Chicago ? Call her The Incredible Shrinking African-American Woman.

In an age when the adult populations of most industrialized nations have grown significantly taller, the average height of black women in the U.S. has been receding, beginning with those born in the late 1960s.

The difference in stature between white women and black women has now stretched to three-quarters of an inch and appears to be increasing, according to newly released data from the National Health and Nutrition Examination Survey conducted by the federal Centers for Disease Control and Prevention.

The main culprit appears to be diet.

The average height of a black woman born in the 1980s is just under 5 feet 4 inches; her mother, born in the 1960s, is more than half an inch taller. Even her grandmother, born in the 1940s, is a bit taller. The average white woman born in the 1980s is about half an inch taller than her mother.

The gap is “truly phenomenal,” according to John Komlos, an economist and historian who has made a specialty of studying human heights. “Such a steep decline is practically unprecedented in modern U.S. history.”

You have to go back to the antebellum South to find a similar shrinkage. The generation of white men born in the 1840s who experienced the ravages of the Civil War lost nearly an inch to their Northern counterparts, Komlos said.

Komlos, who has been studying heights since the early 1980s, says the downward trend among black women was “quite unexpected.”