Americans have some truly wrong-headed ideas about what healthy bodies look like.

In February, model Ashley Graham became the first plus-size model to land the cover of Sports Illustrated’s annual Swimsuit issue. The backlash against the 5’9, size 14 model was swift. As usual, the objections centered mostly around the “unhealthy” message sent by photos that celebrate women larger than traditional models. Former supermodel and SI cover girl Cheryl Tiegs added her two cents: “Actually I don’t like that we’re talking about full-figured women, because it’s glamorizing them—because your waist should be smaller than 35 [inches]. That’s what Dr. Oz said, and I’m sticking to it. No, I don’t think it’s healthy.”

Tiegs’ invocation of TV show host and controversial health guru Dr. Mehmet Oz as her source of reliable health information should immediately raise red flags. Researchers have found that “nearly 4 in 10 of the assertions made on [his] hit show appear to be made on the basis of no evidence at all.” Due in part to misinformation and outdated research, many Americans, like Tiegs, continue to lump together anyone who doesn’t look traditionally skinny, automatically labeling them unhealthy. (Tiegs also incorrectly assumed Graham’s waist was larger than 35 inches, which it isn’t. She has since (sort of) apologized.)

It’s actually quite difficult to tell whether someone is medically defined as obese simply by looking at them.

The first problem lies in how we categorize an oversight person. Despite what people like Tiegs might think, it’s actually quite difficult to tell whether someone is medically defined as obese simply by looking at them, let alone whether that person is actually unhealthy.

The standard medical model for determining whether a person is carrying around too much fat is by body mass index, or BMI. Created in the 19th century by Belgian mathematician, astronomer and statistician Adolphe Quetelet, BMI has become the fallback standard for evaluating how fat is “too fat.” Grade 1 obesity (low-risk obesity) is classified as a BMI between 30 and 35; Grade 2 and 3 (moderate to high-risk) obesity requires a BMI of over 35.

If you believe that the BMI is a sound way of measuring someone’s overall health, you might be surprised to learn that, according to a 2013 study in the Journal of American Medicine, people with a BMI categorized as “overweight” or “Grade 1 obesity” were actually at a lower risk of mortality than people whose weight fall into the “normal” category. Ashley Graham, in other words, may be statistically likely to live longer than Cheryl Tiegs will.

Ashley Graham, in other words, may be statistically likely to live longer than Cheryl Tiegs will.

Indeed, some researchers argue that BMI is a flawed metric, particularly when it’s used as the main indication of a person’s health. That’s because the BMI neglects to take into account such factors as body fat percentage, whether a person is active or sedentary, and what their individual body measurements are. Tiegs is right, in a limited sense, that waist size might be a good judge of health—but only in proportion to a person’s height.

More importantly, however, researchers’ understanding of the relationship between weight and health has evolved greatly, especially over the past decade. For one thing, scientists continue to investigate a phenomenon known as the obesity paradox, in which people with elevated BMIs seem to be aided in their survival of particular conditions or diseases because of—not in spite of—their weight. This is particularly true in cases of patients with a wide range of conditions including stroke, coronary heart disease, Type 2 diabetes, and osteoporosis. Why this should be the case, and what the paradox means for the medical community, is a matter of much scientific debate.

Stereotypes about beauty standards and body types shouldn’t be used to evaluate a person’s well-being.

None of this is to dismiss research showing the negative health effects of obesity. Carrying around an excess amount of weight—especially in your midsection—can and does put people at higher risk for a variety of conditions and illnesses, and even mortality. But that doesn’t mean stereotypes about beauty standards and body types should be used to evaluate a person’s well-being. When medical doctors can’t even agree on what the definition of obesity should be, the opinions of your average man on the street are essentially useless.

And yet, objecting to representations of “plus-size” figures remains at least somewhat culturally acceptable when it’s done under the guise of health concerns. If a model is depicted in an ad with a bottle of champagne, people don’t flood the internet alleging that she’s promoting alcoholism, or that she’s partly to blame for the 223.5 billion dollars the US Centers for Disease Control estimates that excessive drinking costs the American economy each year. If we’re so concerned about cultural messages of health, we’re awfully selective about it.

We need to stop lying to ourselves. People don’t body shame one another out of altruism–they do it with the intent to embarrass and shame. Deep down, we know it’s not socially acceptable to admit the sight of a person who doesn’t conform to cultural norms of weight or shape makes us uncomfortable. And so we grasp at science to make our “concern” seem legitimate. If women want to look up to Ashley Graham, they should. She just might be healthier than any model ever to grace the cover of Sports Illustrated.