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A Variable Normal

Leah Libresco Sargeant

Dr. Sarah Hill is not afraid of controversy. In her first book, This is Your Brain on Birth Control, she dismantled the idea that birth control makes a woman sterile without changing anything else about her. Hill doesn’t oppose birth control tout court. She rejects the assumption that the standards of informed consent are being met when women aren’t given a full picture of how our hormones (and the Pill’s alternate pattern of hormones) affects our thinking and way of being.

Her newest book, The Period Brain, may be less politically controversial, but Hill is well aware of the dangers of speaking frankly about asymmetries between the sexes. She acknowledges her readers may be uncomfortable talking about the hormonal cycle outside the context of periods and pregnancy. She writes:

As a woman, I understand fearing that if we speak too loudly about the depth of impact our hormones can have on how we think, feel, and act, this could be used to argue that women are inferior to men and therefore undeserving of equal rights.

A world that premises women’s equality with men on our interchangeability with men will necessarily see open talk about biological sex differentiation as threatening women’s political equality. After all, much less stark sex differences in men and women’s conversation styles and conflict resolution strategies have been cited as a reason women cannot be trusted to practice law. Hormonal fluctuations are a much stronger differentiator between men and women, and many women have heard them cited as a put down. However, trying to quash discussion of differences between the sexes is very likely to systematically disadvantage women. When we build public policy or social expectations around either a male norm or a “gender neutral” one, women get shortchanged.

As Hill notes, women’s menstrual cycles have persistently been cited as a reason to exclude naturally cycling women from scientific trials. Including naturally cycling women means scientists have to scale up their sample sizes and track information about cycle phases, so they can normalize their data to account for drug-hormone interactions. It’s simpler to exclude women—or to include only women on the Pill, or only women who are currently in the first, lower-hormone phase of their cycle. Simpler for the scientists, anyway. For women, this results in taking drugs that haven’t been tested to see how they might interact with a normal hormonal cycle, which may cause the drug to be metabolized differently in different phases. For this reason, and many others, Hill thinks the risks of hiding sex differences outweigh the risks of acknowledging them.

Without clear explanations of how our bodies actually work, women struggle to understand or advocate for ourselves. Many women come to see the ordinary variation in the female body and cycle as pathological. I know this first-hand. It wasn’t until I read Taking Charge of Your Fertility in preparation for marriage that I learned one experience in my cycle that worried me was completely normal and a sign of a well-functioning body.

Hill draws a helpful distinction between bodily variations as symptoms or experiences. “Symptoms” are the result of something going wrong within our body; they help us when they draw our attention to a pathology in time to correct it. “Experiences” are noticeable changes in the body that draw our attention, but don’t point to an underlying problem. Becoming sleepy at night is not a symptom in this typology, even though it prompts us to respond. It is simply an experience, a natural part of being a human person, who requires rest at regular intervals.

An entity who was suddenly thrust into a human body and had never had sleepiness explained might treat this experience as a symptom, trying to correct what seemed like a wrongness in their body by drinking more caffeine or turning on more lights, when, in fact, they desperately needed sleep. Some college students do indeed try this approach, despite more than eighteen years of embodiment under their belt. But when we use our bodies against the grain of their functioning, we suffer twice over: first, because we are subverting the natural needs and functioning of our bodies, and second, because we interpret the ordinary functioning of a human body as a personal failure.

Because women’s bodies and hormonal cycles are understudied and underdiscussed, Hill thinks women are poorly prepared to distinguish between symptom and experience. As she puts it:

Many of the things that go on in the luteal phase are experiences masquerading as symptoms. And because we’re not taught what they are, what they mean, and what our bodies need in light of our changing hormonal states, they feel pathological. Like a sign of something wrong.

A middle school health education that only differentiates a woman’s cycle into “bleeding” and “not bleeding” phases leaves girls in ignorance of the natural, hormonal variation they can expect to experience. Because of the surge of progesterone in the luteal phase, for example, it’s normal for women to be more tired and physically weaker during this time. Women who aren’t aware of the way their hormones shape their experience may make plans their body can’t sustain, and then blame themselves for their failure. The absence of clear instruction about hormonal variation makes it harder for women to distinguish non-worrying experiences from the symptoms of PMS or other hormonal pathologies.

Hill’s book gives women a map to understand the ways their physical strength, emotional resilience, and appetites may change in tandem with their hormonal peaks and lows. In many ways, her work represents the best of the MAHA orientation to health. She is focused on the range of individual experience, rather than taking narrow averages as normative for all. She is interested in how women can best respond to the seasons of their cycle, rather than having static, mismatched expectations. She encourages women to chart and experiment, and to get curious about how lifestyle changes and supplements might help them better respond to their personal ups and down.

Hill excels much of the MAHA movement in clearly differentiating which of her recommendations are backed up by gold-standard studies, and where she’s offering more speculative advice, and the evidence base is weak. I’m pretty skeptical of the idea women should “seed cycle” by eating different seeds for different micronutrients in distinct phases of their cycles, for example. Hill is curious about it, but transparent with the reader that this trend has almost nothing supporting it. Still, she’s happy to see a world in which women are actively experimenting with what supports them throughout their cycles. Just keep collecting data and be prepared to reevaluate, she urges.

She closes her book with two injunctions in bold: “Biological sex matters and the existence of sex differences should be assumed until proven otherwise” and “Sex hormones and cycle phase matter and need to be studied rather than statistically controlled for.” Her guidance for scientists is also a much-needed rebuke to the idea that “woman” is primarily a state of mind, not a question of embodiment.

To be just to women, we need to tell the full truth about women’s bodies. Women’s “normal” is more variable than men’s “normal.” Accommodating men and women fully and equally means rejecting a narrow, unsexed norm for either.

Leah Libresco Sargeant is a writer who advocates for a culture that sees the dignity in mutual dependence, instead of aspiring to an impossible autonomy. She runs the Other Feminisms substack, which focuses on the way the world treats women as defective men. Her most recent book, The Dignity of Dependence: A Feminist Manifesto, was published in fall 2025 by Notre Dame University Press.