Weights initially kept Lois fresh (5)
'weights' is the definition.
(I have seen 'Metric weights ' mean 'kilos' so perhaps 'weights' could also mean 'kilos')
'initially kept lois fresh' is the wordplay.
'initially' indicates taking the first letters.
'fresh' indicates an anagram.
The initial letter of 'kept' is 'k'.
'lois' is an anagram of 'ilos'.
(Other definitions for kilos that I've seen before include "Units of mass", "Units of weight in metric system", "Metric weights", "Units of weight of 1000 grams".)