( ( A calorie ) ( ( is ( ( a measure ) ( of ( energy ( provided ( by food ) ) ) ) ) ) . ) )
(ROOT (S (NP (DT A) (NN calorie)) (VP (VBZ is) (NP (NP (DT a) (NN measure)) (PP (IN of) (NP (NP (NN energy)) (VP (VBN provided) (PP (IN by) (NP (NN food)))))))) (. .)))
A calorie is a measure of energy provided 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.