The four things you'd lose by not watching
The four things you'd lose by not watching
Only morning light exposure from Huberman's routine is unambiguously beneficial for women; fasted training, delayed caffeine, and ice baths are either harmful or less effective.
To avoid a cortisol spike, women should consume caffeine alongside a meal containing protein and carbohydrates, not on an empty stomach.
Ice baths place too much sympathetic stress on women, pushing them into survival mode; cool water (10–16°C) provides some benefit but sauna (10 min post‑training) yields greater metabolic and vascular improvements.
A female-adapted morning routine: eat before training, pair caffeine with food, get morning light, and hit the sauna after exercise.
Concrete recipes — what, when, how much, and why
fasted training isn’t great for women.
The original Huberman protocol delays caffeine for 90 minutes after waking to let the natural cortisol awakening response subside. Sims points out that for women, this is unnecessary if caffeine is paired with food. The female hypothalamus is particularly responsive to nutrient intake; when protein and carbohydrate arrive together with caffeine, the brain signals the adrenal glands to reduce cortisol output. This removes the stress‑hormone spike and any associated negative effects on mood, metabolism, or training. The rule becomes: no fasting caffeine, and pairing eliminates the waiting period.
Nutrient sensing in the hypothalamus detects amino acids and glucose, leading to decreased corticotropin‑releasing hormone (CRH) and adrenocorticotropic hormone (ACTH) release, which in turn blunts the cortisol response from caffeine.
If you want your caffeine, make sure that it is with some protein and carbohydrate so that we can offset that cortisol peak.
Light exposure, definitely. We want that light exposure for circadian rhythm.
Sims notes that heat exposure for women triggers a cascade of beneficial adaptations. Metabolically, it improves glucose handling. The heat‑shock response involves uncoupling proteins that enhance mitochondrial efficiency and cellular repair. Vascularly, repeated heat exposure leads to better vasodilation and vasoconstriction, lowering blood pressure. Because women’s thermoregulation differs—particularly during the follicular and luteal phases—they actually tolerate heat better than men. Sims leverages this by placing sauna straight after training, which she says “extends your training stress load” and feeds forward into long‑term health. Men can still use sauna, but the physiological edge is female‑specific.
Heat stress activates heat‑shock proteins (HSPs) and uncoupling proteins (UCPs), which improve mitochondrial function and cellular resilience. Improved vasodilation is mediated by nitric oxide and endothelial adaptations, reducing peripheral resistance and blood pressure. Glucose control improvements likely stem from increased insulin sensitivity in skeletal muscle post‑heat exposure.
get in the sauna for 10 minutes because one, that’s going to extend your training stress load and improve your training responses, but it’s also going to feed forward into better health outcomes.
Sims draws a sharp line between cool and ice‑cold water. Research and practical anecdotes show that when women are submerged in ice water, the sympathetic nervous system fires excessively, and the body enters a defensive survival mode rather than engaging the parasympathetic rebound and metabolic improvements that men experience. This sex difference likely involves hormonal modulation of the autonomic nervous system and thermoregulatory pathways. Cool water (10–16°C) still provides a mild hormetic stress—shivering, non‑shivering thermogenesis, and some parasympathetic activation—but the magnitude is dampened compared to men. For women keen on ocean dips, Sims says the sea temperature of 14°C around New Zealand is “cold enough” and safe. She frames the sauna as a more potent and appropriate stressor for female physiology, making cold water a secondary, optional practice.
Excessive cold triggers an over‑activation of the sympathetic nervous system via the locus coeruleus‑norepinephrine system, with heightened release of epinephrine and norepinephrine. In women, this can override the beneficial cold‑induced parasympathetic rebound and instead cause peripheral vasoconstriction, tachycardia, and a stress‑hormone surge that aborts mitochondrial biogenesis and brown‑fat activation.
Sims reports having been “slammed on social media” for advocating against ice baths for women, indicating that this guidance is highly controversial and that she has personally faced backlash for it.
women shouldn’t be doing ice baths or cold plunge because it’s too much of a stress on the body.
Personal practice updates, fresh positions, predictions
Stacy Sims argues that Huberman’s popular protocol—fasted exercise, delayed caffeine, cold immersion—is largely “bro science” for women. Only morning light exposure is equally good; the other pillars need to be modified or avoided.
Why this matters: Challenges a widely adopted, male-centric biohacking prescription by detailing physiological sex differences that make it unsuitable for women.
Andrew Huberman’s morning routine (early light, no caffeine for 90 minutes, fasted training, cold plunge) had been presented as a universal optimisation, gaining massive adoption among both men and women.
Stacy Sims and her colleagues reviewed the entire protocol and concluded that only the light‑exposure component transfers cleanly to women. The caffeine rule fails because, when women eat alongside caffeine, the hypothalamus detects incoming nutrition and down‑regulates the cortisol spike—negating the reason for the delay. Fasted training exacerbates female‑specific hormonal strains (the transcript references a longer prior discussion; she states it simply isn’t great for women). Ice baths are the most problematic: they trigger an excessive sympathetic response that pushes women into a survival state, whereas men get metabolic and parasympathetic benefits. Even cool water (10–16°C) yields less robust changes in women compared to men. By contrast, heat exposure delivers pronounced advantages for women: better glucose control, improved heat‑shock protein responses, enhanced vasodilation, and lower blood pressure. Sims essentially flips the protocol—keeping light, requiring food, trading cold for heat, and adjusting caffeine timing.
the light exposure is the only one that’s really good for women.
Women derive more robust metabolic and vascular benefits from sauna (heat) than from cold immersion, and ice baths are outright harmful because they push women into a sympathetic survival mode.
Why this matters: Contradicts the prevailing cold‑plunge trend and identifies a sex‑dependent harm that is absent in men.
Cold exposure has been promoted as a hormetic stress that improves resilience, noradrenaline, and metabolism, with many protocols advocating ice‑cold water.
Sims explains that when women enter ice‑cold water, the sympathetic nervous system overreacts to an extent that shifts the body into survival mode rather than a productive hormetic response. This prevents the beneficial parasympathetic and metabolic adaptations that men experience. Even at cool (10–16°C) temperatures, the metabolic and parasympathetic changes are present but still “not as robust” as in men. Heat exposure, however, plays to female physiology. Sauna increases metabolic activity, improving glucose regulation; it triggers heat‑shock proteins that assist in cellular repair and uncoupling; and it enhances vasodilatory and vasoconstrictive responses, leading to better blood pressure control. Men also benefit from heat, but they tolerate it less well due to thermoregulatory differences, making sauna a particularly female‑friendly intervention. Sims therefore recommends post‑exercise sauna and, if women still want cold water, staying in the 10–16°C range—never ice.
Sims recounts being “slammed on social media” a couple of months prior for publicly saying women shouldn’t do ice baths or cold plunges, which illustrates how entrenched the male‑default advice is and how provocative her counter‑stance was.
women shouldn’t be doing ice baths or cold plunge because it’s too much of a stress on the body.
Lines worth pulling out — contrarian, specific, or perfectly phrased
yeah that’s very bro science.
the light exposure is the only one that’s really good for women.
women shouldn’t be doing ice baths or cold plunge because it’s too much of a stress on the body.
if I were to design a protocol and have the voice of Andrew, then I would say for women, let’s get up and have some food before we go training. If you want your caffeine, make sure that it is with some protein and carbohydrate so that we can offset that cortisol peak. … get in the sauna for 10 minutes.
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Educational summary of the cited expert source — not medical advice. Open the source recording linked above and consult a qualified physician before acting on any protocol.
