( Calories ( ( are ( a ( way ( to ( measure ( food energy ) ) ) ) ) ) . ) )
(ROOT (S (NP (NNS Calories)) (VP (VBP are) (NP (DT a) (NN way) (S (VP (TO to) (VP (VB measure) (NP (NN food) (NN energy))))))) (. .)))
Calories are a way to measure food energy.
(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.