Eugene Diamond spent Tuesday morning dipping strawberries into chocolate at his family’s sweet shop in a small town outside Kansas City. It was the day before Valentine’s Day, and all things chocolate were in high demand.

For Mr. Diamond, a practicing Catholic, another deadline was also looming: This year, Valentine’s Day happens to fall on Ash Wednesday, customarily devoted to penitence and fasting. Starting that day, Mr. Diamond, his wife and eight children will be giving up sweets until Easter, which falls this year on March 31.

Mr. Diamond, 39, taste-tested the sweets at the shop on Tuesday to prepare. “I’ve got to try these today because I’m not going to have a chance to try them tomorrow,” he said.

Ash Wednesday is the first day of Lent, a season marked by sacrifice and solemnity. At church services across the country, clergy members will smudge crosses on parishioners’ foreheads, murmuring, “Remember you are dust, and to dust you shall return.”

The day is meant to serve as a reminder of human mortality, the start of a season that contrasts with and culminates in the joyful celebration of Easter. Practicing Catholics forgo meat on Ash Wednesday, and the church also asks people aged 18 to 59 to eat just one full meal, plus two smaller ones “that together are not equal to a full meal.”

That makes it a tough match with Valentine’s Day, a celebration of romantic love often marked with rich foods, wine and candy.