in Nutrition Reviews pooled data across dietary studies and found that higher protein intakes were associated with modestly lower testosterone, while higher fat intakes, particularly saturated and monounsaturated fats, correlated with higher testosterone. The effect was real but not dramatic in most healthy men.
The urea cycle mechanism the creator describes is plausible and discussed in the literature, but it is a hypothesis, not an established pathway. He does say "the authors hypothesize," which is accurate framing. Cortisol's role in upregulating the urea cycle and its inverse relationship with testosterone is biologically coherent, supported broadly by HPA axis research, though the direct causal chain he describes has not been cleanly isolated in human trials.
What did they get wrong (or right)?
He got the core directional claim right. Low-fat diets suppress testosterone, and extremely high protein intakes appear to do the same, likely through different mechanisms. His protein target of 2.4 grams per kilogram is actually well-supported by the muscle retention literature. Stokes et al. (2018, Journal of the International Society of Sports Nutrition) found that 2.4 grams per kilogram was sufficient for lean mass preservation during a deficit, with no clear benefit to going higher.
Where he goes wrong is the implied precision. He presents 35% fat as if it is a calibrated hormonal protection threshold. The research does not support a specific fat percentage cutoff. Studies show testosterone problems emerge when fat drops below roughly 15-20% of calories, but 35% is not a magic number backed by evidence. It may be a reasonable personal choice, but framing it as a protocol is overreach.
His own free testosterone data is also anecdotal from a single individual with no control condition. It is not evidence of anything beyond his personal experience.
What should you actually know?
If you are a natural athlete cutting calories, the evidence does support being careful about both fat and protein extremes. Dropping dietary fat too low is the more consistently documented testosterone suppressor. The high-protein effect is real but secondary, and it likely only becomes meaningful at intakes well above 3 grams per kilogram of body weight sustained over time.
A protein intake around 2.2 to 2.6 grams per kilogram during a cut is supported by both the muscle retention data and appears to avoid the range where hormonal suppression becomes a documented concern. Keeping fat above 20% of total calories is a reasonable floor based on available evidence, though 35% is not specifically validated as a target.
- Do not cut fat below 15-20% of total calories if you care about testosterone levels.
- Protein intakes above 3 to 3.5 grams per kilogram may be unnecessary and potentially counterproductive hormonally.
- Blood urea nitrogen rising on a high protein diet is expected and not inherently dangerous in healthy individuals, but it is a real physiological signal worth monitoring.
- Individual hormone responses vary significantly based on training status, sleep, stress, and total caloric deficit depth.
If you are experiencing symptoms of low testosterone, self-diagnosing based on macronutrient ratios and Instagram content is not a substitute for actual bloodwork and a conversation with a clinician.