( ( ( The amount ) ( of ( energy ( in food ) ) ) ) ( ( is ( measured ( in calories ) ) ) . ) )
(ROOT (S (NP (NP (DT The) (NN amount)) (PP (IN of) (NP (NP (NN energy)) (PP (IN in) (NP (NN food)))))) (VP (VBZ is) (VP (VBN measured) (PP (IN in) (NP (NNS calories))))) (. .)))
The amount of energy in food is measured in calories.
(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.