As heat potential and energy potential are biochemically related, food calories are a measure of the latent or potential energy in the food, and hence provide an estimate of (or proxy for) the energy that you can derive by eating and digesting the food.
(food calories; are; a measure of the latent or potential energy in the food) (the energy; can derive; by eating and digesting the food)
food calories the energy
are can derive
a measure of the latent or potential energy in the food
by eating and digesting the food