In case the food includes meat of animals slaughtered by mentioning the name of Jesus or any saint over it, it becomes prohibited. Otherwise, food is permissible and there is no problem of eating it as long as it does not lead you to engage in services at the church or in any act of worship. The Prophet (peace be upon him) ate the food of Jews. Moreover, the general rule of the Quran is “the food of those who were given the Scripture is lawful for you and your food is lawful for them.” (An-Nisaa 4:5)