Clue: Cook steak dinner primarily? Win, having lost weight with it? (6,4)
Answer: ATKINS DIET
Explanation: Cook steak dinner primarily? Win, having lost weight with it? (6,4)
An anagram ('cook') of 'steak' plus D ('**D**inner primarily') plus '[w]in' minus the W ('having lost weight') plus 'it', with an &lit definition.