( Calories ( ( ( ( ( are ( ( a measure ) ( of energy ) ) ) , ) and ) ( used ( to ( measure ( ( how much ) ( ( energy foods ) have ) ) ) ) ) ) . ) )
(ROOT (S (NP (NNS Calories)) (VP (VP (VBP are) (NP (NP (DT a) (NN measure)) (PP (IN of) (NP (NN energy))))) (, ,) (CC and) (VP (VBD used) (S (VP (TO to) (VP (VB measure) (SBAR (WHADJP (WRB how) (JJ much)) (S (NP (NN energy) (NNS foods)) (VP (VBP have))))))))) (. .)))
Calories are a measure of energy, and used to measure how much energy foods have.
(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.