It also showed policies on which everyone’s supporters mostly agree. Supporters of all the candidates give the president a low approval rating, disapprove of the military strike that killed the Iranian general Qasem Soleimani, and believe the president should be removed from office. One policy area where there was less agreement was on whether the United States should withdraw its military forces from the Middle East. Iowans who supported Mr. Sanders were the most in favor of the withdrawal, while those of Amy Klobuchar were the most critical.

There were no discernible differences on most of the nonpolitical questions across the candidates’ supporters in Iowa, such as on buying organic foods (most supporters of all the candidates think it’s important), using Twitter to read political news (most don’t) or watching television shows on premium outlets (also uncommon). Accounting for things like age and education soaked up most of the differences that appeared at first glance.

But, as has also been true in past contests, Indian food was a distinguishing characteristic. In Iowa, supporters of Mr. Sanders are its biggest fans: 71 percent of them report going to an Indian restaurant sometime in the last 10 years. Mr. Biden’s supporters are less likely to have done so by about 30 points. This makes sense. Mr. Sanders’s supporters are younger and perhaps more likely to live in the college towns or in major metropolitan areas. Still, this relationship persists even after accounting for age, race, gender, education, ideology, being an independent, or where a person lives in the state.

Mr. Biden loses 14 points of vote share among those who have been out for Indian food relative to those who have not, and Elizabeth Warren loses three. Mr. Sanders gains eight points, Pete Buttigieg gains five, and Ms. Klobuchar gains four.

Of course, it’s not that eating Indian food leads a person to support one Democratic candidate over another — that’s silly. (And there are voters for whom Indian food is the taste of home.) But a voter’s orientation toward the world is related to candidate choice, and it turns out that eating in restaurants that celebrate less familiar cultures is one way to measure where people think they are more connected: to those around them locally or to people farther afield.

Which Democrats will prevail this primary season — the cosmopolitans or the local-focused? Something to consider the next time you eat out.

Lynn Vavreck, the Marvin Hoffenberg Professor of American Politics and Public Policy at U.C.L.A., is a co-author of “Identity Crisis: The 2016 Presidential Campaign and the Battle for the Meaning of America.” Follow her on Twitter at @vavreck.