"He is losing weight"
IMHO there is a mismatch between the English and the Swahili sentences.
He is losing weight (because he is ill): Anakonda (kwa sababu anaumwa)
He is slimming: Anajikondesha. The reflexive -ji and the causative -esha make the literally translation 'he is causing himself to lose weight', that is: 'he is slimming'.