Third-wave feminism tells girls that we can be both empowered and feminine. We can be CEOs in heels and lipstick; we can (almost) be president in a skirt and pantyhose; we can (sort of) be sexual aggressors in a mini-dress. We can have it all. We are liberated. But the ideology of “beautiful femininity” is not a choice — it’s a social mandate.

There are few female role models for young women to emulate, beyond the anemic frames of actresses and models. Now in my third year at Yale, I’ve had 20 male professors. My syllabi feature Plato, Descartes and Kant. Walking across campus, I see the gallant figure of Nathan Hale, the venerable iron-cast of Woolsey, the names of fallen men inscribed on Beinecke plaza. I’ve admired the sepia self-assurance of Yale’s sportsmen that line the walls of Mory’s. I’ve scanned the portraits of past masters as I eat breakfast, lunch and dinner.

Most of the women commemorated throughout history are not great minds or inspirational leaders. In fact, they aren’t individuals at all. Their smiles are carved or painted ever so delicately in bronze and stone and oil. They are all beauties, abstracted.

They’re also 25 pounds heavier than any model you’ll see today in Vogue.

According to a UK magazine, the average woman today worries about the size and shape of her body every 15 minutes. Twenty-nine percent said they worry about their body every waking moment. Seven out of 10 women can look at a plate of food and tell you exactly how many calories are in it.

Of my seven best friends at my all-girls private high school — all smart, all attractive, all ambitious — three received medical attention for their self-starvation. During lunch hour, everyone would quietly compare how little of their dressing sachet they each drizzled on their lettuce leaf pile. They would chew some ice cubes. They left the bread.

Roughly 0.5 percent of American college students are anorexic, 2 percent are bulimic and 4 percent binge eat. These are mental illnesses. As many as 80 percent of undergraduates have disordered eating. The statistics are murky, but the fact is not: A large number of the women on our campus are sick.

The phenomenon is what Naomi Wolf attributes to “the beauty myth”: As women advance, physical obsession and self-hatred undermines our progress. The fiction of beauty is the last old feminine ideology with any real traction. Women no longer worship the holy trinity of motherhood, domesticity and chastity. Wolf writes: “the gaunt, youthful model [has] supplanted the happy housewife as the arbiter of successful womanhood.”

Female oppression has always been founded on the eroticization of domination: corsets; foot binding; female genital mutilation; the virgin; the whore; the docile wife; the obedient homemaker. The pressure to be beautiful is based on the same principle. Society now recognizes the injustice of most of these phenomena, but the beauty myth persists. It’s justified as innate: Beauty indicates a woman’s effectiveness as a breeding machine. The desire for beauty, therefore, must be hard-wired.

Beauty, however, is not biological or immutable. It is a transient mass consensus that varies vastly across cultures and time — far more rapidly than evolution. It is political. It is a prescription for the female’s relation to her body, for female behavior and female thought.

Dieting came into vogue around 1920, when women received the vote, reversing centuries of exultation in free-flowing female flesh. Ruben-esque fullness returned to the fore in the socially regressive 1950s, only to be undone as women’s legal and political influence grew. Between 1960 and 1969 the number of high school girls who considered themselves overweight increased from 50 to 80 percent.

Greater equality only came with a hefty side order of self-hatred. By 1984, in a Glamour poll, losing 15 pounds beat out romantic and career success as women’s most desired goal. By 1997, young girls indicated on surveys that they were more afraid of being overweight than of cancer, nuclear war or being orphaned. Girls were less scared of blowing up into chunks than blowing up into chunky.

In the ’60s and ’70s, women’s liberation threatened the patriarchy. Men’s jobs were threatened by a mobilized, female underclass willing to work for a lower wage. Women were newly assertive, empowered and educated. They demanded rights. They ran for office. Male power structures could no longer use old, archaic means to sustain themselves. The consequence: a beauty backlash, designed to temper female advancement and secure male power and maintain the status quo.

It came in the form of direct, but subtle, beauty discrimination. For example, why do most male newscasters have receding hairlines and massive jowls, while most female newscasters are young, hot, blonde and plastered in make-up?

The beauty myth also lowers women’s self-esteem. The gender wage gap, the feminization of poverty, unaffordable child-care, lack of political representation, insecure reproductive rights, unequal domestic burdens — these are the issues that should galvanize women. But every 15 minutes women are distracted by their stomach roll or the chaffing in the hip of their jeans or the extra piece of cake they ate after dinner.

Mentally castrate, women are politically appeasable: quiet, preoccupied and insecure. When oppressed, women are kept from demanding what we are truly worth — the same as men.

Insecure women are also excellent consumers. In women’s magazines, sandwiched between articles about sort-of maybe legitimate women’s concerns, ads for slimming pills and shimmer foundation painted on svelte adolescents fill the pages. If you can never be too skinny or look too much like a sparkly pedophile victim, you will be an insatiable buyer. The weight-loss industry grosses $40 billion a year — straight out of women’s newly minted wallets.

The pervasive and unhealthy preoccupation with weight should engender a sympathetic and defiant community: a network of women who collectively act against the social forces that breed disordered eating. The world would be a Dove commercial. Or the Women’s Center.

Instead, the opposite is true. Women slyly comment, with a creepy hint of jealousy: “She’s lost so much weight”; “She’s so skinny.” We have internalized the beauty myth; we reel at the possibility of another woman, an adversary, increasing her beauty status. Women are not united, but atomized and mutually threatening. Poisoned by our own insecurity. Paralyzed by the fear of being unattractive.

According to the media, women are only beautiful when they are underweight. Female perfection is not achieved through self-fulfillment, but as always, self-denial. This used to be the denial of public influence and sexual desire. Now, it’s dessert. The natural female state, we are told, is too fat; the natural female state is defective.

The beauty myth casts its shadow over the boardroom and the bedroom. Contraception is now readily available, abortion is legal and the sexual double standard has largely eroded. However, sex for women is still too often shameful and pleasureless. Women can have multiple, polymorphic and sustained orgasms, but roughly 30 percent of women have never had an orgasm at all.

Half of all women surveyed in the UK said their body size and shape ruined their sex life; it’s hard to have an orgasm if you’re sucking in your stomach and imagining yourself 10 pounds lighter. Ironically, fat is the medium of female sexual characteristics: the hips, the breasts, the ass and the sex hormones. If a woman’s fat-to-lean ratio falls too low, she delays puberty, loses her libido, destabilizes her menstrual cycle and risks infertility and ovarian cancer.

Pornography, which grosses $10 billion to $14 billion annually, usually employs a male subjective, which constructs an image of sex in which the woman is passive, objectified, perfect, plastic and degraded. This is the version of female sexuality that our society, men and women alike, learn.

Bombarded with these images, women come to be aroused by desirability, not desire. As the critic John Berger said: “Men look at women. Women watch themselves being looked at.” This picture of desirability is unattainable, which makes it difficult for women to accept themselves as attractive and worthy of sexual fulfillment. As women grow more self-assertive and empowered in the public sphere, pornography, film and advertising ensure a private dehumanization.

Our culture teaches women nothing about what they want. It teaches men nothing about what women want either. What do women want? It isn’t inscrutable, but culturally invisible. Hint: It’s not Luna bars.

Women live in a society that will only love us if he hate ourselves; reward our minds if we deny our bodies; give us political, sexual and economic equality if we don’t fulfill its promise. As a result, we remain disempowered, de-sexed and dependent.