You'll be seeing more body types in our workout stories — here's why

Two years ago this month, I proclaimed we'd no longer be using the phrase "bikini body" in Women's Health. Since then, body diversity has dominated the national conversation. Plus-size models walk the runways of Michael Kors and Tracy Reese. Celebs who aren't size 2 grace fashion and wellness magazine covers.

And on Instagram, there are over 4 million #BodyPositive posts. It's been a great thing, inclusivity, as a boon to our emotional health, but also as a realistic statement to society of who we are as American women.

The fitness industry has been slower to adapt. Yes, Misty Copeland rocked the willowy ballet world with her spectacular muscles, and Jessamyn Stanley, a self-described "fat femme," became a yoga icon.

But most mainstream workout videos and printed moves are populated by the stereotypical "fit" woman: slender, toned but not too cut, without a pinch of fat. Because... why? Can you not be a size 8, 12, 16 and be fit? Why has fitness remained the holdout in the body diversity movement?

To answer the question, I first had to completely understand what, in technical terms, makes someone physiologically fit. I called on two experts, who explained the metabolic metrics.

These include: resting heart rate and VO2 max, a measure of aerobic capacity, or how efficiently your body uses oxygen; blood markers, like blood pressure, glucose, insulin, and cholesterol; and body composition, the ratio of fat, bone, water, and muscle in your body.

What's not on the list is just as telling. Weight. "I think the most important thing when considering fitness is to throw out weight or size," says exercise physiologist Linda Bacon, Ph.D., who has conducted journal-published studies on health and weight.

You'll never believe these photos were taken 60 seconds apart:

My other pro, exercise physiologist and nutrition scientist Stacy Sims, Ph.D., puts it this way: "You can be thin yet have the body composition of someone who's obese. And you could be heavier on the scale but have a significant amount of lean mass, so your overall percentage of body fat would be healthy."

In all the noise around obesity, weight and body fat have been conflated. And while high levels of the latter are a risk factor for cardiovascular disease, high blood pressure, diabetes, and certain cancers, both experts say the role of weight itself in health has been exaggerated.

Eating well and being active are what's important, whether you drop pounds or not. (Genetics and gut bacteria—the kind that promote fat storage—can prevent some people from ever being thin, says Sims.)

And many studies linking weight loss to health speak of correlation, not causation, says Bacon, who believes that scientists (and the rest of us) often interpret the data through our internalized fat biases.

Where, then, did these assumptions linking a certain weight with a fit body come from? Toward the end of World War II, Sims explains, the U.S. government had to ration foods, which it did using calorie content per person.

This focus on calories—and a new emphasis on slim models in fashion magazines—continued postwar, leading to a thin ideal. When the obesity epidemic hit in the '80s, people doubled down on the idea that extra pounds = bad health. "So it became 'you have to lose weight,'" says Sims. "But it's not that simple."

To wit, body mass index (BMI), a weight-to-height ratio that for decades was the standard for measuring a person's health, has been debunked.

A 2016 study found that 47 percent of people in the overweight BMI category, and 29 percent classified as obese, were actually healthy.

And 30 percent of those with "healthy" BMIs had too-high blood pressure, cholesterol, inflammation levels, or insulin resistance—all those factors crucial to physical fitness.

More proof there isn't one type of fit body? CrossFit. "You see all shapes and sizes," says Sims. "People who don't look like they can lift or pull heavy weights can do strict pullups and heavy deadlifts. You never know who's going to be the strongest or the fittest." This is an important message not just for heavier folks.

"As long as we keep our message on body size," says Bacon, "people think if they can maintain their thin bodies, fitness doesn't matter." Yet exercise is critical to overall health. (For more news about the body-positivity movement, sign up for Women's Health's daily newsletter, So This Happened.)

WH wants to champion this truth of fitness diversity, so we will no longer be using fitness models in our monthly "15-Minute Workout." We'll feature readers of various body types and sizes. (We'll still have fitness models in the mag—they're women too! And it's logistically difficult to book nonmodels who have day jobs.)

We also have a new DVD with CrossFit coach Hannah Eden, whose ripped muscles are as rare in mainstream DVDs as size 8s. It's all part of our #IAmFit campaign launching this month—small steps we hope can lead to real change in perceptions. Because, as Bacon puts it, "You can't tell anybody's fitness status by looking at their body. The only thing you can judge by looking at somebody's body is your level of prejudice."

Check out @WomensHealthMag on Instagram for inspiring stories of everyday women getting their fit on in everyday ways. And join in by posting your own fit reality, tagging us and using the hashtag #iamfit. Let's change the world together!

This article originally appeared in the January/February 2018 issue of Women's Health. For more great advice, pick up a copy of the issue on newsstands now!