Phrasal verbs are a big problem for non-native speakers – and this week’s mistake is a classic error.
If we gain weight, we often use the phrasal verb ‘put on’ weight, e.g. I put on weight over Christmas. But when we lose weight, you cannot say ‘put down’ weight. It doesn’t work and we don’t use it.
To ‘put down’ means to kill an animal who is in pain, in a situation where it is better to kill them rather than them continuing to live in discomfort. So if you say, „I need to put down some weight“, a teacher might imagine you holding a gun to your belly and shooting off the fat! Well, I would anyway!
Much simpler is to avoid phrasal verbs altogether and just stick to ‘lose’ weight and ‘gain’ weight.