Officials acknowledge that officers will still be able to grab a bite on the beat, easily defeating the department’s dietary guidelines. “We have to accept that the culture of snacking is present in most of the population, and the police also have this habit,” Dr. Peniche said. But the department still hopes to inculcate better eating habits in the police force.

Mexicans as a whole have rapidly expanding waistlines. The Health Department said in a report released this year that obesity levels in Mexico were second in the world only to those in the United States, and the problem is especially acute among the young.

And it is not just large portions that are the problem. Mexicans do not exercise enough, officials say, and a recent government health study found that Mexicans consumed almost twice the amount of salt recommended by the World Health Organization, leading to elevated rates of hypertension, heart disease and kidney failure along with obesity.

Many Mexico City officers are going along with the healthier menus, and initial reports are that waistlines are shrinking. But there is also plenty of cheating as officers admit to supplementing their official fare with more filling food from the street  overflowing tacos, tortas, quesadillas and huaraches, all washed down with sugary sodas.

“It’s good to lose weight,” acknowledged Crescencio Aguilar, 48, an 18-year veteran of the transit police who weighs just over 200 pounds, has a protruding abdomen and was interviewed near a rather aromatic stand selling beef tacos and quesadillas. “But the truth is, the way I am, I’ve been chubby since I was a boy, and it’s going to be difficult to drop down.”