A Syrian family gather to eat a plate of corn and cabbage on November 6, 2017 in Saqba, Syria.

A surge in food prices could cause a massive humanitarian crisis as more than half the world's population is vulnerable to such a risk, Nomura wrote in a recent note.

"The countries most vulnerable to a surge in food prices account for a small portion of the world economy, but make up a much larger share of the world population," Nomura's analysts wrote. "A sustained surge in food prices is unlikely to cause a global economic recession, but it could cause a humanitarian crisis on a global scale."

By its count, the bank said the 50 most vulnerable countries in its index make up just 26.1% of global GDP, but 59.1% of the world. Of those countries, all but four are developing economies, Nomura noted in a recent report.

"The vulnerability to a food price surge is very much an EM phenomenon," Nomura noted.

Concentrated in Africa, the Middle East, and Asia, Nomura said these countries tend to have lower nominal GDP per capita, a high share of food in household consumption, and are large net food importers. The bank said several of the economies most exposed are already "war-torn and suffer from extreme poverty."

According to the Nomura Food Vulnerability Index, the five countries most vulnerable to a sustained rise in food prices are: