That is still low compared with the United States, where 36.5 percent of the adult population was clinically obese in 2014, according to the Centers for Disease Control and Prevention. (International standards define being obese as having a body mass index of 30 or higher, and overweight as a B.M.I. of 25 to 29.)

Activists trying to increase public awareness about the problems the obese face, and demanding that the French Health Ministry disseminate more information about treatment options, are only beginning to get a hearing, said Anne-Sophie Joly, president of an umbrella association of groups representing obese people.

“Society is very harsh with women,” Ms. Joly said. “Women face the most demands: She must be beautiful, but not too much; she must be thin, but not too thin; she must be intelligent, but not too much because you mustn’t put the man in the shadows.”

Ms. Deydier, a native of the southern city of Nîmes, studied literature as well as a bit of politics and philosophy in Montpellier and has worked in journalism. In her book, she describes with sometimes caustic candor the daily humiliations of “grossophobie,” or fat-phobia, in France.

France is one of few countries prohibiting job discrimination based on physical appearance, in a 2001 law, but the measure appears to be more often ignored than observed.

Jean-François Amadieu, a sociologist at the Sorbonne in Paris who tracks public perceptions of obesity, said that obese men were three times less likely to be offered job interviews, and obese women six times less likely. (It is customary in France for job applicants to include photographs with their résumés.)

Ms. Deydier recalled applying for a job at McDonald’s as a university student, when she weighed around 200 pounds. The manager “didn’t want customers to see me working there,” she said, “because he didn’t want them to think they would look like me if they came often.”