I came up and had a meal to bring about weight loss (8)
I believe the answer is:
emaciate
'bring about weight loss' is the definition.
I can't tell whether this definition defines the answer.
'i came up and had a meal' is the wordplay.
'up' is a reversal indicator (in down clue: letters go upwards).
'and' says to put letters next to each other.
'had a meal' becomes 'ate' (ate a meal).
'i'+'came'='icame'
'icame' in reverse letter order is 'emaci'.
'emaci'+'ate'='EMACIATE'
'to' is the link.
Can you help me to learn more?
(Other definitions for emaciate that I've seen before include "Waste away" , "Make extremely thin" , "get very thin" .)