Juice Fasting in Winter

My co-worker and I are considering doing a 7 day juice fast.
It would be a first fast/cleanse/detox for either of us.
We live in Canada and despite it being a relatively mild winter for us, we have heard advice that any fast or cleanse should not be done in the winter.
What is the general consensus or opinion on this?
We're eager to try the juice fast but don't want be ignorant about doing it in winter if there is a risk or major concern.

Any advice is appreciated.