( Calories ( ( measure ( ( the amount ) ( of ( energy ( stored ( in ( a food ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (NNS Calories)) (VP (VB measure) (NP (NP (DT the) (NN amount)) (PP (IN of) (NP (NP (NN energy)) (VP (VBN stored) (PP (IN in) (NP (DT a) (NN food)))))))) (. .)))
Calories measure the amount of energy stored in a food.
(ROOT (S (NP (DT A) (NN calorie)) (VP (VBZ is) (VP (VBN used) (S (VP (TO to) (VP (VB express) (NP (NP (DT the) (NN amount)) (PP (IN of) (NP (NN energy)))) (PP (IN in) (NP (NN food)))))))) (. .)))
A calorie is used to express the amount of energy in food.