DEEP READING · READ 902
ROAR (2016) & Next Level (2022) · Stacy Sims · with Selene Yeager
Sims sums up her whole body of work in one slogan: "Women are not small men." Almost all of sports-nutrition and training science was done on male subjects and then assumed to transfer to women — and she says that's wrong, because women run on a physiology continually rewritten by estrogen and progesterone. So she splits a woman's life into two halves across two books: ROAR covers the reproductive years, when you still have a cycle (train, eat, and hydrate with your menstrual cycle), and Next Level covers perimenopause and beyond (once hormones — a layer of natural protection — withdraw, you have to replace them with heavier barbells, harder intensity, and more protein).
Sims holds a PhD in exercise physiology and nutrition science; her original specialty was thermoregulation and hydration (how the body sheds heat and manages fluid and electrolytes), and she later turned her whole focus to "sex differences," a thing mainstream sports science had long neglected. Both books are co-written with veteran health journalist Selene Yeager: ROAR (2016, revised 2024) for women with a menstrual cycle; Next Level (2022) for women going through or approaching menopause. Together they span a woman's full athletic life cycle, from puberty to postmenopause.
Place them on the map: these are flagship works of the "female-specific sports science" wave, amplified further by podcasts like Huberman. What sets them apart from a generic fitness book is that they treat "male and female physiology differ" as a first principle, not a footnote. But one thing must be said up front — Sims is opinionated and speaks with certainty; she is an advocate, not a neutral reviewer, and some of her specific prescriptions run ahead of the current evidence (see the criticism section). The best posture for reading her: grab the big, well-supported principles, and hold a grain of reserve for the fine-grained "train on day X of your cycle" prescriptions.
This is the shared foundation of both books, and it's more than a slogan. Mechanistically, women differ from men on many layers: estrogen makes women lean more on fat for fuel and "spare" glycogen, an advantage in long endurance, but it also means that the moment power and high intensity are needed, women actually need to deliberately top up on carbs; progesterone raises core temperature and increases protein breakdown, so women overheat more easily in the heat and need more protein to repair. Add that plasma volume, electrolyte balance, and the gut all shift at different hormone levels — and the logic of "do what the male athlete does, just scaled down" collapses at the root. Sims's whole project is to turn that correction into concrete, actionable advice.
There's an irony worth naming: women were long neglected by sports science precisely because they were "too much trouble." The fluctuating hormones of the menstrual cycle were treated as a variable that "pollutes" an experiment, so to keep the data clean many studies simply recruited only men — and our understanding of "how women should train and eat" was set back by decades as a result. What Sims is doing is filling in that deliberately skipped blank: hormones aren't noise to be cancelled out; they are the main melody of female physiology.
ROAR splits a cycle roughly into two "hormone phases" and argues for arranging training and fuel to match:
| Low-hormone · Follicular | High-hormone · Luteal | |
| Hormones | estrogen & progesterone both low | estrogen & progesterone both high |
| Body | normal core temp, glycogen flows | core temp up, overheats, more protein breakdown |
| Best for | push high intensity, chase PRs | high intensity harder; prioritize recovery |
| Fueling | as usual | pre-cool, more carbs mid-exercise, more protein |
| Pre-period | — | magnesium, zinc, omega-3 to ease PMS |
Schematic: Sims adjusts gently by phase; but cycle-precise programming is weakly evidenced — go by feel, not a rigid 28-day template.
An honest caveat: this "fine-grained cycle-based programming" is the book's most popular — and most contested — part. Current high-quality evidence isn't strong enough to support strict "periodization" (see the criticism section). Treating it as "notice how you feel in different phases and adjust gently" is sound; treating it as a rigid 28-day timetable you must obey goes beyond what the evidence can guarantee.
This may be Sims's most counter-mainstream and most important point. She strongly opposes fasted morning training and chronic diet-style training in women: a woman's body is far more sensitive to "low energy availability" than a man's, and eating persistently less than you burn disrupts the hypothalamus's control of reproduction and metabolism — mildly, cycle disruption, thyroid and mood effects; severely, it becomes RED-S (Relative Energy Deficiency in Sport, the whole syndrome in which a chronic calorie deficit stops periods, drops bone density, and harms immunity and metabolism). She wants women to eat something before a morning workout and to treat "enough fuel" as part of the training plan — because for many chronically under-eating, over-exercising women, the problem was never training too soft; it was training on empty. Her image: the body is a shrewd accountant, and the moment income runs short it quietly cuts what it deems "non-essential" spending — reproduction (the period) and bone maintenance first. So irregular cycles, constant fatigue, and effort that never pays off are often not bad training but hungry training.
Following from the above: women doing high-intensity work need carbohydrate — not the cause of weight gain, but the fuel for producing intensity. Sims is quite reserved about chronic low-carb / keto (a very-low-carb, fat-dominant way of eating) for active women, especially in perimenopause — she argues this kind of extreme carb restriction tends to suppress the thyroid and sex hormones and drag down high-intensity performance and recovery, a bad trade. Her stance isn't "eat more sugar" but "don't cut out the very fuel women most need." Especially in perimenopause, when hormones are already swinging hard, layering on the extra stress of chronic low-carb often makes hot flashes, sleep, and mood worse. Her practical middle path: put carbs where you actually need them — around training — to support intensity and recovery, rather than either banning them all day or piling them on all day.
Sims's academic roots are in thermoregulation and hydration, so both books care a lot about "how to drink." Her key reminder: chugging plain water alone dilutes the sodium in your blood and can make things worse — effective hydration relies on water plus adequate sodium and other electrolytes, so the water is actually retained and used. This matters especially for women, because in the high-hormone luteal phase, plasma volume and temperature regulation shift, and women dehydrate and overheat more easily. Her advice lands in two places: day-to-day, don't hydrate by "waiting until thirsty then gulping a big glass"; and during exercise (especially long, hot sessions) take electrolytes along with the fluid, not water alone.
Entering perimenopause (the transition of wild hormonal swings before menopause, often starting in the forties), estrogen and progesterone slide and oscillate, and the body shows a cascade of changes: visceral fat accumulates more easily, muscle is lost faster (sarcopenia), bone density falls, recovery slows, often with hot flashes and worse sleep. Sims's core message: the reproductive-years playbook (lots of moderate cardio, light weights for high reps) stops working here and can even hurt you — because moderate-intensity "grey zone" cardio keeps cortisol (the stress hormone) elevated, and the postmenopausal body is more sensitive to cortisol, so the more you jog the more belly fat you store. Many women's first instinct at this stage is exactly "then I'll run more and eat less" — which, Sims says, is flooring the gas and the brake at once, precisely backwards.
Against those changes, Next Level's training direction can be summed up as "polarize" — either genuinely heavy or genuinely fast, and cut the mushy middle of moderate cardio. Three pillars: (1) heavy strength training (heavy loads, low reps) to fight the loss of muscle and strength; (2) true high-intensity intervals / sprint intervals (HIIT / sprint intervals) — short all-out efforts with full rest, to protect metabolism and cardio fitness rather than grinding at moderate intensity; (3) plyometrics (jump training — box jumps, quick take-offs and landings) — using impact loading to stimulate bone, preserve bone density and power, a key to preventing postmenopausal fractures. In a line: after menopause you shouldn't train gentler, but with more nerve. The logic: once you lose estrogen — a "free anabolic and bone-protecting signal" — the body only responds to stronger external stimuli; only heavy enough loads, hard enough sprints, and forceful enough landings can trick a degrading system into maintaining muscle and bone. Lukewarm moderate work gives neither that stimulus nor a favorable trade — it just drains you and raises stress hormones, the worst-value training for a menopausal woman.
Once hormones withdraw, the body's efficiency at building muscle drops, so Sims argues you should get enough protein — more than in the reproductive years — and get a serving in soon after training (she often gives high-protein guidance on the order of "about one gram per pound of body weight," adjusted upward after menopause). She's also a firm advocate for creatine — once dismissed as a "male gym supplement," which she argues has evidence for women, especially peri- and postmenopausal, across muscle, bone, and even the brain, at a common dose of about 3–5 grams per day; she notes creatine's value postmenopause isn't only muscular — it feeds the brain's energy metabolism and may help with the brain fog, mood, and fatigue common in menopause. She also addresses the place of hormone therapy (HRT, replacing the estrogen/progesterone that drop after menopause): not a cure-all, but a reasonable option for some women — while stressing that getting training, nutrition, and sleep right first is the foundation.
Here's the one thing both thick books keep circling, said once and clearly: they are two halves of one throughline.
The throughline is "women are not small men"; the two halves apply that principle to the two utterly different hormonal environments of a woman's life — ROAR on how to train and eat with the hormonal tides while you still have a cycle, Next Level on how to replace lost protection with strong external stimuli once hormones withdraw. And the prescription both books write reduces to one script: eat enough (don't fall into low energy), lift heavy enough (real loads), stay fast enough (keep high intensity rather than soaking in moderate cardio), get enough protein (and consider adding creatine), and work with — not against — the physiology you have right now. What holds it up? Partly solid sex-difference physiology and her own hydration/thermoregulation research; partly the early organizing of an emerging, still-incomplete female sports science into actionable advice. And because that second part is "early," the books' value and risk are two sides of one coin: the value is that they put "how women should train" systematically on the table for the first time, giving countless women a starting point that isn't a copied male template; the risk is that some prescriptions run ahead of the evidence and require the reader's own reserve. Even so, the big correction they make — don't hold a woman's body to a man's standard — is important on its own.
① Sims's whole body of work in one line: "women are not small men" — sports science was done almost entirely on men, and copying it onto women is often wrong.
② The two books are two halves of one throughline: ROAR for the reproductive years with a cycle, Next Level for perimenopause and beyond; the dividing line is whether estrogen's natural protection is still there.
③ Mechanistically, estrogen makes women lean on fat and spare carbs, progesterone raises temperature and speeds protein breakdown — so women doing high intensity need to top up carbs and protein and overheat more easily.
④ ROAR splits the cycle in two: the low-hormone follicular phase handles high intensity and PRs well; the high-hormone luteal phase overheats and struggles for intensity, so pre-cool, add carbs and protein, and take magnesium/zinc/omega-3 before the period.
⑤ But honestly: cycle-precise programming is weakly evidenced — reviews find hormone fluctuations likely have small, highly individual effects on performance and resistance adaptation. Adjust by feel; don't obey a rigid 28-day template.
⑥ Her most counter-mainstream and important point: don't train fasted, don't live in low energy; women are more sensitive to energy deficit, which disrupts cycles, harms bone, and wrecks metabolism (RED-S). Eat before a morning workout.
⑦ Women need carbs for high intensity — sugar is fuel, not the villain; for active and especially perimenopausal women, chronic keto often backfires.
⑧ After menopause the rules change: muscle and bone bleed faster, visceral fat accumulates, recovery slows; the old "lots of moderate cardio + light weights" fails, and grey-zone cardio raises cortisol so the more you jog the more belly you store.
⑨ The postmenopausal prescription is to polarize training: heavy strength + true HIIT/sprints + plyometrics — to protect muscle, metabolism, and bone/power respectively; train with more nerve, not gentler.
⑩ Eat harder: get enough protein and a serving soon after training, and consider ~3–5 g of creatine a day (evidence for women's muscle/bone/brain); HRT is a reasonable option for some, but get training, nutrition, and sleep right first.