The reason could be that our sense of what’s normal has expanded along with our waistlines. As a new graphic by Nathan Yau of Flowing data shows, the collective weight of Americans has grown rapidly in past decades.

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The simplest way to determine whether a weight is normal is your body mass index – a measurement of the ratio of a person’s weight to height. Physicians typically consider a person with a BMI of less than 18.5 to be underweight; a BMI of 18.5 to 25 to be normal or healthy; a BMI of 25 to 30 to be overweight; and 30 or above as obese. (You can calculate your own BMI here.)

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BMI isn’t a perfect measure; it doesn’t quantify body fat directly, and it can erroneously suggest that athletes or people with a lot of muscle are overweight. For most of us, however, BMI does give an accurate, easy and inexpensive snapshot of our relative weight – as well as a good overall picture of how America’s waistlines have expanded over time.

Yau’s graphic shows how the BMI of Americans has changed over a 30-year period, from 1984 to 2014, according to CDC data. The vertical axis shows Americans’ BMIs – so the higher the bar, the more overweight people are – while the horizontal axis shows what percentage of the American population have that BMI. You can clearly see how our weights have trended upward over the past three decades.

Yau points out some other interesting details. In the 1980s, nearly half of adult American males were already overweight or obese, but the majority of American women were still healthy weights. As the decades passed, however, American women also put on the pounds. In fact, the average American woman today now weighs almost exactly as much as the average American man did in the 1950s, as Wonkblog’s Chris Ingraham has written.

In 2014, 29 percent of American adults were obese and 35 percent were overweight, according to CDC data.

“Basically, “normal weight” is now abnormal and “overweight” and “obese” is commonplace,” writes Yau.