For more than two decades, economists have noticed that obesity has a, well, weighty impact on income, particularly for women. A well-known 2004 study, for example, found that a 65-pound increase in a woman’s weight is associated with a 9-percent drop in wages — an obesity penalty equivalent to about three years of work experience.

“But economists have been really puzzled as to why,” says Jennifer Bennett Shinall, an assistant professor of law at Vanderbilt University. “Why are female obese individuals doing worse in the labor market?”

Research has focused on three possible explanations. The first points the finger at the employee herself. It says that obese women are choosing to work in jobs that happen to pay less.

The other two explanations focus