BOSTON — Most Boston Marathon runners will participate in the tried-and-true practice of loading up on carbohydrates before Monday’s race. But some runners will defer to a much holier practice this year and replace their bread and pasta with matzo and potatoes.

The marathon falls on the second day of the Jewish holiday of Passover, when eating leavened bread is forbidden for eight days because of dietary rules.

For many runners used to filling up with carbohydrates in the days before a race, exactly what to eat, and not eat, to perform optimally and still obey the rules of Passover is somewhat vexing.

“We’re carb loading on matzo,” said Rabbi Jonah Pesner, who is running his first marathon.

Pesner and his wife, who are running the race for an autism-research charity, are having a Seder Sunday night with side dishes like potatoes and matzo ball soup, which has the sodium that runners need.