This is not recommended by all fasting practioners, especially, Dr. shelton, Furhman, and many more. This is also very logical, your body is using all it's energy for healing and cleaning and exercise and cool temperratures stop that process, or slow it down. Rest is vital when fasting.
Walking is permitted if you are looking to lose weight, but relaxed walk.
There are other ways to curb hunger pangs is to drink warm or hot water.