Cook boils meat mass — this gives you energy (10)
I believe the answer is:
metabolism
'this gives you energy' is the definition.
(metabolism gives the body energy)
'cook boils meat mass' is the wordplay.
'cook' is an anagram indicator.
'mass' becomes 'm' (symbol used in Physics e.g. f=ma).
'boils'+'meat'='boilsmeat'
'boilsmeat' with letters rearranged gives 'metabolis'.
'metabolis'+'m'='METABOLISM'
(Other definitions for metabolism that I've seen before include "Vital chemical processes in a living organism - mobile ATMs (anag)" , "it's what keeps him going" .)