GUATEMALA CITY — In the tiny tortillerias of this city, people complain ceaselessly about the high price of corn. Just three years ago, one quetzal — about 15 cents — bought eight tortillas; today it buys only four. And eggs have tripled in price because chickens eat corn feed.

Meanwhile, in rural areas, subsistence farmers struggle to find a place to sow their seeds. On a recent morning, José Antonio Alvarado was harvesting his corn crop on the narrow median of Highway 2 as trucks zoomed by.

“We’re farming here because there is no other land, and I have to feed my family,” said Mr. Alvarado, pointing to his sons Alejandro and José, who are 4 and 6 but appear to be much younger, a sign of chronic malnutrition.

Recent laws in the United States and Europe that mandate the increasing use of biofuel in cars have had far-flung ripple effects, economists say, as land once devoted to growing food for humans is now sometimes more profitably used for churning out vehicle fuel.