( Calories ( ( are ( ( the measurement ) ( used ( to ( express ( ( the energy ) ( delivered ( by food ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (NNS Calories)) (VP (VBP are) (NP (NP (DT the) (NN measurement)) (VP (VBN used) (S (VP (TO to) (VP (VB express) (NP (NP (DT the) (NN energy)) (VP (VBN delivered) (PP (IN by) (NP (NN food))))))))))) (. .)))
Calories are the measurement used to express the energy delivered by food.
(ROOT (S (NP (NP (DT The) (NN energy) (NN content)) (PP (IN of) (NP (NNS foods)))) (VP (VBZ is) (ADVP (RB often)) (VP (VBN expressed) (PP (IN in) (NP (NNS calories))))) (. .)))
The energy content of foods is often expressed in calories.