You cannot actually ‘lose’ weight on purpose, because ‘to lose’ something means that you have done so unintentionally.
I’ll grant you that ‘to lose’ also has an alternate definition which includes intention, as in ‘to lose someone who is chasing you’, but, let’s be practical: that’s not what is conventionally meant when we say ‘to lose weight’.
Perhaps the expression ‘to lose weight’ would yield more results if a bit of intention were added.
So, for example you could say “I intend to lose weight.” Or better, “I intend to lose twenty pounds by March 1st.”
Or, “I am reducing my weight by using this process.”
Try it out.
It’s better to put yourself in control, than to leave it to chance.