Clue: Food that makes us extremely slim. lithe and invigorated, for starters (6)
Answer: MUESLI
Explanation: Food that makes us extremely slim. lithe and invigorated, for starters (6)
First letters of **M**akes **U**s **E**xtremely **S**lim **L**ithe and **I**nvigorated 
*I don't like the "and" being *in there.