Full of calories, it can make you spry around mid-January (5)
I believe the answer is:
syrup
'full of calories it' is the definition.
I can't judge whether this defines the answer.
'can make you spry around mid-january' is the wordplay.
'can make you' indicates an anagram.
'around' means one lot of letters goes inside another.
'mid' means to look at the middle letters.
The middle of 'january' is 'u'.
'spry' is an anagram of 'syrp'.
'syrp' enclosing 'u' is 'SYRUP'.
Can you help me to learn more?
(Other definitions for syrup that I've seen before include "See 12" , "rug?" , "Sugary substance" , "Thick sugar solution" , "Thick sweet sticky liquid" .)