Stacy Sims’ books are often mentioned together, but they do not address the same physiological situation. If you want to know which book makes more sense for you, the key question is not how “advanced” your biohacking is, but which hormonal phase you are training in and which problems you want to solve.
It is also important to note: many core ideas in both books are plausible and partly consistent with sports and nutrition research. But not every specific rule or timing protocol is directly backed by large, long-term randomized studies. That distinction is crucial for a realistic assessment.
What “Roar” and “Next Level” are each about
In short: “Roar” is primarily aimed at menstruating athletes, while “Next Level” is for women in perimenopause and menopause. Both books aim to adapt training and nutrition to female physiology, but the central difference is the hormonal starting point — i.e. cyclical fluctuations versus persistently altered hormone levels.
At its core, “Roar” is a book about training, nutrition, and recovery under the conditions of an active menstrual cycle. The logic is: women are not simply “smaller men,” and training or nutrition strategies developed almost exclusively in male participants can only be transferred to a limited extent. That basic critique is justified, because women have historically been underrepresented in sports science and many datasets are in fact predominantly male (in several reviews and position papers).
Accordingly, “Roar” focuses on topics such as cycle phases, possible differences in perceived exertion, heat tolerance, recovery, substrate use, and energy availability. Some of this is physiologically plausible and supported by smaller intervention studies, observational data, and reviews. But the evidence base is heterogeneous: for some cycle-related effects, reviews find only small to moderate differences, while for others there are no consistent effects because study designs, cycle determination, and training status vary widely (systematic reviews from recent years).
“Next Level” shifts the focus substantially. Here the topic is no longer primarily a functioning cycle with recurring hormone peaks and troughs, but perimenopause and menopause: a phase in which estrogen and progesterone patterns become more irregular and later drop significantly. That changes the typical problems. Instead of cycle-based periodization, the emphasis is more on loss of strength, changes in body composition, sleep problems, hot flashes, recovery problems, and how to train in midlife.
So both books pursue the same overarching approach: take female physiology seriously. But in practice, each book answers a different question. “Roar” asks: how do I train and eat sensibly within a menstrual cycle? “Next Level” asks: how do I adjust training and nutrition when the hormonal baseline has fundamentally changed in perimenopause or menopause?
Roar vs. Next Level in direct comparison: target group, topics, evidence, and practical value
In short: If you compare both books directly, the picture is clear: “Roar” is more of a cycle book for menstruating athletes, while “Next Level” is a practical book for midlife and beyond. The biggest difference is less about “more methods” and more about target group, typical complaints, training focus, and the type of recommendations derived.
The following comparison is the quickest way to orient yourself:
| Aspect | “Roar” | “Next Level” |
|---|---|---|
| Primary target group | Menstruating athletes, often with a performance or competition focus | Women in perimenopause and menopause |
| Physiological core idea | Cycle-related hormonal fluctuations affect training, nutrition, and recovery | Permanently altered or unstable hormone levels change load tolerance, body composition, and recovery |
| Typical topics | Cycle phases, energy availability, sport-specific adaptations, timing | Strength training, protein, symptom management, sleep, body composition, performance decline in midlife |
| Practical value | Helpful if you menstruate regularly and want to structure training consciously around the cycle | Helpful if irregular cycles, hot flashes, sleep problems, or declining resilience are dominant |
| Evidence base | Mixed: some areas are plausible based on smaller studies and reviews, but many specific cycle rules are not strongly backed by large RCTs | Relatively more robust for basic principles such as strength training, protein, and movement; many specific book rules still not directly tested in RCTs |
| Risk of misuse | Over-fixation on cycle phases can obscure individual differences | Not everything that helps in midlife is automatically useful for younger menstruating athletes |
Methodologically, the most important point is: the strongest evidence usually lies not in book-specific details, but in the basic principles. For strength training in peri- and postmenopause, several intervention studies and meta-analyses show improvements in muscle strength, functional performance, and in some cases body composition (meta-analyses and systematic reviews). For adequate protein intake and the preservation of lean mass in older adults and trained individuals, the evidence is also much stronger than for very specific timing rules (meta-analyses).
By contrast, the evidence for cycle-dependent training recommendations is much less consistent. Several systematic reviews note that while there may be hints of phase-dependent differences, the data are constrained by small samples, imprecise cycle classification, and individual variability. That does not mean the idea is worthless. It only means: the certainty with which some rules are communicated is often greater than the strength of the data behind them.
Which book makes sense for whom
In short: “Roar” is usually the better choice if you still menstruate regularly and want to adapt your training more closely to the cycle. “Next Level” is generally more useful if perimenopause or menopause issues such as irregular cycles, sleep problems, hot flashes, or performance loss are the main concern.
If you menstruate regularly, are physically active, and wonder whether cycle-related differences in training, nutrition, or recovery are relevant to you, “Roar” is probably closer to your lived reality. This is especially true if you do endurance or competitive sports, manage training systematically, or feel that your subjective performance changes across the month. Pregnancy and earlier cycle-related sports questions are also more closely related to this book than to “Next Level”.
“Next Level” is the better fit if your main problem is no longer a “normal” cycle, but cycle chaos or the absence of a cycle in midlife, accompanied by sleep disturbance, hot flashes, slower recovery, altered fat distribution, or loss of strength. This is where the training question becomes very practical: how do you train so that muscle mass, bone health, and performance are preserved as well as possible? For these topics, the evidence base for exercise and strength training is comparatively solid (meta-analyses, guidelines, several RCTs).
The assignment is less clear in cases of hormonal contraception, hysterectomy, endometrial ablation, or other situations in which the cycle is an unreliable marker. Under combined hormonal contraception, endogenous fluctuations differ from the natural cycle; after hysterectomy, bleeding may no longer be available as a reference, even if ovarian activity is partly preserved. Here, especially, book logic does not replace individual medical assessment.
In practical terms, you can ask yourself three questions:
- Do I still have a regular cycle?
- Are my main issues cycle-based performance management or rather midlife symptoms and loss of strength?
- Do I need periodization, or rather a new baseline strategy for a changed hormonal state?
If you can answer these questions clearly, the choice of book often becomes almost self-evident.
Lifestyle levers first: what matters more than any book
In short: Before any cycle- or menopause-specific fine-tuning, the big levers matter most: enough energy, enough protein, regular strength training, sleep, and daylight. For these factors, the evidence is much more robust than for many detailed book protocols or individual supplements.
The most important point is often surprisingly unspectacular: energy availability. Too little energy intake can impair cycle function, recovery, thyroid axis function, bone health, and performance in physically active women. These relationships are well described in sports medicine, including in the context of Low Energy Availability and Relative Energy Deficiency in Sport (RED-S) (consensus statements, reviews, observational data, and intervention data). Not every woman with fatigue, performance decline, or cycle problems needs a complex hormone protocol; sometimes the basic cause is simply too little energy for the training load.
Right after that comes strength training. Especially in perimenopause and postmenopause, it is a central lever because it can positively affect muscle strength, functional capacity, and often body composition (several RCTs, meta-analyses). That makes it more practically important than the question of which supplement is “hormone-friendly.” Similarly relevant is adequate protein intake, especially with higher training volume, calorie deficit, or increasing age. The exact optimal amount depends on context, but it is well established that a higher-protein diet, compared with too little protein, can support the preservation of lean mass (meta-analyses).
Sleep, light, and alcohol are also often underestimated. Sleep problems in perimenopause and menopause are common, but not every complaint of fatigue needs melatonin, magnesium, or exotic blends right away. Regular sleep times, morning daylight, and less alcohol in the evening are often more plausible and more practical first steps. Alcohol in particular can worsen sleep quality, even if it makes falling asleep feel easier subjectively (controlled sleep studies, reviews).
If you want to go deeper into exercise-adjacent fundamentals, a sober look at general health strategies can also help, for example in Peter Attia’s “Outlive”: the key takeaways for longevity. And if your context is more performance-oriented supplementation, Creatine for women: what studies show and which myths are wrong is much closer to a robust evidence base than many hormonal quick fixes.
How strong are the recommendations? Evidence hierarchy and limitations
In short: The basic principles behind both books are often plausible and partly well supported, but many concrete rules are based on smaller studies, indirect inferences, or observational data. Anyone using the books should therefore distinguish between well-supported basics and more hypothesis-driven fine recommendations.
A typical problem in research on female physiology in sport is the small sample size. Many studies on cycle phases, substrate use, training adaptation, or nutrition timing work with relatively few participants. In addition, cycle phases are not always hormonally verified precisely; in some cases they are classified only by calendar data or self-report. This increases the risk of misclassification and weakens the strength of the findings. Accordingly, systematic reviews often conclude that while hints of cycle-dependent differences exist, the data are inconsistent.
The same applies in menopause: not every plausible recommendation has been tested directly as an intervention protocol. That strength training is useful in this life stage is well supported. That adequate protein intake helps preserve muscle mass is also well supported. It becomes more difficult with very specific claims about exact timing, certain nutrient combinations, or universal rules for all women in perimenopause. Here the evidence is often indirect: known physiological changes are combined with general training and nutrition data rather than testing the full book protocol directly.
For practice, a simple evidence hierarchy helps:
- Most robust: large RCTs, meta-analyses, systematic reviews, guidelines
- Moderate: smaller intervention studies, controlled crossover studies
- Weaker: observational studies
- Very limited for direct practical inference: animal models, cell culture, theoretical extrapolation
So when a book gives very clear rules, the key question is: Has this rule been tested directly in humans and in my target group — or is it merely plausible? For nutrition topics, it is also worth being skeptical of overly strict prohibitions. For example, intermittent fasting is sometimes recommended or rejected very broadly, although the evidence is more nuanced and strongly context-dependent; an overview can be found in Intermittent Fasting: what the RCTs show — beyond weight.
Core differences in method, language, and practice
In short: “Roar” works more with cycle phases and sports periodization, while “Next Level” works more with symptoms, loss of strength, and adaptation to a new hormonal baseline. Both books are written for practice, but they organize problems and solutions differently.
Methodologically, “Roar” is more of a book for readers who want to structure, observe, and fine-tune their training. The mindset is phase-oriented: when in the cycle do you feel more capable, and when are you more sensitive to high intensity, heat, or insufficient energy intake? This is attractive for ambitious athletes because it provides a framework for self-observation. But the value depends heavily on how regular your cycle is and how precisely you can recognize patterns at all. In practice, many women respond much more individually than rigid phase models suggest.
“Next Level” often uses more immediate language: it is about typical midlife problems — sleep disruption, abdominal fat, fatigue, declining performance, and the feeling that old strategies no longer work. This perspective is more day-to-day and probably more accessible for many readers than sports-science periodization. At the same time, the focus shifts more toward preserving muscle mass, function, and resilience, which fits the existing evidence well.
Practically, this also means: “Roar” can be inspiring if you see yourself as an athlete and want to work on the levers in the training process. “Next Level” is usually more helpful if you mainly need to accept and shape a new training reality in a sensible way. Like many popular health books, both tend to provide a sense of actionability. That is useful — as long as you treat the recommendations as a working model, not as a law of nature.
One thing remains important: supplements are at most secondary in both contexts. Individual substances can be useful in specific situations, but they do not replace sleep, sensible training planning, or adequate energy and protein intake. The same applies to popular “healthspan” tools such as Vitamin K2 (MK-7): dosage, D3 synergy, and the evidence or immune-related substances such as Quercetin: effects on allergies, mast cells, and the immune system: interesting in their context, but not the first answer to cycle- or menopause-related training problems.
What to realistically expect — and what not to
In short: From both books you should expect not a miracle effect, but rather more structure, better self-observation, and more appropriate basic decisions. They can help you avoid typical mistakes — but they are not a substitute for diagnosis, individual response, or medical assessment.
Realistically, the right book can help you stop aligning your training with an inappropriate standard model. That may mean taking warning signs such as loss of cycle, persistent fatigue, poor recovery, or declining strength more seriously at an earlier stage. That perspective shift is valuable. Many women do not benefit from more complexity, but from a better explanation of why a “more is better” approach fails — for example, when training load, calorie intake, and recovery do not match.
It is not realistic to derive a guarantee of better performance, weight loss, or symptom relief from a book. Individual responses to training and nutrition vary considerably. Training age, genetics, psychosocial stress, sleep, iron status, thyroid function, medication use, and underlying health conditions all play a role. That is why the same strategy can work very well in one woman and make little difference in another.
The boundary to medicine is also important. Heavy or new bleeding disturbances, very irregular cycles, unexplained weight loss, marked exhaustion, persistent insomnia, or major performance drops should be medically evaluated. Books can raise awareness, but they cannot replace diagnostics. That is especially true because symptoms like fatigue or sleep problems are non-specific and can have many causes.
The most sensible way to use both books is therefore as a framework: for classifying, testing, and adapting. Not as a rigid protocol that you follow regardless of your daily life, symptoms, and measurements.
What you should take away
- “Roar” is primarily for menstruating athletes; “Next Level” is usually more useful for perimenopause and menopause.
- The main difference is not “more biohacking”, but the hormonal baseline and therefore the training and nutrition focus.
- More robust than many detailed rules are the basics: enough energy, enough protein, strength training, sleep, daylight, and reducing alcohol.
- The evidence for many specific book claims is mixed: some basic ideas are well supported, but many fine recommendations are only limitedly tested directly.
- Use the books best as orientation, not dogma — and seek medical assessment if symptoms are pronounced or new.