I remember the first time a doctor calculated my body mass index. I was 13 and up until that point had been one of the skinniest kids in my class. But then puberty struck, my hormones went haywire, and I packed on 20 pounds in just a few months. My BMI put me squarely in the "overweight" category. The doctor handed me a food journal and said not to worry—as long as I kept track of every single thing I put into my mouth I could drop those 20 pounds in no time.

Well, I didn't. As I got older, my BMI just got higher. Now, at 25, I'm what the BMI scale considers "obese." I eat a mostly healthy diet, walk everywhere, and do yoga as often as I can. I know people much skinnier than me—people with "normal" BMIs—who literally cringe at the sight of a vegetable. Yet, most doctors would tell them they were perfectly healthy and put me on a strict diet.

What gives?

"We so strongly believe that being fat is bad," says Linda Bacon, PhD, author of Health At Every Size: The Surprising Truth About Your Weight. "It's taught in schools and floods the media." And that's not surprising. Study after study finds that being heavy is associated with illnesses like diabetes, heart disease, and Alzheimer's. But the key word, Bacon says, is "associated."

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According to Bacon, we don't know for sure that being overweight causes the health problems it's been associated with. It could be a combination of many things. For example, people who have high BMIs also tend to have a history of dieting, Bacon says. And research has shown that yo-yo dieting, or fluctuating in weight, has a negative impact on your overall health. "So does illness come from having a higher BMI or from inflammation in the blood due to dieting?" Bacon says. "We just don't know."

There's no denying that the pervasive "fat is bad" lens has led us to believe loads of things about BMI that just aren't true. Here, 5 "facts" you should start rethinking. (Slammed? Even you can squeeze in these feel-good, 10-minute reader-tested workouts!)

Myth: A low BMI ensures that you'll be healthy

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Being heavy has been associated with things like high blood pressure, high blood sugar, and high cholesterol. So it stands to reason that having a low BMI would put all of those things on track, right? Wrong. In a review of several studies looking at BMI, researchers found one study of 40,000 adults that indicated no correlation between high BMI and health issues like high blood pressure and high blood sugar. Plenty of people in the "obese" category had perfectly normal numbers, and plenty who have "normal" BMIs had high blood pressure, blood sugar, and cholesterol.

Bacon, who was an author on the study, says it shows how weight stigma affects health. "Over half of the people on the study would have been misdiagnosed," she says. Because doctors would see people of normal body weight and likely not check for high cholesterol or blood sugar, those people wouldn't get the treatments they need.

Myth: Having a high BMI increases your risk of heart attack

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Like with blood sugar, blood pressure, and cholesterol, many studies have shown an association between high BMI and heart disease risk. Yet a recent self-reported study of 4,046 pairs of identical twins finds that having a high BMI does not increase these risks. In the 12 years that researchers followed the twins, there were 203 heart attacks and 550 deaths among the twins with higher BMIs, and 209 heart attacks and 633 deaths among thinner twins. Even those twins with a BMI of 30 or higher (which would deem them obese), had no increase in heart attack risk.

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Myth: Eating healthy and exercising will always lower your BMI

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Muscle weighs more than fat. So someone who adds exercise and healthy eating to their routine might actually gain weight—and that's not a bad thing. "People can be healthy at different body sizes," says Rebecca Puhl, PhD, deputy director of the Rudd Center for Food Policy & Obesity. Yet, she says, many doctors still stigmatize and place blame on patients they see as overweight, even if those patients are engaging in healthy eating and exercise behaviors.

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Myth: You're healthy if your BMI is between 19 and 25

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In case you don't know, this is how the BMI scale breaks down: A BMI lower than 18.5 is underweight, between 18.5 and 24.9 is normal, 25 to 29.9 is overweight, and 30 or above is obese. But it wasn't always that way.

The National Institutes of Health changed BMI guidelines in 1998, dropping the overweight category from 27.8 to 25. Overnight, a woman who was 5 feet 4 inches tall and 155 pounds was suddenly considered overweight.

At the time, Bacon was a PhD student working on a dissertation on body weight and health. Her advisor was on the committee that made the recommendation, so she asked her why would they recommend lowering the numbers when all evidence pointed toward the need to raise them.

"She said to me, 'Linda, we came to the same conclusion [that the numbers should be raised], but government officials told us that we needed to make a recommendation that aligned with global standards.'" Bacon was floored—how could it be that politics played such a large role in this decision? So she took a look at how the global standards were set. It turns out that the task force that made that recommendation was funded by the only two pharmaceutical companies that made weight loss drugs at that time.

"Those companies stood to gain a lot financially if people who were perfectly healthy one day were overweight the next and would then be prescribed weight loss medication," she says. "It was shocking to realize that a recommendation like that was based more on financial gain than what was best for public health."

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Myth: BMI is a good measure of health

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This one should be pretty obvious by now. Since the guidelines were set without much basis on health and we know BMI doesn't work for everyone, it's pretty clear that it's not an accurate measure of health. Some experts, like Puhl and Bacon, believe that we shouldn't be looking at weight as a measure of health at all.

RELATED: 14 Scales That Do A Lot More Than Measure Your Weight

"When doctors only focus on the number on the scale, this can lead them to oversimplify health issues, ignore other pieces of information, and even stigmatize and blame patients." Puhl says.

Bacon agrees. Focusing on BMI and weight keeps doctors and other experts from seeing the real issues behind disease, she says. It goes back to the difference between "association" and "cause." Research hasn't proven weight to be the cause of most of the things we say it causes, Bacon says. So how can we possibly know that losing weight, or lowering your BMI, is an effective solution? Instead, focus on cooking balanced, satisfying and diverse food— like the recipes from our favorite irreverant cooks at Thug Kitchen.

This article was originally published in Prevention.

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